Publications

genetic analysis of essential plasmid determinants of pathogenicity in yersinia pestis.	the role of the yersinia pestis virulence-associated plasmid, pyv019, in the expression of ca++ dependence, virulence, and the production of the v antigen was investigated. derivatives of bacteriophage p1 were used to deliver the transposon tn5 into y pestis strain ev76. ca++-independent mutants in which transposon tn5 had been inserted into plasmid pyv019 were isolated, the resulting plasmids--pyv019::tn5--were transformed into an escherichia coli k12 derivative, and the site of insertion of tr ...	1983	6310003
transductional instability of tn5-induced mutations: generalized and specialized transduction of tn5 by bacteriophage p1.	generalized transduction is commonly used to move transposon-induced mutations among bacterial strains by selecting for inheritance of a transposon-encoded resistance determinant. although complete cotransduction of the resistance determinant and the chromosomal mutation might be expected, it is often found that when tn5(kan) insertion mutations are transduced by bacteriophage p1 most of the nonmutant kanamycin-resistant transductants area due to specialized transduction of tn5. such p1::tn5 spe ...	1983	6313472
sequence of the site-specific recombinase gene cin and of its substrates serving in the inversion of the c segment of bacteriophage p1.	inversion of the 4.2-kb c segment flanked by 0.6-kb inverted repeats on the bacteriophage p1 genome is mediated by the p1-encoded site-specific cin recombinase. the cin gene lies adjacent to the c segment and the c inversion cross-over sites cixl and cixr are at the external ends of the inverted repeats. we have sequenced the dna containing the cin gene and these cix sites. the cin structural gene consists of 561 nucleotides and terminates at the inverted repeat end where the cixl site is locate ...	1983	6315399
the sequence of the bacteriophage p1 genome region serving as hot target for is2 insertion.	a restriction fragment of the bacteriophage p1 genome known to serve as a hot target for is2 insertion in its host, escherichia coli k12, was entirely sequenced. it is 1756 bp long and it contains four long open reading frames, all in the same orientation. the two middle frames overlap partially. eight of the nine studied is2 insertions affecting phage reproduction map within three of these reading frames. no common feature was found between the nine target sites which have served for is2 integr ...	1983	6315401
site-specific recombination of yeast 2-micron dna in vitro.	most strains of the yeast saccharomyces cerevisiae harbor several copies of a 2-micron plasmid circle dna termed "2 micron." this circular plasmid contains two 599-base-pair precise inverted repeats across which a site-specific inversion event occurs in vivo. this inversion is promoted by a plasmid-encoded function called "flp." we have cloned the flp gene of 2-micron dna under control of a strong yeast promoter and transformed yeast cells with a plasmid containing the cloned flp gene. cell-free ...	1983	6316354
genetic mapping of the minb locus in escherichia coli k-12.	the minb (minicell production) locus of escherichia coli k-12 was mapped by transduction using bacteriophage p1. minb is located at min 25.6, between purb (min 25.2) and dadr (min 25.8). the mapping was facilitated by the use of insertion zcf-236::tn10, which is inserted at min 25.4.	1983	6296039
recombination-induced suppression of cell division following p1-mediated generalized transduction in klebsiella aerogenes.	klebsiella aerogenes recombinants resulting from bacteriophage p1-mediated generalized transduction failed to increase in number for approximately six generations after transduction. nevertheless these recombinants continued to grow and became sensitive to penicillin after a transient resistance, suggesting that the cells were growing as long, non-dividing filaments. when filamentous cells were isolated from transduced cultures by gradient centrifugation, recombinants were 1000-fold more frequen ...	1983	6343791
salmonella typhimurium lt2 strains which are r- m+ for all three chromosomally located systems of dna restriction and modification.	we describe the derivation of two strains of salmonella typhimurium lt2 which are r- m+ for all three of the known chromosomal genes for the restriction and modification of dna, hsdlt, hsdsa, and hsdsb; the strains were designated lb5000 and lb5010. lb5000 is a smooth derivative sensitive to phage p22; lb5010 is a gale strain sensitive to phage p1.	1983	6352690
electron microscopy study of early lytic replication forms of bacteriophage p1 dna.	p1 replication intermediates were isolated from the intracellular dna of lytically infected cells and analyzed by electron microscopy. at early times in infection replication intermediates were mainly of two types, circular theta- and sigma-shaped molecules plus a small proportion of linear bubble-shaped molecules. at later times in infection sigma molecules were the predominant replicating form. in contrast, sigma molecules were rarely found in recombination deficient, reca, infected cells. the ...	1983	6359666
requirement of e. coli dna synthesis functions for the lytic replication of bacteriophage p1.	p1 lytic growth was examined in a number of different temperature sensitive mutants of e. coli that affect chromosomal replication. growth was analyzed by measurements of phage burst sizes and specific dna synthesis. efficient p1 growth required each of the bacterial elongation functions dnae (polc), dnaz (sub units of e. coli polymerase iii holoenzyme), and dnag (primase) but was not dependent on the elongation function dnab (mobile promoter). of two initiation functions tested the dnaa functio ...	1983	6359668
generalized transduction between salmonella typhi and salmonella typhimurium by phage j2 and characterization of the j2 plasmid in escherichia coli.	phage j2, a p1-like phage in salmonella typhi, was heteroimmune to phage p1 and existed in the lysogenic state as a plasmid of molecular size 58.6 mdal. the phage j2 plasmid was incompatible with the p1 plasmid (incy group). a j2-sensitive mutant of salmonella typhimurium lt2 was isolated by transduction of j2ap phage into lt2 followed by curing of the prophage. the mutant was used to demonstrate transduction between s. typhi and s. typhimurium by phage j2.	1983	6363617
the molecular genetics of bacteriophage p1.		1983	6364958
coliphage p1 morphogenesis: analysis of mutants by electron microscopy.	we used electron microscopy and serum blocking power tests to determine the phenotypes of 47 phage p1 amber mutants that have defects in particle morphogenesis. eleven mutants showed head defects, 30 showed tail defects, and 6 had a defect in particle maturation (which could be either in the head or in the tail). consideration of previous complementation test results, genetic and physical positions of the mutations, and phenotypes of the mutants allowed assignment of most of the 47 mutations to ...	1983	6834479
studies on the properties of p1 site-specific recombination: evidence for topologically unlinked products following recombination.	bacteriophage p1 encodes its own site-specific recombination system consisting of a site at which recombination takes place called loxp and a recombinase called cre. a number of lambda and plasmid substrates containing two loxp sites have been constructed. using these substrates we have shown both in vivo and in vitro that a fully functional loxp site is composed of no more than 60 bp. in vitro, when an extract containing cre is used, recombination between loxp sites on supercoiled, nicked-circl ...	1983	6220808
replication-control functions block the induction of an sos response by a damaged p1 bacteriophage.	uv-damaged bacteriophage p1 causes an sos response in infected bacteria that can be measured colorimetrically with the aid of a lambda pl-lacz fusion strain of escherichia coli. this response is blocked by a p1 prophage. evidence is offered that the blockage is caused by the concerted action of the incompatibility determinant inca and the immunity (c1 and c4) repressors of the prophage. we suggest that indirect induction of lambda by damaged p1 is caused by the abortive initiation of replication ...	1983	6227794
site-specific recombinational circularization of bacteriophage p1 dna.		1983	6228057
interaction of the bacteriophage p1 recombinase cre with the recombining site loxp.	the interaction between the p1 recombinase protein cre and the dna site at which it acts, loxp, has been studied by using nuclease protection techniques. the region of dna protected by cre against nuclease attack by dnase i or neocarzinostatin is a 34-base-pair (bp) region containing two 13-bp inverted repeats separated by an 8-bp spacer region. these protected sequences have previously been shown to be required for efficient cre-mediated recombination at loxp. the results of the above protectio ...	1984	6230671
effect of bacteriophage p1 lysogeny on lipopolysaccharide composition and the lambda receptor of escherichia coli.	the outer membrane of escherichia coli was altered as a consequence of lysogeny by bacteriophages p1 and p1 cmts. the predominant change was a reduction in the size of lipopolysaccharide to a heptose-deficient form. p1 cmts lysogens were still sensitive to several bacteriophages but were resistant to lambda vir. neither whole cells nor solubilized outer membranes from p1 cmts lysogens were able to inactivate lambda vir, and 32p-labeled lambda vir was unable to adsorb to p1 cmts lysogens. p1 cmts ...	1984	6237098
location and analysis of nucleotide sequences at one end of a putative lac transposon in the escherichia coli chromosome.	a segment of escherichia coli dna that contained a discontinuity of homology with salmonella typhimurium dna was isolated. the segment, 1,430 base pairs long, was derived from one end of the lac "loop," a region of about 12 kilobase pairs of e. coli dna, including the lac operon which has no detectable homology with s. typhimurium dna (k. lampel and m. riley, mol. gen. genet. 186:82-86, 1982). the nucleotide sequence of the 1,430-base-pair segment of dna was determined. the location of the junct ...	1984	6086580
characterization of generalized transducing phage phi w39 heteroimmune to phage p1 in escherichia coli w39.	generalized transducing phage similar to phage p1 in escherichia coli was isolated from e. coli w39, an antigenic test strain of the o121 group. this phage, designated phi w39, was reciprocally heteroimmune to phages p1 and p7, but nonreciprocally heteroimmune to phage d6. transduction experiments using various r plasmids with different molecular weights suggested that phage phi w39 could transduce at least 65 megadaltons dna. as in the case of p1 prophage, phi w39 prophage existed as a plasmid ...	1984	6087089
is30, a new insertion sequence of escherichia coli k12.	three independent spontaneous mutations of prophage p1 affecting the ability of the phage to reproduce vegetatively are due to the insertion of a mobile genetic element, called is30. the same sequence is also carried in the r plasmid nr 1-basel, but not in the parental plasmid nr 1. southern hybridisation study indicates that the escherichia coli k 12 chromosome carries several copies of is30 as a normal resident. is30 is 1.2 kb long and contains unique restriction cleavage sites for bglii, clai ...	1984	6090868
reduction of marker discrimination in transductional recombination.	the recovery of phage p1 mediated transductants varies with the marker selected in a manner which cannot be fully accounted for by dosage differences in the donor gene population. this variation in transduction frequency is due primarily to recombinational discrimination in the recipient cell. we show here that increasing the intracellular level of reca protein, which might be expected to increase the contribution of recf mediated events to recombinant formation, decreases this discrimination sl ...	1984	6090869
construction of tn5 lac, a transposon that fuses lacz expression to exogenous promoters, and its introduction into myxococcus xanthus.	a promoterless trp-lac fusion fragment was inserted near one end of the bacterial transposon tn5 in the correct orientation to fuse lacz gene expression to promoters outside tn5. the resulting transposon, tn5 lac, retains the kanamycin-resistance gene of tn5 and transposes in escherichia coli at 6% the frequency of tn5 to many different sites in a bacteriophage lambda target. expression of beta-galactosidase, the product of the lacz gene, from tn5 lac insertions in phage lambda depends both on i ...	1984	6091110
sn-glycerol-3-phosphate auxotrophy of plsb strains of escherichia coli: evidence that a second mutation, plsx, is required.	sn-glycerol-3-phosphate auxotrophs defective in phospholipid synthesis contain a km-defective sn-glycerol-3-phosphate acyltransferase. detailed genetic analysis revealed that two mutations were required for the auxotrophic phenotype. one mutation, in the previously described plsb locus (sn-glycerol-3-phosphate acyltransferase structural gene), mapped near min 92 on the escherichia coli linkage map. isolation of tn10 insertions cotransducible with the auxotrophy in phage p1 crosses revealed that ...	1984	6094487
bacteriophage p1 carries two related sets of genes determining its host range in the invertible c segment of its genome.	the bacteriophage p1 genome carries an invertible c segment consisting of 3-kb unique sequences flanked by 0.6-kb inverted repeats. host range mutations of p1 have been mapped in the c segment region. p1 derivatives carrying insertions and deletions in the left half of the c segment in one of two orientations termed c(+) do not affect the plaque-forming ability on escherichia coli k12 and e coli c, whereas those having insertions in the right half of the c segment fail to form plaques on these h ...	1984	6100576
the bacteriophage p1 site-specific recombinase cin: recombination events and dna recognition sequences.		1984	6597763
isolation and characterization of regulatory mutations affecting the expression of the guaba operon of escherichia coli k-12.	we isolated strains of escherichia coli k 12 in which the lac structural genes were fused to the structural genes of the guaba operon. these strains were used to isolate regulatory mutations that increased the expression of the guaba operon under normal repressing conditions as compared to the wild type parental fusion strain. three classes of guaba specific regulatory mutations were identified. class i regulatory mutations were trans-acting and unlinked to the guaba operon as shown by bacteriop ...	1984	6387393
the structural gene for amp nucleosidase. mapping, cloning, and overproduction of the enzyme.	a mutant of escherichia coli which contained no detectable amp nucleosidase activity (ec 3.2.2.4) was produced by treatment with nitrosoguanidine and identified by a colorimetric assay for amp nucleosidase in individual colonies from agar plates. conjugation experiments indicated a close linkage between the amp nucleosidase locus (amn) and his. assays for amp nucleosidase in e. coli strains with deletions in the his region established that amn is not located between attp2h and mgl . transduction ...	1984	6327703
site-specific recombination by the bacteriophage p1 lox-cre system. cre-mediated synapsis of two lox sites.	the bacteriophage p1-encoded recombinase cre forms a simple dna-protein complex at the specific recognition site loxp. furthermore, cre is able to mediate a synaptic union of two loxp sites. when two loxp sites are on the same linear dna molecule, cre binds the two sites together to form a circular protein-dna complex. these complexes can be resolved into a linear dna molecule and a closed circular dna molecule, the end products of site-specific recombination.	1984	6333513
bacteriophage p1 site-specific recombination. purification and properties of the cre recombinase protein.	bacteriophage p1 encodes a site-specific recombination system that consists of a site (loxp) at which recombination occurs and a gene, cre, whose protein product is essential for recombination. the loxp-cre recombination event can be studied in greater detail by the use of an in vitro system that efficiently carries out recombination between two loxp sites. this paper presents a purification and characterization of the cre protein (mr = 35,000), which is the only protein required for the in vitr ...	1984	6319400
use of bacteriophage p1 as a vector for tn5 insertion mutagenesis.	infection of a strain lysogenic for bacteriophage p1 cm with p1::tn5 followed by simultaneous selection for the chloroamphenicol resistance associated with the resident prophage and the kanamycin resistance associated with tn5 results in a large number of independent tn5 insertion mutations. this superinfection-selection protocol is a fast, easy, and safe way to isolate null mutations in enteric bacteria without generating unwanted cryptic mutations elsewhere in the genome.	1984	6324677
p1 plasmid replication: replicon structure.	bacteriophage p1 lysogenizes escherichia coli as a unit-copy plasmid. we have undertaken to define the plasmid-encoded elements implicated in p1 plasmid maintenance. we show that a 2081 base-pair fragment of the 90,000 base p1 plasmid confers the capacity for controlled plasmid replication. dna sequence analysis reveals several open reading frames in this fragment. the largest is shown to encode a 32,000 mr protein required for plasmid replication. the corresponding gene, repa, has been identifi ...	1984	6699914
mechanism of strand cleavage and exchange in the cre-lox site-specific recombination system.	the bacteriophage p1 recombinase cre mediates site-specific recombination between loxp sites. the loxp site consists of two 13 base-pair inverted repeats separated by an eight base-pair spacer region. when dna containing the loxp site is incubated with cre, specific cleavages occur within the spacer region, creating a six base-pair staggered cut. the cuts are centered on the axis of dyad symmetry of the loxp site, resulting in a 5' protruding terminus: 5' a decreases t-g-t-a-t-g c 3' t a-c-a-t-a ...	1985	3856690
p1 plasmid replication: multiple functions of repa protein at the origin.	replication functions of a bacteriophage p1 miniplasmid are carried on a 1.2-kilobase pair (kb) segment that can be subdivided into a 245-base pair (bp) replication origin and a 959-bp region that encodes a protein required for replication (repa). the origin region contains five 19-bp direct repeats. by using primer extension and gene-fusion assays, we mapped the promoter of the repa gene within the repeated sequences and showed that the promoter is repressed by repa. regulation of repa synthesi ...	1985	3857601
phage p1 cre-loxp site-specific recombination. effects of dna supercoiling on catenation and knotting of recombinant products.	bacteriophage p1 contains a site-specific recombination system consisting of a site, loxp, and a recombinase protein cre. we have shown that with purified cre protein we can carry out recombination between two loxp sites in vitro. when that recombination occurs between two sites in direct orientation on the same dna molecule, we observed the production of free and catenated circular molecules. in this paper we show that recombination between sites in opposite orientation leads to both knotted an ...	1985	3875731
genetic mapping of nth, a gene affecting endonuclease iii (thymine glycol-dna glycosylase) in escherichia coli k-12.	the nth gene of escherichia coli affects the production of endonuclease iii, a glycosylase-endonuclease that attacks dna damaged by oxidizing agents or by ionizing radiation. an nth insertion mutant and a deletion mutant were studied. nth is located between add and tyrs on the linkage map of e. coli k-12 and was 97% linked to tyrs in a transduction with phage p1.	1985	3886628
expression of the bacteriophage p1 cin recombinase gene from its own and heterologous promoters.	the cin recombinase of bacteriophage p1, a protein that catalyses site-specific dna inversions, has been identified and its structural gene has been cloned under the control of different promoters. one of the dna sequences used for the site-specific recombination, cixl, overlaps with the 3' end of the gene, but we show that the presence of this site does not affect cin gene expression from strong promoters. to assay cin activity we have constructed plasmids that carry antibiotic resistance genes ...	1985	3891516
genetic location of genes encoding enterobacterial common antigen.	a new rff mutation (rff-726) of escherichia coli is described which affects the biosynthesis of the enterobacterial common antigen. this mutation was detected in an rfe-defective strain. a tn10 insertion near the rfe locus was isolated to facilitate further mapping. both mutations rfe and rff were mapped by transduction with bacteriophage p1, giving the gene order ilv rfe rff uvrd mete. the f' factor f14 was able to complement both mutations rfe and rff, whereas the f' factor f16 could complemen ...	1985	3894334
in vivo transfer of chromosomal mutations onto multicopy plasmids by transduction with bacteriophage p1.	a technique is presented by which chromosomal mutations may be efficiently transferred onto chimeric multicopy plasmids in vivo. the technique employs the transduction of plasmids using bacteriophage p1 as vector. the utility of this method was demonstrated by cloning a chromosomal ompr mutation of escherichia coli k-12. the high-frequency transduction of the chimeric plasmid appeared to be dependent on its integration into the chromosome by homologous recombination. the results also suggest tha ...	1985	3913625
internal promoter in the ilvgeda transcription unit of escherichia coli k-12.	segments of the ilvgeda transcription unit have been cloned into the promoter tester plasmid pmc81. this vector contains cloning sites situated upstream of the lacz gene coding for beta-galactosidase. using this method we have quantitatively evaluated in vivo (i) the activity of previously described promoter, pg, preceding ilvg; (ii) the relative activity of pe promoter, previously postulated to be located between ilvg and ilve; and (iii) the effect of the frameshift site present in the wild-typ ...	1985	3917997
endonuclease iii (nth) mutants of escherichia coli.	two strains that overproduce endonuclease iii were found in a colony bank containing hybrid cole1-escherichia coli plasmids. the enzyme was identified in crude extracts by the degradation of partially depyrimidinated dna in the presence of edta, by its sedimentation velocity, and by its associated thymine glycol-dna glycosylase activity. an insertion mutation was produced by cloning the kanamycin-resistance gene of tn5 into the plasmid copy of the nth gene. the mutation was then transferred to t ...	1985	2982160
cloning and complementation analysis of the "frizzy" genes of myxococcus xanthus.	fruiting-body formation in myxococcus xanthus involves the aggregation of cells into raised mounds, where they sporulate. "frizzy" mutants fail to aggregate into mounds, but rather aggregate into "frizzy" filaments (d.r. zusman 1982). the frizzy mutations (frz) were found to be genetically linked. the region of dna carrying the frz genes was cloned in escherichia coli by selecting for the kanamycin resistance element present on a transposon tn5 insertion linked to the frz genes. phage p1 mediate ...	1985	2984519
bacteriophage p1 derivatives unaffected in their growth by a large inversion or by is insertions at various locations.	several plaque-forming phage p1 derivatives carrying dna rearrangements associated with is elements are described. they have is1, is3 and is5 inserted in four distinct locations, all of which are non-essential regions for phage p1 propagation. one derivative carries a genome segment, inverted relative to the one in the p1 wild-type genome, between two inverted copies of is1. the inverted dna segment spans about 23 kb of the 90 kb long p1 genome and it includes the invertible c segment. this phag ...	1985	2985738
crossover sites cix for inversion of the invertible dna segment c on the bacteriophage p7 genome.	the bacteriophage p7 genome contains an invertible dna segment called c which determines its host range. p7 c(+) phages produce plaques on escherichia coli k12. the c segment consists of a 3-kb unique sequence and 0.62-kb inverted repeats of which one carries an internal 0.2-kb deletion. this deletion has been mapped within the right inverted repeat in the c(+) orientation. the crossover sites cix for inversion of the c segment do not map at the inside boundaries of the inverted repeats, as had ...	1985	2998011
formation of small circular dna molecules via an in vitro site-specific recombination system.	the cre-lox site-specific recombination system of bacteriophage p1 has been used to investigate the role of dna flexibility in recombination. we have determined that a minimal distance of 82 bp must separate two loxp sites located on the same dna molecule to allow these sites to undergo intramolecular recombination with one another. as a result of recombination, dna circles as small as 116 bp have been produced. in addition, we have demonstrated that the nuclease bal 31 recognizes distortions in ...	1985	3007297
[isolation of yersinia pestis plasmids with transposon markers].	transposons tn1, tn7, tn9, tn10 have been inserted into each of three known plasmids in yersinia pestis and have been shown to mutagenize the different plasmid genes. the marked plasmids are shown to be transduced by bacteriophage p1 cml clr 100 ts in intrageneric crosses. the genes of 61-65 md plasmid were found to be impaired with high frequencies by tn9 and tn10 insertions blocking the synthesis of fraction i antigen. the genes are also impaired in course of transduction of transposon marked ...	1985	3025677
[mutagenic effect during transduction of (gm-km)r markers of the r323 plasmid in yersinia pestis].	genes of resistance to some aminoglycoside antibiotics from plasmid r323 were transduced by bacteriophage p1 cml clr100 ts in yersinia pestis. the resistance markers were capable of insertion into the chromosome or plasmid in the recipient cells causing the mutagenic effect. the results obtained suggest the transposon nature of plasmid fragment coding for gentamicin-kanamycin resistance.	1985	3025695
site-specific dna inversion is enhanced by a dna sequence element in cis.	a segment of the bacteriophage p1 genome, called the c segment, can be inverted by site-specific recombination; the two different orientations of the invertible segment confer different host ranges to the phage. inversion is catalyzed by the product of the cin gene which is adjacent to one of the crossover sites flanking the c segment. the cin-catalyzed recombination can be measured in trans by using tester plasmids in which inversion switches on antibiotic-resistance genes. we show here that an ...	1985	16593573
is1-dependent generation of high-copy-number replicons from bacteriophage p1 ap cm as a mechanism of gene amplification.	mutant p1 ap cm lysogens were isolated in which the drug resistance genes resident on the plasmid prophage p1 ap cm are amplified by a novel mechanism. the first step required for amplification is is1-mediated rearrangement of the p1 ap cm prophage. the drug resistance genes are amplified from the rearranged p1 ap cm prophage by the formation of a plasmid (p1dr) which contains the two resistance genes. the p1dr plasmid is an independent replicon about one-half the size of p1 ap cm that can be ma ...	1986	3009413
dna inversion in bacteriophage mu: characterization of the inversion site.	gin-mediated site-specific recombination promotes inversion of the g segment of phage mu. the crossover takes place between two 34 bp-long inverted repeat sequences flanking the g segment. we have characterized the inversion site, the target for the site-specific recombination mechanism. an artificial invertible segment was constructed which consists of parts of the invertible segments of mu and phage p1, which in this respect are largely homologous. upon inversion of this hybrid segment the cro ...	1986	3011972
a phage p1 function that stimulates homologous recombination of the escherichia coli chromosome.	recombination between two different defective lacz genes in the escherichia coli chromosome (lac- x lac- recombination) was stimulated 2- to 8-fold by prophage p1, depending on the nature of the phage c1 repressor. the p1 bamhi restriction fragment b8 in a lambda-p1:b8 hybrid phage, stimulated lac- x lac- recombination 90-fold in the absence of p1 repressor. a gene necessary for recombination enhancement, designated ref, was localized to one end of b8. ref expression from lambda-p1:b8 was repres ...	1986	3012538
molecular cloning of the phosphate (inorganic) transport (pit) gene of escherichia coli k12. identification of the pit+ gene product and physical mapping of the pit-gor region of the chromosome.	the pit+ gene, encoding the phosphate (inorganic) transport system of escherichia coli, was isolated from a library of e. coli genes inserted in the cosmid vector phc79. a 25.5-kb chromosomal dna fragment was shown also to carry the gor locus encoding glutathione oxidoreductase. physical mapping placed the two genes about 10 kb apart, confirming bacteriophage p1 mapping of the 77-min region. subcloning and deletion analysis indicated that the entire pit+ gene was located within a 2.2-kb sal1-ava ...	1986	3020381
bacteriophage p1 cre-loxp site-specific recombination. site-specific dna topoisomerase activity of the cre recombination protein.	site-specific recombination in bacteriophage p1 occurs between two loxp sites in the presence of the cre recombination protein. the structure of the 34-base pair loxp site consists of two 13-base pair inverted repeats separated by an 8-base pair spacer region. a mutation in the loxp site has been constructed which deletes one of the internal bases of the spacer region at the axis of dyad symmetry. this mutant loxp site shows a 10-fold reduction in recombination activity with a wild-type site bot ...	1986	3001054
cloning of the vibrio cholerae reca gene and construction of a vibrio cholerae reca mutant.	a recombinant plasmid carrying the reca gene of vibrio cholerae was isolated from a v. cholerae genomic library, using complementation in escherichia coli. the plasmid complements a reca mutation in e. coli for both resistance to the dna-damaging agent methyl methanesulfonate and recombinational activity in bacteriophage p1 transductions. after determining the approximate location of the reca gene on the cloned dna fragment, we constructed a defined reca mutation by filling in an xbai site locat ...	1986	3005236
genetic analysis of myxococcus xanthus and isolation of gene replacements after transduction under conditions of limited homology.	genetic analysis of myxococcus xanthus is greatly facilitated by the ability to introduce cloned dna into m. xanthus to generate gene replacement and merodiploid strains. however, gene replacement strains are difficult to obtain when the region(s) of homology between the cloned dna and the m. xanthus chromosome is limited (less than 1 kilobase). we found that gene replacements can be obtained at an increased frequency by a two-step procedure involving the use of bacteriophage p1 to isolate merod ...	1986	3090023
visualization of rna polymerase bound to r-loop molecules improves electron microscopic analysis of in vitro transcription.	an electron microscope method is described which allows improved analysis of in vitro transcription. transcription complexes are fixed with glutaraldehyde, subjected to r-loop conditions which allow the nascent rna chains to hybridize to the dna templates, and mounted for electron microscopy by a protein-free preparation method. an rna polymerase molecule (or parts of it) associated with only one end of the r-loop identifies the polarity of the transcript, thus determining the origin and directi ...	1986	3316423
the role of the loxp spacer region in p1 site-specific recombination.	the lox-cre site-specific recombination system of bacteriophage p1 is comprised of a site on the dna where recombination occurs called loxp, and a protein, cre, which mediates the reaction. the loxp site is 34 base pairs (bp) in length and consists of two 13 bp inverted repeats separated by an 8 bp spacer region. previously it has been shown that the cleavage and strand exchange of recombining loxp sites occurs within this spacer region. we report here an analysis of various base substitution mu ...	1986	3457367
bacteriophage p1 cre gene and its regulatory region. evidence for multiple promoters and for regulation by dna methylation.	the bacteriophage p1 site-specific recombination system consists of two components, a site, loxp, at which recombination occurs, and a recombinase protein, cre. in this paper, we present the dna sequence of the cre structural gene and its upstream regulatory region. analysis of the sequence indicates: (1) that cre encodes a protein of 343 amino acids; (2) that cre and loxp are separated by a 434 base-pair region that contains a 73 amino acid open reading frame, orf1; and (3) that cre and orf1 ar ...	1986	3486297
localized conversion at the crossover sequences in the site-specific dna inversion system of bacteriophage p1.	the crossover sites for site-specific c inversion consist of imperfect 12 bp inverted repeats with the dinucleotide tt at the center of symmetry. the phage p1 cin recombinase acts not only at these cix sites but also less efficiently at cix-related sequences called quasi-cix sites, cixq. when cixq contains a central dinucleotide tt, crossover occurs in vivo at the 2 bp sequence tt in the normal and the quasi-cix sites. if cixq carries only one t residue, inversion-associated localized conversion ...	1986	3513965
sequence relations among the incy plasmid p15b, p1, and p7 prophages.	electron microscopic analysis of heteroduplex molecules between the 94-kb plasmid p15b and the 92-kb phage p1 genome revealed nine regions of nonhomology, eight substitutions, and two neighboring insertions. overall, the homologous segments correspond to 83% of the p1 genome and 81% of p15b. heteroduplex molecules between p15b and the 99-kb phage p7 genome showed nonhomology in eight of the same nine regions; in addition, two new nonhomologous segments are present and p7 carries a 5-kb insertion ...	1986	3749335
linking-number changes in the dna substrate during cre-mediated loxp site-specific recombination.	we have examined the linking-number changes that occur during phage p1 cre-mediated recombination in vitro between two loxp sites. such recombination reactions can be divided into three types: intramolecular inversion, in which recombination occurs between two loxp sites in opposite orientations on the same dna substrate; intramolecular excision, where recombination occurs between two loxp sites that are in the same orientation on the dna substrate; and intermolecular recombination, which occurs ...	1986	3820304
the c4 gene of phage p1.	the c4 gene of phage p1 has been localized to 335 bp of the p1ecori-9 fragment, within 50 bp of the ecori-9/14 junction. dna sequence analysis of this fragment reveals a single open reading frame of 66 amino acids. the location of two c4 mutations, both of which produce changes in the predicted amino acid sequence in this reading frame, suggests that the reading frame codes for the c4 repressor. a region with high homology to the e. coli promoter consensus sequence is located approximately 50 bp ...	1987	3811234
interaction of the p1c1 repressor with p1 dna: localization of repressor binding sites near the c1 gene.	the c1 repressor of phage p1 was previously shown (b.r. baumstark and j.r. scott, 1980, j. mol. biol. 140, 471-480) to bind specifically to p1bamhi-9, a 1.4-kb fragment that is closely linked to the c1 structural gene and spans the ends of the p1 genetic map. the position of the repressor binding site(s) relative to the ends of the genetic map and the c1 gene was investigated by testing cloned fragments of ecori-7 and bamhi-9 for c1 expression and repressor binding. although sequences in both ba ...	1987	3811241
genetic suppression of a temperature-sensitive groes mutation by an altered subunit of rna polymerase of escherichia coli k-12.	temperature-resistant suppressor mutants were isolated from escherichia coli mutant strain groes131(ts). phage p1-mediated transduction and a two-dimensional gel electrophoretic analysis of cellular proteins indicated that these suppressor mutants carry an additional mutation in either the groel gene or the rpoa gene.	1987	3546264
recognition and cleavage of the bacteriophage p1 packaging site (pac). ii. functional limits of pac and location of pac cleavage termini.	bacteriophage p1 initiates the processive packaging of its dna at a unique site called pac. we show that a functional pac site is contained within a 161 base-pair segment of p1 ecori fragment 20. it extends from a position 71 base-pairs to a position 232 base-pairs from the ecori-22 proximal side of that fragment. the 3' and 5' pac termini are located centrally within that 161 base-pair region and are distributed over about a turn of the dna helix. the dna sequence of the terminus region is show ...	1987	3625770
a mutational analysis of the bacteriophage p1 recombinase cre.	bacteriophage p1 encodes a 38,600 mr site-specific recombinase, cre, that is responsible for reciprocal recombination between sites on the p1 dna called loxp. using in vitro mutagenesis 67 cre mutants representing a total of 37 unique changes have been characterized. the mutations result in a wide variety of phenotypes as judged by the varying ability of each mutant cre protein to excise a lacz gene located between two loxp sites in vivo. although the mutations are found throughout the entire cr ...	1987	3656435
the ban operon of bacteriophage p1. localization of the promoter controlled by p1 repressor.	repression of a strong promoter localized 5' to the p1 ban gene is a prerequisite for cloning the ban operon in the multicopy plasmid pbr325. repression is brought about by the binding of p1 repressor to the operator of the ban operon (heisig, a., severin, i., seefluth, a. k., and schuster, h. (1987) mol. gen. genet. 206, 368-376). binding of rna polymerase in vitro overlaps with the operator and is inhibited by p1 repressor as shown by electron microscopy. the mutant p1 bac, which renders ban e ...	1987	3680265
purification and dna-binding properties of fis and cin, two proteins required for the bacteriophage p1 site-specific recombination system, cin.	an escherichia coli chromosomally coded factor termed fis (factor for inversion stimulation) stimulates the cin protein-mediated, site-specific dna inversion system of bacteriophage p1 more than 500-fold. we have purified fis and the recombinase cin, and studied the inversion reaction in vitro. dna footprinting studies with dnase i showed that cin specifically binds to the recombination site, called cix. fis does not bind to cix sites but does bind to a recombinational enhancer sequence that is ...	1987	3323534
transductional analysis of chromosome replication time.	following transduction of exponentially growing cultures of escherichia coli with phage p1, cells with recombinant phenotype begin to increase in number after an initial lag of about one generation time. we show that transductants for markers located at different positions on the chromosome begin to increase at different times, in reverse order to that in which they are replicated. the period over which this happens is equal in duration to the time taken to replicate the chromosome and we have u ...	1987	3325777
characterization of the binding sites of c1 repressor of bacteriophage p1. evidence for multiple asymmetric sites.	the repressor of bacteriophage p1, encoded by the c1 gene, is responsible for maintaining a p1 prophage in the lysogenic state. in this paper we present: (1) the sequence of the rightmost 943 base-pairs of the p1 genetic map that includes the 5'-terminal 224 base-pairs of the c1 gene plus its upstream region; (2) the construction of a plasmid that directs the production of approximately 5% of the cell's protein as p1 repressor; (3) a deletion analysis that establishes the startpoint of p1 repres ...	1987	3430609
altered phage p1 attachment to strains of escherichia coli carrying the plasmid colv,i-k94.	phages p1vir and p1cmclrf100 failed to form plaques on or multiply in escherichia coli strains carrying the colv,i-k94 plasmid; with p1cmclr100, the effect occurred both with phage from the lytic cycle and with that induced from a lysogen. the effect was on attachment, these p1 phages attaching poorly to colv,i-k94+ strains. this receptor defect appeared to result mainly from the presence of colv-encoded transfer and colicin components in the cells carrying colv,i-k94 and it was specific to this ...	1987	2955078
construction of an ordered overlapping library of bacteriophage p1 dna in phage vector lambda d69.	a library of bacteriophage p1 dna was constructed in the phage vector lambda d69. the dna of some 150 randomly chosen lambda-p1 hybrid phages containing p1 dna fragments 5-10 kb in size was analyzed by restriction endonuclease digestion using enzymes ecori, bglii, and bamhi that cleave p1 dna at known positions on the physical map of p1. approximately one third of the phages contained p1 dna inserts having two or more restriction sites for any one of these enzymes, thus allowing the location of ...	1987	2964385
recognition and cleavage of the bacteriophage p1 packaging site (pac). i. differential processing of the cleaved ends in vivo.	the packaging of bacteriophage p1 dna into viral capsids is initiated at a specific dna site called pac. during packaging, that site is cleaved and at least one of the resulting ends is encapsidated into a p1 virion. we show here that pac is located on a 620 base-pair fragment of p1 dna (ecori-20). when that fragment is inserted into the chromosome of cells that are then infected with p1, packaging of host dna into phage particles is initiated at pac and proceeds down the chromosome, unidirectio ...	1987	3305962
role of the central dinucleotide at the crossover sites for the selection of quasi sites in dna inversion mediated by the site-specific cin recombinase of phage p1.	the crossover sites for cin-mediated inversion consist of imperfect 12 bp inverted repeats with non-palindromic dinucleotides at the center of symmetry. inversion is believed to occur in vivo between the homologous central 2 bp crossover sequences at the inversely repeated crossover sites through introduction of 2 bp staggered cuts and subsequent reciprocal strand exchanges. the site-specific cin recombinase acts not only on the normal crossover sites but also, less efficiently, on quasi crossov ...	1987	3312949
two dna antirestriction systems of bacteriophage p1, dara, and darb: characterization of dara- phages.	bacteriophage p1 is only weakly restricted when it infects cells carrying type i restriction and modification systems even though dna purified from p1 phage particles is a good substrate for type i restriction enzymes in vitro. here we show that this protection against restriction is due to the products of two phage genes which we call dara and darb (dar for defense against restriction). each of the dar gene products provides protection against a different subset of type i restriction systems. t ...	1987	3029954
expression and proteolytic processing of the dara antirestriction gene product of bacteriophage p1.	the dara gene coding for one of the two bacteriophage p1 antirestriction functions is expressed late after infection or induction. the protein is made as a high-molecular-weight soluble precursor. this is proteolytically cleaved to the mature form, which is a structural component of the phage head. defective mutants of the phage have been found in which the synthesis of gpdara is normal but processing does not take place. these mutations all map to the same region of the p1 genome and we propose ...	1987	3029955
a cloned dna fragment from bacteriophage p1 enhances is2 insertion.	a 1.75 kb dna segment of the bacteriophage p1 genome is known to serve as a preferred target for is2 insertions. the presence of this fragment in a plasmid expressing the galk gene dramatically increases the proportion of is2 insertions among spontaneous galk- mutants. subfragments from two different parts of the 1.75 kb segment independently stimulate is2 insertion, while another subfragment does not. in the plasmids studied is2 elements not only insert into the cloned p1 fragment but also into ...	1987	3035338
replication of mini-p1 plasmid dna in vitro requires two initiation proteins, encoded by the repa gene of phage p1 and the dnaa gene of escherichia coli.	we have developed an in vitro dna-replication system that replicates exogenously added mini-p1 plasmid dna. the system consists of purified p1 repa protein and a partially purified mixture of escherichia coli replication proteins. it is essentially the same as that described for the replication of oric plasmid dna [fuller, r.s., kaguni, j.m. & kornberg, a. (1981) proc. natl. acad. sci. usa 78, 7370-7374]. mini-p1 dna replication requires the e. coli dnaa initiation protein in addition to the p1 ...	1987	3035546
transposition of tn4551 in bacteroides fragilis: identification and properties of a new transposon from bacteroides spp.	tn4551, a clindamycin resistance (ccr) transposon from the r plasmid pbi136, was cloned onto an escherichia coli-bacteroides shuttle vector which could replicate normally in e. coli but was maintained unstably in bacteroides fragilis. to aid in cloning and to ensure maintenance of tn4551 in e. coli, a kanamycin resistance determinant (kmr) was inserted in the transposon. the transposon-bearing shuttle vector pfd197 was transformed into b. fragilis 638, and putative insertions of tn4551::kmr were ...	1987	3038840
multiple repressor binding sites in the genome of bacteriophage p1.	after digestion of bacteriophage p1 dna with ecori in the presence of p1 repressor, 6 repressor binding sites were identified in 5 of 26 ecori fragments. binding sites were localized by the decreased mobility of dna fragment-repressor complexes during electrophoresis and by dnase protection ("footprinting") analysis. the repressor binding sites, or operators, comprise a 17-base-pair-long consensus sequence lacking symmetrical elements. three operators can be related to known genes, whereas the f ...	1987	3039493
localization of stx, a determinant essential for high-level production of shiga toxin by shigella dysenteriae serotype 1, near pyrf and generation of stx transposon mutants.	hfr strains of shigella dysenteriae serotype 1 were constructed by transient integration of an rp4 plasmid derivative carrying transposon tn501 into the shigella chromosome through tn501-mediated cointegration. the hfr strains were mated with escherichia coli k-12 recipients carrying various auxotrophic markers, and e. coli recombinants which had received prototrophic shigella genes were selected. some of the e. coli transconjugants produced high levels of a cytotoxin which was neutralized by bo ...	1987	3040592
isolation and characterization of intermediates in site-specific recombination.	cre, the site-specific recombinase from bacteriophage p1, catalyzes a recombination reaction between specific dna sequences designated as lox sites. the breakage and rejoining of partners during this recombination process must be highly concerted because it has not been possible to detect intermediates of the reaction with wild-type cre. several mutant cre proteins have been isolated that produce significant amounts of a possible intermediate product of the recombination reaction. the product ha ...	1987	2821547
p1 plasmid replication requires methylated dna.	plasmids driven by the plasmid replication origin of bacteriophage p1 cannot be established in escherichia coli strains that are defective for the dna adenine methylase (dam). using a composite plasmid that has two origins, we show that the p1 origin cannot function even in a plasmid that is already established in a dam strain. an in vitro replication system for the p1 origin was developed that uses as a substrate m13 replicative-form dna containing the minimal p1 origin. the reaction mixture co ...	1987	2826133
growth-rate-dependent expression and cloning of gnd alleles from natural isolates of escherichia coli.	6-phosphogluconate dehydrogenase (6pgd), encoded by gnd, is highly polymorphic among isolates of escherichia coli form natural populations. as a means of characterizing the growth-rate-dependent regulation of the level of 6pgd, five gnd alleles, including the e. coli b/r allele, were crossed into e. coli k-12 with bacteriophage p1. in each of the isogenic strains, the level of 6pgd was two- to threefold higher in cells grown on glucose than in cells grown on acetate. the level of enzyme activity ...	1988	2826398
the c1 repressor of bacteriophage p1. isolation and characterization of the repressor protein.	the c1 repressor gene of bacteriophage p1 is located on p1 dna ecori fragment 7 (sternberg, n. (1979) virology 96, 129-142). subfragments of p1 dna ecori fragment 7 were cloned into expression vectors, and the c1 repressor protein from p1 wild-type phage and a revertant of a temperature-sensitive repressor mutant were overproduced in escherichia coli and purified to near-homogeneity. the decreased electrophoretic mobility of p1 dna bamhi fragment 9 in the presence of appropriate protein fraction ...	1988	2826478
uncoupling of the recombination and topoisomerase activities of the gamma delta resolvase by a mutation at the crossover point.	in several well-characterized site-specific recombination systems it has been shown that, for efficient recombination, the two recombining sites must have identical dna sequences across the region between the staggered points of exchange. the precise dna sequence of this overlap region, however, appears to be of little importance (with the exception of one position in the loxp site of bacteriophage p1 (ref. 6]. in this report we characterize a mutant recombination site for the site-specific reco ...	1988	2833710
type iii dna restriction and modification systems ecop1 and ecop15. nucleotide sequence of the ecop1 operon, the ecop15 mod gene and some ecop1 mod mutants.	this paper presents the nucleotide sequence of the mod-res operon of phage p1, which encodes the two structural genes for the ecop1 type iii restriction and modification system. we have also sequenced the mod gene of the allelic ecop15 system. the mod gene product is responsible for binding the system-specific dna recognition sequences in both restriction and modification; it also catalyses the modification reaction. a comparison of the two mod gene product sequences shows that they have conserv ...	1988	2837577
development of an auxotrophic oral live shigella flexneri vaccine.	an oral live attenuated shigella flexneri vaccine candidate strain was constructed by making it auxotrophic and dependent on aromatic metabolites not available in mammalian tissues. an arod gene of escherichia coli k12 strain nk 5131, inactivated by insertion in it of the tn 10 transposon, was transduced using phage p1 into a virulent s. flexneri serotype y strain (sfl 1) isolated from a patient with bacillary dysentery. one of the transductant strains sfl 114 was found to invade hela cells in v ...	1988	2838986
site-specific dna recombination in mammalian cells by the cre recombinase of bacteriophage p1.	the cre protein encoded by the coliphage p1 is a 38-kda protein that efficiently promotes both intra- and intermolecular synapsis and recombination of dna both in escherichia coli and in vitro. recombination occurs at a specific site, called lox, and does not require any other protein factors. the cre protein is shown here also to be able to cause synapsis of dna and site-specific recombination in a mammalian cell line. a stable mouse cell line was established that expresses the cre protein unde ...	1988	2839833
structural and functional analysis of tn4430: identification of an integrase-like protein involved in the co-integrate-resolution process.	the 4149-bp transposon tn4430 from bacillus thuringiensis is delineated by 38-bp inverted repeats and codes for a 113-kd protein that shares homology with the transposases (tnpa) of tn3, tn21 and tn501. through transpositional recombination, this protein generates the formation of co-integrates between both donor and target replicons, with duplication of tn4430 molecules. these features are characteristic of transposons of the tn3 family (class ii elements). the second step of the transposition ...	1988	2842151
participation of escherichia coli integration host factor in the p1 plasmid partition system.	stable maintenance of the plasmid prophage of bacteriophage p1 requires the p1 parb protein, which acts on a dna site termed pars. fractionation of extracts from escherichia coli cells overproducing parb revealed that a host factor, in addition to parb, is required to observe maximal binding to pars, as detected by a nitrocellulose filter retention assay. two observations indicated that this factor is e. coli integration host factor (ihf): purified ihf substituted specifically for host factor fr ...	1988	2842786
requirement of the escherichia coli dnaa gene function for integrative suppression of dnaa mutations by plasmid r 100-1.	the phenotype of escherichia coli dnaa missense and nonsense mutations was integratively suppressed by plasmid r100-1. the suppressed strains, however, could not survive when the dnaa function was totally inactivated. this was demonstrated by the inability of replacing the dnaa allele in the suppressed strain by a dnaa::tn10 insertion using phage p1-mediated transduction. when the intact dnaa+ allele was additionally supplied by a specialized transducing phage, lambda imm21 dnaa+, which integrat ...	1988	2851703
control of cell division by sex factor f in escherichia coli. iii. participation of the groes (mopb) gene of the host bacteria.	cell division of f+ bacteria is coupled to dna replication of the f plasmid. two plasmid coded genes, leta (ccda) and letd (ccdb) are indispensable for this coupling. to investigate bacterial genes that participate in this coupling, we attempted to identify the target of the division inhibitor (the letd gene product) of the f plasmid. two temperature-sensitive growth defective mutants were screened from bacterial mutants that escaped the letd product growth inhibition that occurs in hosts carryi ...	1988	2901493
transduction of escherichia coli in soil.	bacteriophage p1-mediated generalized transduction of escherichia coli k-12 was assessed in nonsterile soil. auxotrophic recipient cells (thr- leu- thi- rpsl) were incubated in a sandy and a silty clay loam soil, and the transducing phage lysates from prototrophic strains carrying transposon 10(tn10) in either pure or arol regions were added. at intervals, the bacterial populations derived from the soils were plated on selective-differential media to enumerate prototrophic (thr+, leu+, or tcr) t ...	1988	3042116
transduction of escherichia coli by bacteriophage p1 in soil.	transduction of escherichia coli w3110(r702) and j53(rp4) (10(4) to 10(5) cfu/g of soil) by lysates of temperature-sensitive specialized transducing derivatives of bacteriophage p1 (10(4) to 10(5) pfu/g of soil) (p1 cm cts, containing the resistance gene for chloramphenicol, or p1 cm cts::tn501, containing the resistance genes for chloramphenicol and mercury [hg]) occurred in soil amended with montmorillonite or kaolinite and adjusted to a -33-kpa water tension. in nonsterile soil, survival of i ...	1988	3046491
d-arabinose metabolism in escherichia coli b: induction and cotransductional mapping of the l-fucose-d-arabinose pathway enzymes.	d-arabinose is degraded by escherichia coli b via some of the l-fucose pathway enzymes and a d-ribulokinase which is distinct from the l-fuculokinase of the l-fucose pathway. we found that l-fucose and d-arabinose acted as the apparent inducers of the enzymes needed for their degradation. these enzymes, including d-ribulokinase, appeared to be coordinately regulated, and mutants which constitutively synthesized the l-fucose enzymes also constitutively synthesized d-ribulokinase. in contrast to d ...	1988	3056899
the cyclization of linear dna in escherichia coli by site-specific recombination.	the efficiency with which linearized plasmid dna can transform competent escherichia coli can be significantly increased by use of the cre-lox site-specific recombination system of phage p1. linear plasmid molecules containing directly repeated loxp sites (lox2 plasmids) are cyclized in cre+ e. coli strains after introduction either by transformation or by mini-mu transduction. exonuclease v activity of the recbc enzyme inhibits efficient cyclization of linearized lox2 plasmids after transformat ...	1988	3063605
packaging of transducing dna by bacteriophage p1.	p1 transduces bacterial chromosomal markers with widely differing frequencies. we use quantitative southern hybridisations here to show that, despite this, most markers are packaged at similar levels. exceptions are a group of markers near 2 min and another at 90 min which seem to be packaged at levels two- to threefold higher. we thus conclude that certain marker frequency variations in transduction can be explained by differences in packaging level, but that most cannot. the limited range in p ...	1988	3063949
sequence and deletion analysis of the recombination enhancement gene (ref) of bacteriophage p1: evidence for promoter-operator and attenuator-antiterminator control.	the ref gene of bacteriophage p1 stimulates recombination between two defective lacz genes in the escherichia coli chromosome (lac x lac recombination) and certain other reca-dependent recombination processes. we determined the dna sequence of the 5' portion of the ref gene and tested various regions for functionality by inserting dna fragments lacking increasing amounts of 5' sequence into plasmid and lambda phage vectors and measuring the ability of the constructs to stimulate lac x lac recomb ...	1988	3170487
characterization of the phage p1 dam gene.		1988	3248723