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structure and function of the nun gene and the immunity region of the lambdoid phage hk022.the immunity region of the lambdoid phage, hk022, has been sequenced. the hk022 repressor gene, its cognate operators and promoters, and several early phage genes can be discerned. the overall design of the immunity region resembles that of other lambdoid phages. the location of the hk022 nun gene, whose product excludes superinfecting lambda by terminating transcription at (or near) the lambda nut sites, is analogous to that of gene n in lambda. nun is preceded by sequences similar to the lambd ...19892760929
a zinc-binding region in the beta' subunit of rna polymerase is involved in antitermination of early transcription of phage hk022.antitermination of early transcription in phage hk022 requires no virus-encoded proteins and thus differs from antitermination by other lambdoid phages. it does require cis-acting phage sequences, which may be analogous to the lambdoid nut sites. to identify host proteins involved in antitermination, we isolated 14 escherichia coli mutants that are specifically blocked in hk022 growth. the mutations are located in the rpoc gene, which encodes the beta' subunit of rna polymerase. each mutation al ...19957752239
identification of functional regions of the nun transcription termination protein of phage hk022 and the n antitermination protein of phage lambda using hybrid nun-n genes.phages lambda and hk022 express proteins n and nun, respectively, each of which acts with a number of escherichia coli host nus factors at lambda nut rna sites, to influence transcription elongation. the lambda nut sites, nearly identical sequences located downstream of the early promoters, pl and pr, were first identified as cis-acting signals required for the action of n in forming termination-resistant transcription complexes. surprisingly, the nun protein, resembling n and expressed by anoth ...19968632463
transcription antitermination: the lambda paradigm updated.coliphage lambda employs systems of transcription termination and antitermination to regulate gene expression. early gene expression is regulated by the phage-encoded n protein working with a series of escherichia coli proteins, nus, at rna sites, nut, to modify rna polymerase to a termination-resistant form. expression of lambda late genes is regulated by the phage-encoded q antitermination protein. q, which appears to use only one host factor, acts at a dna site, qut, to modify rna polymerase ...19958709839
escherichia coli nusa is required for efficient rna binding by phage hk022 nun protein.the nun protein of phage hk022 is an rna binding protein of the arginine-rich motif family. nun binds the phage lambda boxb rna sequence (boxb) on nascent lambda transcripts and arrests transcription elongation. binding to boxb is inhibited by zn2+ and stimulated by the escherichia coli nusa protein. deletion of the nun c-terminal region enhances boxb binding and makes it independent of zn2+ and nusa. the c terminus of nun thus appears to interfere with the n-terminal rna binding motif. nusa rel ...19989465052
mutations affecting cooperative dna binding of phage hk022 ci repressor.cooperative protein-dna interactions play critical roles in gene regulation in all organisms. among the best-studied cooperative interactions is that of phage lambda repressor, which binds cooperatively to two adjacent operators. similar cooperative interactions are also shown by several other lambdoid phage repressors, including hk022 ci repressor, which we study here. this protein has a much higher degree of cooperativity than seen with lambda repressor, and previous evidence has suggested tha ...19989636698
site-specific recombination in mammalian cells expressing the int recombinase of bacteriophage hk022.the int gene of bacteriophage hk022, coding for the integrase protein, was cloned in a mammalian expression vector downstream of the human cytomegalovirus (cmv) promoter. green monkey kidney cells (cos-1) and mouse embryo fibroblast cells (nih3t3) transiently transfected with the recombinant plasmid express the integrase protein. co-transfection of this plasmid with reporter plasmids for site-specific recombination and pcr analyses show that the integrase promotes site-specific integration as we ...199910532317
a spring-loaded state of nusg in its functional cycle is suggested by x-ray crystallography and supported by site-directed mutants.transcription factor nusg is present in all prokaryotes, and orthologous proteins have also been identified in yeast and humans. nusg contains a 27-residue kow motif, found in ribosomal protein l24 where it interacts with rrna. nusg in escherichia coli (ecnusg) is an essential protein and functions as a regulator of rho-dependent transcription termination, phage lambda n and rrna transcription antitermination, and phage hk022 nun termination. relative to ecnusg, aquifex aeolicus nusg (aanusg) an ...200312600194
bacteriophage hk022 nun protein: a specific transcription termination factor that excludes bacteriophage lambda. 200314712713
a conserved zinc binding domain in the largest subunit of dna-dependent rna polymerase modulates intrinsic transcription termination and antitermination but does not stabilize the elongation complex.an evolutionarily conserved zinc-binding motif is found close to the amino terminus of the largest subunits of dna-dependent rna polymerases from bacteria, archaea, and eukaryotes. in bacterial rna polymerase, this motif, the zinc binding domain, has been implicated in protein-dna interactions that stabilize the transcription elongation complex and that occur downstream of the catalytic center. here, we show that this view is incorrect, and instead, the zinc binding domain interacts with product ...200415351641
site-specific recombination in the cyanobacterium anabaena sp. strain pcc 7120 catalyzed by the integrase of coliphage hk022.the integrase (int) of the lambda-like coliphage hk022 catalyzes the site-specific integration and excision of the phage dna into and from the chromosome of its host, escherichia coli. int recognizes two different pairs of recombining sites attp x attb and attl x attr for integration and excision, respectively. this system was adapted to the cyanobacterium anabaena sp. strain pcc 7120 as a potential tool for site-specific gene manipulations in the cyanobacterium. two plasmids were consecutively ...200919429625
two structurally independent domains of e. coli nusg create regulatory plasticity via distinct interactions with rna polymerase and regulators.nusg is a conserved regulatory protein that interacts with elongation complexes (ecs) of rna polymerase, dna, and rna to modulate transcription in multiple and sometimes opposite ways. in escherichia coli, nusg suppresses pausing and increases elongation rate, enhances termination by e. coli rho and phage hk022 nun protein, and promotes antitermination by lambdan and in ribosomal rna operons. we report nmr studies that suggest that e. coli nusg consists of two largely independent n- and c-termin ...200919500594
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