the ecor124 and ecor124/3 restriction and modification systems: cloning the genes.the escherichia coli plasmid r124 codes for a type i restriction and modification system ecor124 and carries genetic information, most probably in the form of a "silent copy," for the expression of a different r-m specificity r124/3. characteristic dna rearrangements have been shown to accompany the switch in specificity from r124 to r124/3 and vice versa. we have cloned a 14.2-kb hindiii fragment from r124 and shown that it contains the hsdr, hsdm, and hsds genes which code for the ecor124 r-m ...19853006102
restriction endonucleases r.ecoki and r.ecor124i are probably located in different environments within the bacterial cell.we describe the phenomenon of a transient state of r124i restriction deficiency after long-term storage of the e. coli[pcp1005] strain at 4 degrees c, or after growth of the culture in synthetic m9 medium with the nonmutagenic solvent dimethyl sulfoxide. the unusual high reversion from the r+ 124 to the r- 124 phenotype was observed only in e. coli strain transformed with the high-copy number plasmid pcp1005 carrying ecor124i hsdr, m and s genes cloned, but not with strains carrying the natural ...19947959434
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