title: Isolation of a mutant of Escherichia coli defective in cytosine-specific deoxyribonucleic acid methylase activity and in partial protection of bacteriophage lambda against restriction by cells containing the N-3 drug-resistance factor.
abstract: A mutant (designated mec(-)) of Escherichia coli F(+) 100 endo I(-)su(+) r(K) (-)m(K) (+) has been isolated which is defective in cytosine-specific deoxyribonucleic acid (DNA) methylase activity. The DNA of this mutant, as well as the DNA of phages lambda and fd propagated in it, is virtually devoid of 5-methyl-cytosine (MeC); in contrast, the mutation has no significant effect on the level of N(6)-methyladenine in DNA. Phage lambda grown on the mec(-) mutant is more strongly restricted by N-3-containing cells than is lambda grown on the mec(+) parent. These results suggest that methylation of certain cytosine residues by the E. coli K-12 enzyme partially protects lambda DNA from either the N-3 restriction nuclease or against secondary degradation subsequent to N-3-specific degradation. Analysis of the MeC level in viral and cellular DNA obtained from mec(+), mec(+) (m(N3) (+)), and mec(-) (m(N3) (+)) strains has led to the conclusion that the R-factor controlled DNA-cytosine methylase may be capable of methylating a sequence(s) which is a substrate for the K-12 enzyme.
mesh_terms: D000225:Adenine / Q000032:analysis / Q000378:metabolism; D000476:Alkanesulfonates; D003090:Coliphages / Q000032:analysis / Q000254:growth & development*; D003596:Cytosine / Q000032:analysis; D004269:DNA, Bacterial / Q000032:analysis; D004279:DNA, Viral / Q000032:analysis; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000032:analysis / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification*; D008715:Methionine / Q000378:metabolism; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism*; D009153:Mutagens; D009154:Mutation; D014316:Tritium
chemical_list: D000476:Alkanesulfonates; D004269:DNA, Bacterial; D004279:DNA, Viral; D009153:Mutagens; D014316:Tritium; D003596:Cytosine; D008715:Methionine; D008780:Methyltransferases; D000225:Adenine