title: Deoxyribonucleic acid modification by intermediate-type modification mutants of Escherichia coli K-12 and B.
abstract: The modification of bacteriophages grown on r-m+/- restriction and modification mutants of Escherichia coli K-12 or B appears to be related to the number of restriction-specific sites in the viral genome. Bacteriophage fd and its mutant U1 fd, which carry two and one B-specific sites, respectively, are not modified in vivo by rB-mB+/- mutant strains. In vitro treatment of fd RF-B+/- deoxyribonucleic acid (DNA) or U1 fd RF-B+/- DNA by endo R-Eco B results in cleavage of the substrate DNA. Lambda bacteriophage, after growth in r-m+/- mutant host strains (lambda-K+/- or lambda-B+/-), is partially protected from in vivo degradation by wild-type homospecific strains. Its efficiency of plating on these strains is approximately 10(-2). However, a hybrid phi80-lambda phage which carries only one K-specific site (sklambda-1) is not modified by rK-mK+/- strains. Labeled DNAs from lambda-B+/- and lambda-K+/- phages were used as substrates for endo R-Eco B and endo R-Eco K nucleases. Zonal centrifugation analysis of the products of the reactions indicate that rK-mK+/- mutants do not protect lambda DNA from in vitro degradation by endo R-Eco K. In contrast, rB-mB+/- mutants appear to partially protect lambda DNA from attack by endo R-Eco B.
mesh_terms: D002474:Cell-Free System; D003090:Coliphages / Q000254:growth & development* / Q000378:metabolism; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype; D014779:Virus Replication
chemical_list: D004279:DNA, Viral; D004262:DNA Restriction Enzymes