title: Partially deficient methylation of cytosine in DNA at CCATGG sites stimulates genetic recombination of bacteriophage lambda.
abstract: Lambda bacteriophages grown on arl mutants of Escherichia coli ("Arl-" phages) display intermediate levels of cytosine methylation: less 5-methylcytosine (m5C) than phages grown on wild-type bacteria ("Arl+" phages) but more than phages grown on dcm mutants, and thus lacking the methylated sequences (Cm5CATGG) characteristic of E. coli K-12 bacteria ("Dcm-" phages). "Arl-" phages are one twelfth as resistant to Eco RII restriction (recognition site CCATGG) as "Arl+" phages, but 40-fold more resistant than "Dcm-" phages. Chromatographic analyses show the 5-methylcytosine content of "Arl-" DNA to be one third that of "Arl+" DNA. Altered cytosine methylation frequency correlates with two previously described properties of "Arl-" phages, increased genetic recombination and unusual sensitivity of phage DNA to endonuclease S1, which are absent in phages grown on dcm or dcm arl bacteria. Methylated/unmethylated heteroduplex DNA prepared in vitro (one strand from Eco RII-modified phages/one from "Dcm-" phages) is highly recombinogenic but not S1-sensitive. We hypothesize that hemimethylated CCATGG sites in "Arl-" DNA are necessary and sufficient for enhanced recombination, and necessary but not sufficient for S1 sensitivity.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics* / Q000254:growth & development; D001483:Base Sequence; D003596:Cytosine / Q000378:metabolism*; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D004262:DNA Restriction Enzymes / Q000494:pharmacology; D004279:DNA, Viral / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific; D004720:Endonucleases / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology; D008745:Methylation; D009154:Mutation; D011995:Recombination, Genetic; D015719:Single-Strand Specific DNA and RNA Endonucleases
chemical_list: D004279:DNA, Viral; D003596:Cytosine; D004248:DNA (Cytosine-5-)-Methyltransferases; D004720:Endonucleases; D004262:DNA Restriction Enzymes; C046545:CCWGG-specific type II deoxyribonucleases; D015252:Deoxyribonucleases, Type II Site-Specific; D015719:Single-Strand Specific DNA and RNA Endonucleases