title: Deoxyribonucleic acid-cytosine methylation by host- and plasmid-controlled enzymes.
abstract: Deoxyribonucleic acid (DNA)-cytosine methylation specified by the wild-type Escherichia coli K 12 mec+ gene and by the N-3 drug resistance (R) factor was studied in vivo and in vitro. Phage lambda and fd were propagated in the presence of L-[methyl-3H]methionine in various host bacteria. The in vivo labeled DNA was isolated from purified phage and depurinated by formic acid-diphenylamine treatment. The resulting pyrimidine oligonucleotide tracts were separated according to size and base composition by chromatography on diethylaminoethyl-cellulose in 7 M urea at pH 5.5 and 3.5, respectively. The distribution of labeled 5-methylcytosine in DNA pyrimidine tracts was identical for phage grown in mec+ and mec minus (N-3) cells. For phage lambda the major 5-methylcytosine containing tract was the tripyrimidine, C2T; for both fd-mec minus (N-3) DNA and fd-mec+DNA, C2T was the sole 5-methylcytosine-containing tract. When various lambda DNAs were methylated to saturation in vitro by crude extracts from mec+ and mec minus (N-3) cells, the extent of cytosine methylation was the same. This is in contrast to in vivo methylation where lambda-mec minus (N-3) DNA contains twice as many 5-methylcytosines per genome as lambda-mec+ DNA. Therefore, we suggest that the K12 met+ cytosine methylase and the N-3 plasmid modification methylase are capable of recognizing the same nucleotide sequences, but that the in vivo methylation rate is lower in mec+ cells.
mesh_terms: D000818:Animals; D001483:Base Sequence; D002417:Cattle; D002474:Cell-Free System; D002848:Chromatography, DEAE-Cellulose; D003090:Coliphages; D003596:Cytosine / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism*; D004247:DNA / Q000032:analysis / Q000378:metabolism; D004267:DNA Viruses; D004279:DNA, Viral / Q000032:analysis / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D005111:Extrachromosomal Inheritance; D008715:Methionine / Q000378:metabolism*; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism*; D011743:Pyrimidines / Q000032:analysis; D013950:Thymus Gland; D014316:Tritium
chemical_list: D004279:DNA, Viral; D011743:Pyrimidines; D014316:Tritium; D003596:Cytosine; D004247:DNA; D008715:Methionine; D008780:Methyltransferases