Methylation Pattern of Lambda Deoxyribonucleic Acid

Abstract

Deoxyribonucleic acid (DNA) extracted from phage λ grown on Escherichia coli K-12 strain W4032 had 113 ± 10 5-methylcytosine residues and 215 ± 20 6-methyl adenine residues per genome, as determined by three independent methods. These methylated nucleotides were distributed equally among the two strands of λ DNA. Shearing of double-stranded DNA to half-length fragments revealed a slight deficiency of 5-methyl cytosine in the 55% guanine plus cytosine half. Shearing the DNA to fragments of smaller length showed that the distribution of methylated nucleotides along the double helix was uniform with the exception of an undermethylated fragment arising from the center of the λ DNA molecule. The implication of these results for the function of methylated nucleotides in the λ DNA molecule is discussed.