Methylated guanine derivative as a minor base in the DNA of phage DDVI Shigella disenteriae

Abstract

7-Methylguanine has been identified in the DNA of phage DDVI, which replicates in Escherichia coli B cells. The amount of this minor base is 0.27 mol per 100 mol of nucleotides. In the DNA of DDVI phage there is no 6-methylaminopurine which is usually a minor component in the DNA of E. coli B and phage T2, yet the DNA of DDVI phage is readily methylated during incubation in vitro with the B-specific methylase and adenosyl[3H]methionine with the label found only in 6-methylaminopurine. An extract of E. coli B cells infected with DDVI phage showed activity of a novel methylase which transfers the [3H]methyl group from S-adenosylmethionine to guanine, leading to the appearance of 7-methylguanine in the acceptor DNA.