Methylated nucleic acid bases in Mycobacterium and mycobacteriophage DNA.

Methylated bases of the DNA of two mycobacteria (Mycobacterium phlei and Mycobacterium smegmatis var. butyricum) and two mycobacteriophages (Phage phlei and Phage butyricum) have been studied. In both the bacterial and the phage DNAs 5-methyl-cytosine and 6-methyl-aminopurine could be detected. Using L-(methyl-H3)-methionine as methyl donor not only the methylated bases of bacterium and phage DNA proved to be radioactive, but also the non-methylated purine residues and thymine. Possible pathways of this phenomenon are discussed.