DNA-methylating activity of mycobacteria

The methylating activity of the four mycobacterium strains Mycobacterium phlei, Mycobacterium smegmatis strain Butyricum, Mycobacterium smegmatis strain Rabinowitz, lysogenic Mycobacterium smegmatis strain Rabinowitz was studied in vitro. All the four strains were found to have methylating activity; enzyme containing extracts of M. smegmatis strain Butyricum and M. phlei showed a stronger activity than those of M. smegmatis strain Rabinowitz and the lysogenic Rabinowitz strain. The methylases of all the four strains methylated the adenine and cytosine residues of the acceptor DNA-forming 5-methyl-cytosine and 6-methyl-aminopurine. The mycobacterial DNAs were methylated by the corresponding mycobacterial methylases in vitro only to 25-30% as compared to the methylation on phage Sd-DNA. This is comparable with the low in vivo methylation of mycobacterial DNAs. The kinetics of methylation indicated a low non-specific nuclease content of the mycobacterium cells.