DNA METHYLATION IN MYCOBACTERIA - ABSENCE OF METHYLATION AT GATC (DAM) AND CCA TGG (DCM) SEQUENCES/

The presence of 6-methyladenine and 5-methylcytosine at Dam (GATC) and Dcm (CCA/TGG) sites in DNA of mycobacterial species was investigated using isoschizomer restriction enzymes. In all species examined, Dam a nd Dcm recognition sequences were not methylated indicating the absenc e of these methyltransferases. On the other hand, high performance liq uid chromatographic analysis of genomic DNA from Mycobacterium smegmat is and Mycobacterium tuberculosis showed significant levels of 6-methy ladenine and 5-methylcytosine suggesting the presence of DNA methyltra nsferases other than Dam and Dcm. Occurrence of methylation was also e stablished by a sensitive genetic assay.