IDENTIFICATION OF A DNA CYTOSINE METHYLTRANSFERASE GENE IN CONJUGATIVE TRANSPOSON TN5252

The nucleotide sequence of the 3.5-kb right junction fragment of the s treptococcal conjugative transposon Tn5252 was obtained. The DNA fragm ent was found to carry four putative genes one of which displayed a hi gh degree of similarity to prokaryotic SC-cytosine methyltransferases carrying multiple sequence specificities. No cognate endonuclease gene was detected in the sequenced DNA. Purified methylase polypeptide syn thesized in a T7 promoter-controlled overexpression system was found t o lack methylase activity while the cell extracts of host cells contai ning the recombinant plasmid carrying the methylase gene were active. In vivo mutations in the methylase gene did not seem to affect the tra nsferability of the element. (C) 1998 Academic Press.