DNA methyltransferase of Bacillus subtilis Marburg: purification, properties and further evidence of specificity.

Bacillus subtilis Marburg strain displays DNA methyltransferase activity. This enzyme, M.BsuM, methylates cytosine in the sequence 5'-YTCGAR-3' (Y = pyrimidine; R = purine). M.BsuM was purified from the exponentially growing cells of B. subtilis 168M. This enzyme (45 +/- 1 kDa) is monomeric and recognizes only double-stranded DNA. It is inhibited partially by Mg2+, Mn2+ ions and spermidine and almost totally by sodium dodecyl sulfate, urea and agarose. This enzyme methylates specifically the three methylatable sites of the plasmid pBM3. Relaxation of specificity ('star' activity) was observed in the presence of organic solvents. A very low amount of M.BsuM was obtained in the standard Marburg strain. To obtain sufficient enzyme attempts are being made to clone the M.BsuM gene in Escherichia coli by using a constructed plasmid (pBM14) vector. Only one transformant containing a 3-kb insert and showing a low level of expression, was obtained.