Comparative Study of the M.BstF5I-1 and M.BstF5I-3 DNA Methyltransferases from the Bacillus stearothermophilus F5 Restriction–Modification System

The BstF5I restriction–modification system from Bacillus stearothermophilus F5, unlike all known restriction–modification systems, contains three genes encoding DNA methyltransferases. In addition to revealing two DNA methylases responsible for modification of adenine in different DNA strands, it has been first shown that one bacterial cell has two DNA methylases, M.BstF5I-1 and M.BstF5I-3, with similar substrate specificity. The boundaries of the gene for DNA methyltransferase M.BstF5I-1 have been verified. The bstF5IM-1 gene was cloned in pJW and expressed in Escherichia coli. Homogeneous samples of M.BstF5I-1 and M.BstF5I-3 were obtained by chromatography with different sorbents. The main kinetic parameters have been determined for M.BstF5I-1 and M.BstF5I-3, both modifying adenine in the recognition site 5"-GGATG-3".