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The Streptococcus faecalis ND547 and Bacillus stearothermophilus 19 genes that code for DNA methyltransferases (MTases, M.) of restriction–modification (RM) systems with the same recognition sequence, 5′-GCATC-3′ were cloned and sequenced. The Bst19I RM system includes two MTases, M1.Bst19I and M2.Bst19I. The SfaNI RM system has only one MTase, M.SfaNI, whose N and C domains are homologous to M2.Bst19I and M1.Bst19I, respectively. Both M1.Bst19I and M2.Bst19I and the two domains of M.SfaNI contain conserved elements, which are arranged in the order characteristic of class α N6-adenine MTases. The enzymes of the SfaNI and Bst19I RM systems proved to be highly homologous to their FokI and BstF5I counterparts, which was explained by the presence of the common tetranucleotide 5′-GATG-3′ in their recognition sites. Based on sequence homology, the spatial arrangement of highly conserved amino acid residues was determined using the known three-dimensional model of M.DpnIIA, which belongs to the same MTase class. |
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