[DNA-methylase Sau 3A: isolation and various properties].

DNA-methylase Sau 3A has been isolated for the first time from Staphylococcus aureus 3A cells and purified by column chromatography on phosphocellulose PII, heparin-Sepharose and blue Sepharose. The purified enzyme methylates the GATC sequence with the formation of GATm5C as can be evidenced from the protection of DNA from digestion with restrictases Sau 3A and Bam HI, the lack of the C3H3-group incorporation into Sau 3A DNA-restricts and the formation of a single methylated base m5C. Sau 3A methylase modifies only a two-filament (but not one-filament) DNA. Thus, methylase Sau 3A modifies the both DNA chains in the recognition site during a single binding act. The 5-azacytidine-containing DNA inhibits by 95% the activity of methylase Sau 3A. Ado-met is the single methyl group donor for methylase Sau 3A. The presence of m6A in the recognition site does not affect the activity of methylase Sau 3A. The practical recommendations for the use of M. Sau 3A, alongside with M. Eco dam, for the study of dam methylation by additional methylation of the DNA in vitro in the presence of [methyl-3H]-S-adenosyl-methionine are given.