DNA-methyltransferase SsoII interaction with own promoter region binding site

The investigation of SsoII DNA-methyltransferase (M.SsoII) interaction with the intergenic region of SsoII restriction-modification system was carried out. Seven guanine residues protected by M.SsoII from methylation with dimethylsulfate and thus probably involved in enzyme-DNA recognition were identified. Six of them are located symmetrically within the 15 bp inverted repeat inside the SsoII promoter region. The crosslinking of SsoII methyltransferase with DNA duplexes containing 5-bromo-2′-deoxyuridine (br5dU) instead of thymidine was performed. The crosslinked products were obtained in all cases, thus proving that tested thymines were in proximity with enzyme. The ability to produce the crosslinked products in one case was 2–5-fold higher than in other ones. This allowed us to imply that thymine residue in this position of the inverted repeat could be in contact with M.SsoII. Based on the experimental data, two symmetrical 4 bp clusters (GGAC), which could be involved in the interaction with M.SsoII in the DNA-protein complex, were identified. The model of M.SsoII interaction with its own promoter region was proposed.