ИСТИНА

DNA mismatch repair system (MMR) implements correction of nucleotide misincorporation. MutS is a protein responsible for mismatch recognition in the initial steps of MMR. The other DNA molecules adopting non-B-form configuration, in addition to mismatched DNA, may serve as the potential binding substrates for MutS. This can be associated with the alternative roles assigned to the MMR system in various organisms, including connections with other DNA repair systems, homologous recombination and apoptosis. Guanine quadruplexes (G4) are four-stranded non-canonical DNA structures formed by guanine-rich sequences present in living cells, possessing regulatory function and contributing to genome instability. Interaction of G4-DNA with Escherichia coli (E. coli) MutS and human MutSα homolog was detected previously [1, 2]. Nevertheless, additional data is required to comprehend the authentic role and mechanism of this interaction. Employing fluorescence polarization and EMSA we investigated DNA binding properties of MutS from E. coli and Rhodobacter sphaeroides using 41 bp fluorophore-labelled DNA with G/T mismatch or T-bulge as ligands. In order to evaluate the affinity of MutS to different types of DNA molecules we performed a competition assay, where the labeled heteroduplex was substituted for G-quadruplexes, duplexes containing GT-rich loop and DNAs with or without G/T mismatch. The approach was applied for detection of G4 structures in 76-mer DNA fragments.