Abstract
The UV mixing titration, gel electrophoresis, and CD measurements indicate that oligomers with a basic sequence of 5′-d-T-(C-T-)2C-(T-)4C-(T-C-)2T form a hairpin type triplex with the target 5′-d-A-(G-A-)2G. The stability, measured UV melting temperatures, were studied in aqueous solution as functions of mC (5-methylcytidine) replacement of C, pH (4 to 7), and salt concentration (up to 1 M). The order of stability is 5′-d-A-(G-A-)-2G + 5′-d-T-(C-T-)2C-(T-)4C- (T-C-)2T < 5′-d-A-(G-A-)2G + 5′-d-T-(mC-T-)2 mC-(T-)4C-(T-C-)2T ≈ 5′-d-A-(G-A-)2G + 5′-d-T-(C-T-)2C-(T-)4 mC-(T-mC-)2T < 5′-d-A-(G-A-)2G + 5′-d-T-(mC-T-)2 mC-(T-)4 mC-(T-mC-)2T at pH 4. These results indicate that (a) a stable triplex is formed with three T · A · T and three C+ · G · C base triads and (b) mC is more effective than C to stablize the triplex formation in acidic condition. Thus, this provides a simple system for further studies of triplex.