A STUDY OF TRIPLEX FORMATION OF 5'-D-T-(C-T-)(2)C-(T-)(4)C-(T-C-)(2)T WITH 5'-D-A-(G-A-)(2)G - A HAIRPIN TRIPLEX WITH 3 T-CENTER-DOT-A-CENTER-DOT-T AND 3 C+CENTER-DOT-G-CENTER-DOT-C BASES TRIADS

The UV mixing titration, gel electrophoresis, and CD measurements indicate that oligomers with a basic sequence of 5'-d-T-(C-T-)(2)C-(T-)(4)C-(T-C-)(2)T form a hairpin type triplex with the target 5'-d-A-(G-A-)(2)G. The stability, measured UV melting temperatures, were studied in aqueous solution as functions of C-m (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-)(2)G + 5'-d-T-(C-T-)(2)C-(T-)(4)C-(T-C-)(2)T < 5'-d-A-(G-A-)(2)G + 5'-d-T-(C-m-T-)(2)C-m-(T-)(4)C-(T-C-)(2)T approximate to 5'-d-A-(G-A-)(2)G + 5'-d-T-(C-T-)(2)C-(T-)(4)C-m-(T-C-m-)(2)T < 5'-d-A-(G-A-)(2)G + 5'-d-T-(C-m-T-)(2)C-m-(T-)(4)C-m-(T-C-m-)(2)T at pH 4. These results indicate that (a) a stable tripler is formed with three T . A . T and three C+. G . C base triads and (b) C-m is more effective than C to stablize the tripler formation in acidic condition. Thus, this provides a simple system for further studies of tripler.