The protein Cdc13p binds telomeres in vivo and is essential for the maintenance of the telomeres of Saccharomyces cerevisiae. In addition, Cdc13p is known to bind single-stranded TG1-3 DNA in vitro. Here we have shown that Cdc13p also binds DNA quadruplex, G-quartet, formed by TG 1-3 DNA. Moreover, the binding of Cde13p causes a partial denaturing of the G-quartet DNA. Formation of DNA quadruplexes may involve the intermolecular association of TG1-3 DNA and inhibit the extension of telomeres by telomerase. Thus, our finding suggests that Cde13p may disrupt telomere association and facilitate telomere replication.
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