The yeast CDP1 gene encodes a triple-helical DNA-binding protein

The formation of triple-helical DNA has been implicated in several cellular processes, including transcription, replication and recombination. While there is no direct evidence for triplexes in vivo, cellular proteins that, specifically recognize tripler DNA have been described. Using a purine-motif tripler probe and southwestern library screening, we isolated five independent clones expressing the same C-terminal 210 amino acids of the Saccharomyces cerevisiae protein Cdp1p fused with beta -galactosidase. In electrophoretic mobility shift assays, recombinant Cdp1p Delta1-867 bound Pu-motif tripler DNAs with high affinity (K-d similar to5 nM) and bound Py-motif tripler, duplex and single-stranded DNAs with far lower affinity (0.5-5.0 muM). Genetic analyses revealed that the CDP1 gene product was required for proper chromosome segregation. The possible involvement of tripler DNA in this process is discussed.