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 t here is no direct evidence for triplexes in vivo, cellular proteins that, s pecifically recognize tripler DNA have been described. Using a purine-motif tripler probe and southwestern library screening, we isolated five indepen dent clones expressing the same C-terminal 210 amino acids of the Saccharom yces cerevisiae protein Cdp1p fused with beta -galactosidase. In electropho retic mobility shift assays, recombinant Cdp1p Delta1-867 bound Pu-motif tr ipler DNAs with high affinity (K-d similar to5 nM) and bound Py-motif tripl er, 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 prope r chromosome segregation. The possible involvement of tripler DNA in this p rocess is discussed.