A putative homologue of the human autoantigen Ku from Saccharomyces cerevisiae

We have identified and purified a new DNA binding protein, designated HDF (high affinity DNA-binding factor) from Saccharomyces cerevisiae. HDF binds in a sequence-independent manner to the ends of double-stranded DNA. The protein appears as a stable heterodimer of two polypeptides with molecular masses of 70 and 85 kDa. We have cloned and sequenced the 70-kDa subunit of the HDF protein. The amino acid sequence shows a weak but significant homology with the p70 subunit of the human Ku autoantigen, a protein that also binds to the ends of double-stranded DNA. Hdf- strains generated by one-step gene disruption show a temperature-sensitive phenotype for growth at 37 degrees C. Cells arrest growth at 37 degrees C and after several hours appear as enlarged single-budded cells with abnormally high DNA content indicating a defect in the regulation of DNA replication coupled with or causing a cell cycle arrest in G2 or mitosis.