HDF2, the second subunit of the Ku homologue from Saccharomyces cerevisiae

The high affinity DNA binding factor (HDF) protein of Saccharomyces cerevisiae is composed of two subunits and specifically binds ends of double-stranded DNA. The 70-kDa subunit, HDF1, shows significant homology with the 70-kDa subunit of the human Ku protein. Like the Ku protein, HDF1 has been shown to be involved in recombination and double stranded DNA break repair. We have purified and cloned HDF2, the second subunit of the HDF protein. The amino acid sequence of HDF2 shows a 45.6% homology with the 80-kDa subunit of the Ku protein. HDF1 by itself does not bind DNA, while HDF2 protein on its own seems to displays DNA binding activity. Targeted disruption of the HDF2 gene causes a temperature-sensitive phenotype for growth comparable to the phenotype of hdf1(-) strains. The human Ku protein cannot complement this temperature-sensitive phenotype. hdf2(-) strains are sensitive to bleomycin and methyl methanesulfonate, but this sensitivity is reduced in comparison with hdf1(-) strains.