MOLECULAR ANALYSIS OF THE DHP1(+) GENE OF SCHIROSACCHAROMYCES POMBE - AN ESSENTIAL GENE THAT HAS HOMOLOGY TO THE DST2 AND RAT1 GENES OF SACCHAROMYCES-CEREVISIAE

The DST2 gene of Saccharomyces cerevisiae encodes a DNA strand exchange protein, STP beta, which is required for homologous recombination in both mitotic or meiotic cells. We have cloned a DST2-related gene from the fission yeast Schizosaccharomyces pombe and designated it dhp1(+). The nucleotide sequence of dhp1(+) revealed an open reading frame encoding a protein composed of 991 amino acids. The predicted amino acid sequence was significantly homologous to the S. cerevisine STP beta, but lacked the carboxy-terminal sequence present in STP beta. Furthermore, dhp1(+) shows greater homology to RAT1/HKE1, a gene which is involved in RNA trafficking and processing. Genetic experiments showed that dhp1(+) on an S. cerevisiae expression vector could rescue both the defects of the S. cerevisiae DST2 disruptant, slow growth rate and a sporulation defect, and the lethality of the S. cerevisiae rat1(ts) mutation. This implies the functional similarity of dhp1(+) to both DST2 and RAT1. However unlike DST2, dhp1(+) is an essential gene for cell growth in S. pombe, suggesting that dhp1(+) is not the true homologue of DST2 but rather of RAT1 in S. pombe. The possible roles of dhp1(+) in recombination and cell growth in S. pombe are discussed.