Molecular analysis of the dhp1 + gene of Schizosaccharomyces pombe: an essential gene that has homology to the DST 2 and RAT 1 genes of Saccharomyces cerevisiae

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Abstract
The DST2 gene of Saccharomyces cerevisiae encodes a DNA strand exchange protein, STPβ, 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. cerevisiae STPβ, but lacked the carboxy-terminal sequence present in STPβ. 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.