The Fission Yeast dis3⁺ Gene Encodes a 110-kDa Essential Protein Implicated in Mitotic Control

Abstract

The fission yeast mutant dis3-54 is defective in mitosis and fails in chromosome disjunction. Its phenotype is similar to that of dis2-11, a mutant with a mutation in the type 1 protein phosphatase gene. We cloned the dis3⁺ gene by transformation. Nucleotide sequencing predicts a coding region of 970 amino acids interrupted by a 164-bp intron at the 65th codon. The predicted dis3⁺ protein shares a weak but significant similarity with the budding yeast SSD1 or SRK1 gene product, the gene for which is a suppressor for the absence of a protein phosphatase SIT4 gene or the BCY1 regulatory subunit of cyclic AMP-dependent protein kinase. Anti-dis3 antibodies recognized the 110-kDa dis3⁺ gene product, which is part of a 250- to 350-kDa oligomer and is enriched in the nucleus. The cellular localization of the dis3⁺ protein is reminiscent of that of the dis2⁺ protein, but these two proteins do not form a complex. A type 1 protein phosphatase activity in the dis3-54 mutant extracts is apparently not affected. The dis3⁺ gene is essential for growth; gene disruptant cells do not germinate and fail in cell division. Increased dis3⁺ gene dosage reverses the Ts⁺ phenotype of a cdc25 wee1 strain, as does increased type 1 protein phosphatase gene dosage. Double mutant dis3 dis2 is lethal even at the permissive temperature, suggesting that the dis2⁺ and dis3⁺ genes may be functionally overlapped. The role of the dis3⁺ gene product in mitosis is unknown, but this gene product may be directly or indirectly involved in the regulation of mitosis.