Characterization of a partially fertile ras1-like ste10-UGA nonsense mutant of fission yeast.

Mutants which carry a leaky UGA nonsense mutation in the fertility gene ste10 are characterized by a deformed cell morphology which resembles that described in the literature for sterile ras1- (ste5) and ral1 to ral4 mutant cells. Although frequent conjugation attempts are observed in combinations of two ste10 mutant strains of opposite heterothallic mating type, zygotes and asci are formed only rarely and the fertility of such crosses remains low (not more than 1% of the fertility of comparable crosses of two ste+ wild-type strains). The fertility is considerably increased, however, in combinations of the ste10 mutant with ste+ wild-type strains (up to 10% if the h- partner, and more than 30% if the h+ partner, carries the ste10 mutation.