Orientation of “plus” genes at the mating-type locus in homothallic fission yeast

Abstract

Results of four crosses are presented, which indicate that, in Schizosaccharomyces pombe, the plus segment of the mating-type locus is regulated from a central position, in between of the plus and the minus segment. This conclusion is based on the mapping of a plus-restraining entity r, which is revealed by recombination in certain crosses, or by mutation to unstable ⊖ strains. To this end, a meiosis-defective mating-type mutation was used as a marker for the plus segment, by taking advantage of its suppressibility by a nonsense suppressor. This suppressibility was substantiated by an additional cross.