A new type of mutation in Schizosaccharomyces pombe: vegetative iodine reaction.

Colonies of Schizosaccharomyces pombe that contain ascospores (e.g., colonies of homothallic strains) turn black after treatment with iodine vapors. Heterothallic strains of S. pombe normally do not show this reaction. In experiments with the latter strains we found mutants which exhibit a positive iodine reaction though they do not contain ascospores. This phenotype is due to mutations in a new gene, vir1 (vegatative iodine reaction). The vir1 locus is not linked with the mating-type genes.--Strains of mating-type h-S are known not to give any spontaneous mating-type mutations. Mating-type mutations were also not found after treatment with nitrous acid.