title: Epigenetic inheritance of transcriptional silencing and switching competence in fission yeast.
abstract: Epigenetic events allow the inheritance of phenotypic changes that are not caused by an alteration in DNA sequence. Here we characterize an epigenetic phenomenon occurring in the mating-type region of fission yeast. Cells of fission yeast switch between the P and M mating-type by interconverting their expressed mating-type cassette between two allelic forms, mat1-P and mat1-M. The switch results from gene conversions of mat1 by two silent cassettes, mat2-P and mat3-M, which are linked to each other and to mat1. GREWAL and KLAR observed that the ability to both switch mat1 and repress transcription near mat2-P and mat3-M was maintained epigenetically in a strain with an 8-kb deletion between mat2 and mat3. Using a strain very similar to theirs, we determined that interconversions between the switching- and silencing-proficient state and the switching and silencing-deficient state occurred less frequently than once per 1000 cell divisions. Although transcriptional silencing was alleviated by the 8-kb deletion, it was not abolished. We performed a mutant search and obtained a class of trans-acting mutations that displayed a strong cumulative effect with the 8-kb deletion. These mutations allow to assess the extent to which silencing is affected by the deletion and provide new insights on the redundancy of the silencing mechanism.
authors.affiliation: Department of Genetics, Institute of Molecular Biology, University of Copenhagen, Denmark. gen@biobase.dk
authors.forename: G
authors.initials: G
authors.lastname: Thon
authors.forename: T
authors.initials: T
authors.lastname: Friis
mesh_terms: D000483:Alleles; D017353:Gene Deletion; D015321:Gene Rearrangement; D005800:Genes, Fungal; D049770:Genes, Mating Type, Fungal; D008938:Mitosis / Q000235:genetics; D009154:Mutation; D010641:Phenotype; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics*; D014158:Transcription, Genetic