Position effect variegation at the mating-type locus of fission yeast: a cis-acting element inhibits covariegated expression of genes in the silent and expressed domains.
Schizosaccharomyces pombe switches its mating type by transposing a copy of unexpressed genes from the respective mat2 or mat3 cassettes to mat1. The donor cassettes are located in a silent domain that is separated from the expressed mat1 cassette by the L region. We monitored the expression of ade6 from sites in the L region and examined the relationship between the expression state at these sites and at sites within the silent domain. Results indicate that: (1) the silent domain extends into the L region, but repression is gradually alleviated with increasing distance from mat2, and overexpression of swi6 enhances PEV in the L region; (2) a transcriptionally active chromatin state, associated with reporter gene expression in the L region, spreads toward the silent domain; (3) a cis-acting element, located at the junction between the L region and mat2-P, ensures repression in the silent domain, regardless of the expression state in the L region; and (4) repression in mat1-P cells is less stringently controlled than in mat1-M cells. We discuss the functional organization of the mat region and genetic elements that ensure separation between repressed and derepressed domains.
Ayoub
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N
Department of Molecular Biology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel 91010, USA.
Goldshmidt
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I
Cohen
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A
D000225:Adenine / Q000378:metabolism; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics*; D049770:Genes, Mating Type, Fungal; D012045:Regulatory Sequences, Nucleic Acid; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000235:genetics*; D017384:Sequence Deletion; D014157:Transcription Factors / Q000235:genetics
D004271:DNA, Fungal; D005656:Fungal Proteins; C075111:SWI6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000225:Adenine