Published online 18 August 2004
Nucleic Acids Research, Vol. 32 No. 15 © Oxford University Press 2004; all rights reserved
A novel type of silencing factor, Clr2, is necessary for transcriptional silencing at various chromosomal locations in the fission yeast Schizosaccharomyces pombe
1 Department of Biosciences, Karolinska Institutet and Department of Natural Sciences, Sodertorn University College, 141 89 Huddinge, Sweden and 2 Department of Genetics, Institute of Molecular Biology, University of Copenhagen, DK-1353 Copenhagen K, Denmark
* To whom correspondence should be addressed at present address: Department of Medical Biochemistry and Microbiology, University of Uppsala, Box 582,SE-751 23 Uppsala, Sweden. Tel: +46 18 471 6652; Fax: +46 18 471 4673; Email: Pernilla.Bjerling{at}imbim.uu.se
Received April 20, 2004; Revised July 23, 2004; Accepted August 2, 2004
The mating-type region of the fission yeast Schizosaccharomyces pombe comprises three loci: mat1, mat2-P and mat3-M. mat1 is expressed and determines the mating type of the cell. mat2-P and mat3-M are two storage cassettes located in a 17 kb heterochromatic region with features identical to those of mammalian heterochromatin. Mutations in the swi6+, clr1+, clr2+, clr3+, clr4+ and clr6+ genes were obtained in screens for factors necessary for silencing the mat2-P–mat3-M region. swi6+ encodes a chromodomain protein, clr3+ and clr6+ histone deacetylases, and clr4+ a histone methyltransferase. Here, we describe the cloning and characterization of clr2+. The clr2+ gene encodes a 62 kDa protein with no obvious sequence homologs. Deletion of clr2+ not only affects transcriptional repression in the mating-type region, but also centromeric silencing and silencing of a PolII-transcribed gene inserted in the rDNA repeats. Using chromatin immunoprecipitation, we show that Clr2 is necessary for histone hypoacetylation in the mating-type region, suggesting that Clr2 acts upstream of histone deacetylases to promote transcriptional silencing.