A homolog of male sex-determining factor SRY cooperates with a transposon-derived CENP-B protein to control sex-specific directed recombination

Abstract

Schizosaccharomyces pombe cells switch mating type by replacing genetic information at the expressed mat1 locus with sequences copied from mat2-P or mat3-M silent donor loci. The choice of donor locus is dictated by cell type, such that mat2 is the preferred donor in M cells and mat3 is the preferred donor in P cells. Donor choice involves a recombination-promoting complex (RPC) containing Swi2 and Swi5. In P cells, the RPC localizes to a specific DNA element located adjacent to mat3, but in M cells it spreads across the silent mating-type region, including mat2-P. This differential distribution of the RPC regulates nonrandom choice of donors. However, celltype-specific differences in RPC localization are not understood. Here we show that the mat1-M-encoded factor Mc, which shares structural and functional similarities with the male sex-determining factor SRY, is highly enriched at the swi2 and swi5 loci and promotes elevated levels of RPC components. Loss of Mc reduces Swi2 and Swi5 to levels comparable to those in P cells and disrupts RPC spreading across the mat2/3 region. Mc also localizes to loci expressed preferentially in M cells and to retrotransposon LTRs. We demonstrate that Mc localization at LTRs and at swi2 requires Abp1, a homolog of transposon-derived CENP-B protein and that loss of Abp1 impairs Swi2 protein expression and the donor choice mechanism. These results suggest that Mc modulates levels of recombination factors, which is important for mating-type donor selection and for the biased gene conversion observed during meiosis, where M cells serve as preferential donors of genetic information. (1) and mating-type switching in the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe (2-5). In these distantly related yeast species, cells alternate between two distinct mating-type alleles by copying genetic information from one of the two silent donor loci to the active mating-type locus via highly orchestrated recombination processes (6-8).The mating-type region of S. pombe contains three linked locimat1, mat2, and mat3-located on chromosome 2. In wild-type homothallic strains, designated h 90 , mat2 is located ∼17 kb centromere-distal to mat1, whereas mat3 is separated from mat2 by an 11-kb interval ( Fig. 1) (8, 9). The mating type of a haploid cell is determined by the presence of P or M information at mat1 (8). Each allele consists of two divergently transcribed genes (10). mat1-P contains the Pc and Pi genes, and mat1-M contains the Mc and Mi genes. mat2 and mat3 contain the same genetic information as mat1-P and mat1-M, respectively, but are maintained in a silent state. These silent mating-type cassettes are embedded in a 20-kb heterochromatin domain surrounded by inverted repeat (IR-R and IR-

CENP-B Cooperates with Set1 in Bidirectional Transcriptional Silencing and Genome Organization of Retrotransposons

“…The fission yeast CENP-Bs participate in several DNA-directed processes, including transcription, DNA replication, and recombination (1,9,35,37,72). Extensive occupancy of Abp1 and Cbh1 at diverse genetic elements throughout the fission yeast genome supports these multifaceted roles for CENP-Bs (9, 72).…”

“…CENP-Bbound LTRs could act as versatile regulatory modules, exerting transcriptional control of nearby genes (9,58) and affecting other DNA transactions, such as stabilizing DNA replication forks under certain genomic contexts (72). CENP-Bs also localize to non-LTR-associated promoters and regulate expression of associated genes, several of which are involved in sex-specific directed recombination (37). Most intriguingly, CENP-Bs contribute to the clustering of dispersed Tf2 elements into distinct Tf bodies (9) and thus play a role in genome organization.…”

Going in the Right Direction: Mating-Type Switching ofSchizosaccharomyces pombeIs Controlled by Judicious Expression of Two Differentswi2Transcripts

“…The Mc binding to this putative promoter might activate swi2S transcription. A recent chromatin immunoprecipitation analysis showed that Mc physically interacts with the swi2S promoter region, as predicted here (Matsuda et al 2011). Whether Mc binding depends on the two inverted presumptive recognition sites needs further investigation.…”

“…While we were preparing this manuscript for publication, it was reported (Matsuda et al 2011) that the Mc and Abp1 genes control the switching recombination directionality, that Mc protein directly binds to the Swi2 gene regulatory region, and that binding requires Abp1. Results of that report are complementary to some parts of our study and support our conclusions.…”

A Unique DNA Recombination Mechanism of the Mating/Cell-type Switching of Fission Yeasts: a Review

“…Swi2 binding to the mat region requires the SRE3, and it was proposed that in M cells Swi2 would reach to the mat2 region by spreading from the SRE3 through a heterochromatin region between mat2 and mat3 via physical interaction with Swi6 (54). Two more proteins, Abp1 and Mc, are required for Swi2 binding to the mat2 region, perhaps by promoting Swi2 spreading (56,57,58). The Mc protein, a transcription factor encoded within the M cassette, provides proper distribution of the RPC by positively regulating the expression of swi2 and swi5 genes in M cells (57).…”