Heterochromatin Regulates Cell Type-Specific Long-Range Chromatin Interactions Essential for Directed Recombination

Mating-type switching in Schizosaccharomyces pombe involves replacing genetic information at the expressed mat1 locus with sequences copied from one of two silent donor loci, mat2-P or mat3-M, located within a 20-kb heterochromatic domain. Donor selection is dictated by cell type: mat2 is the preferred donor in M cells, and mat3 is the preferred donor in P cells. Here we show that a recombination-promoting complex (RPC) containing Swi2 and Swi5 proteins exhibits cell type-specific localization pattern at the silent mating-type region and this differential localization modulates donor preference during mating-type switching. In P cells, RPC localization is restricted to a recombination enhancer located adjacent to mat3, but in M cells, RPC spreads in cis across the entire silent mating-type interval in a heterochromatin-dependent manner. Our analyses implicate heterochromatin in long-range regulatory interactions and suggest that heterochromatin imposes at the mating-type region structural organization that is important for the donor-choice mechanism.