Fission yeast Swi2 designates cell-type specific donor and stimulates Rad51-driven strand exchange

Abstract

AbstractA haploid of the fission yeastSchizosaccharomyces pombeexpresses either the P or M matingtype, determined by the active, euchromatic,mat1cassette. Mating-type is switched by Rad51-driven gene conversion ofmat1using a heterochromatic donor cassette,mat2-Pormat3-M. The Swi2-Swi5 complex, a mating-type switching factor, is central to this process by designating a preferred donor in a cell-type-specific manner. Swi2-Swi5 selectively enables one of twocisacting recombination enhancers,SRE2adjacent tomat2-PorSRE3adjacent tomat3-M. Here, we identified two functionally important motifs in Swi2, a Swi6 (HP1 homolog)-binding site and two DNA-binding AT-hooks. Genetic analysis demonstrated that the AT-hooks were required for Swi2 localization atSRE3to select themat3-Mdonor in P cells, while the Swi6-binding site was required for Swi2 localization atSRE2to selectmat2-Pin M cells. In addition, the Swi2-Swi5 complex promoted Rad51-driven strand exchangein vitro. Taken together, our results show how the Swi2-Swi5 complex would localize to recombination enhancers through a cell-type specific binding mechanism and stimulate Rad51-driven gene conversion at the localization site.