Genetics. Published Articles Ahead of Print: July 29, 2007, Copyright © 2007
doi:10.1534/genetics.107.076315


A more recent version of this article appeared on September 1, 2007.

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S.pombe switches mating-type by the synthesis dependent strand annealing mechanism

Tomoko Yamada-Inagawa 1, Amar J.S. Klar 2 and Jacob Z. Dalgaard 1*

1 Marie Curie Research Institute
2 National Cancer Institute

* To whom correspondence should be addressed. E-mail: j.dalgaard{at}mcri.ac.uk.

Submitted on May 24, 2007
Revised on June 23, 2007
Accepted on 10 July 2007


Abstract

Schizosaccharomyces pombe cells can switch between two mating-types, plus (P) and minus (M). The change in cell type occurs due to a replication-coupled recombination event that transfers genetic information from one of the silent donor loci, mat2P or mat3M, into the expressed mating-type determining mat1 locus. The mat1 locus can as a consequence contain DNA encoding either P or M information. A molecular mechanism, known as synthesis-dependent strand annealing, has been proposed for the underlying recombination event. A key feature of this model is that only one DNA strand of the donor locus provides the information that is copied into the mat1. Here we test the model by constructing strains that switch using two different mutant P-cassettes introduced at the donor loci, mat2 and mat3. We show that in such strains wild-type P-cassette DNA is efficiently generated at mat1 through heteroduplex DNA formation and repair. The present data provides the in vivo genetic test of the proposed molecular recombination mechanism.

Key Words: DNA replication, Heteroduplex DNA, Schizosaccharomyces pombe, mating-type switching, recombination