Originally published as Genetics Published Articles Ahead of Print on July 29, 2007.

Genetics, Vol. 177, 255-265, September 2007, Copyright © 2007
doi:10.1534/genetics.107.076315

Schizosaccharomyces pombe Switches Mating Type by the Synthesis-Dependent Strand-Annealing Mechanism

* Marie Curie Research Institute, Surry RH8 0TL, United Kingdom and {dagger} Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 21702-1201

1 Corresponding author: DNA Replication Laboratory, Marie Curie Research Institute, The Chart, Oxted, Surrey RH8 0TL, United Kingdom.
E-mail: j.dalgaard{at}mcri.ac.uk

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 provide an in vivo genetic test of the proposed molecular recombination mechanism.




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