Originally published as Genetics Published Articles Ahead of Print on August 22, 2005.

Genetics, Vol. 171, 1499-1511, December 2005, Copyright © 2005
doi:10.1534/genetics.105.046821

Activation of an Alternative, Rec12 (Spo11)-Independent Pathway of Fission Yeast Meiotic Recombination in the Absence of a DNA Flap Endonuclease

Joseph A. Farah, Gareth Cromie, Luther Davis, Walter W. Steiner1 and Gerald R. Smith2

Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024

2 Corresponding author: Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. North, A1-162, Seattle WA, 98109-1024.
E-mail: gsmith{at}fhcrc.org

Spo11 or a homologous protein appears to be essential for meiotic DNA double-strand break (DSB) formation and recombination in all organisms tested. We report here the first example of an alternative, mutationally activated pathway for meiotic recombination in the absence of Rec12, the Spo11 homolog of Schizosaccharomyces pombe. Rad2, a FEN-1 flap endonuclease homolog, is involved in processing Okazaki fragments. In its absence, meiotic recombination and proper segregation of chromosomes were restored in rec12{Delta} mutants to nearly wild-type levels. Although readily detectable in wild-type strains, meiosis-specific DSBs were undetectable in recombination-proficient rad2{Delta} rec12{Delta} strains. On the basis of the biochemical properties of Rad2, we propose that meiotic recombination by this alternative (Rec*) pathway can be initiated by non-DSB lesions, such as nicks and gaps, which accumulate during premeiotic DNA replication in the absence of Okazaki fragment processing. We compare the Rec* pathway to alternative pathways of homologous recombination in other organisms.