A DNA binding motif of meiotic recombinase Rec12 (Spo11) defined by essential glycine-202, and persistence of Rec12 protein after completion of recombination

The Rec 12 (Spo 11) protein of the fission yeast Schizosaccharomyces pombe is a meiosis-specific ortholog of the catalytic subunit of type VI topoisomerases and is thought to catalyze double-strand DNA breaks that initiate recombination. We tested the hypothesis that the rec12/117 allele affects the choice of pathways by which recombination is resolved. DNA sequence analysis revealed a single missense mutation in the coding region (rec12-G202E). The corresponding glycine-202 residue of Rec12 protein is strictly conserved in proteins of the Rec12/ Spol1/Top6A family. It maps to the base of the DNA binding pocket in the crystal structure of the archaeal ortholog, Top6A. The rec12-G202E mutants lacked crossover and non-crossover recombination, demonstrating that rec12-G202E does not affect choice of resolution pathway. Like rec12-D15 null mutants, the rec12-G202E mutants suffered chromosome segregation errors in meiosis 1. The Rec12-G202E protein was as stable as wild-type Rec12, demonstrating that glycine-202 is essential for a biochemical activity of Reel 2 protein, rather than for its stability. These findings suggest that Reel 2 facilitates binding of the meiotic recombinase to its substrate, DNA. Interestingly, the bulk of Rec 12 protein persisted until the time of anaphase 1, and a portion of Rec12 protein persisted until the time of anaphase 11, after which it was undetectable. This suggests that Rec12 protein has additional meiotic functions after completion of recombination in prophase, as inferred previously from genetic studies.