Identification of Residues in Yeast Spo11p Critical for Meiotic DNA Double-Strand Break Formation

Abstract

Saccharomyces cerevisiae Spo11 protein (Spo11p) is thought to generate the DNA double-strand breaks (DSBs) that initiate homologous recombination during meiosis. Spo11p is related to a subunit of archaebacterial topoisomerase VI and appears to cleave DNA through a topoisomerase-like transesterase mechanism. In this work, we used the crystal structure of a fragment of topoisomerase VI to model the Spo11p structure and to identify amino acid residues in yeast Spo11p potentially involved in DSB catalysis and/or DNA binding. These residues were mutated to determine which are critical for Spo11p function in vivo. Mutation of Glu-233 or Asp-288, which lie in a conserved structural motif called the Toprim domain, abolished meiotic recombination. These Toprim domain residues have been implicated in binding a metal ion cofactor in topoisomerases and bacterial primases, supporting the idea that DNA cleavage by Spo11p is Mg²⁺ dependent. Mutations at an invariant arginine (Arg-131) within a second conserved structural motif known as the 5Y-CAP domain, as well as three other mutations (E235A, F260R, and D290A), caused marked changes in the DSB pattern at a recombination hotspot, suggesting that Spo11p contributes directly to the choice of DNA cleavage site. Finally, certain DSB-defective mutant alleles generated in this study conferred a semidominant negative phenotype but only when Spo11p activity was partially compromised by the presence of an epitope tag. These results are consistent with a multimeric structure for Spo11p in vivo but may also indicate that the amount of Spo11 protein is not a limiting factor for DSB formation in normal cells.

We thank Julie Pui Yuen for constructing many of the untagged SPO11 alleles and Jennifer Giordano for her help in characterizing the altered DSB cleavage patterns. We also thank Bernard de Massy and Paul-Christophe Varoutas for discussions and sharing information prior to publication and Jerry Hurwitz, Ken Marians, and Stewart Shuman for critical comments on the manuscript.

This work was supported in part by grants to S.K. from the NIH (GM58673) and from the New York City Council Speaker's Fund for Biomedical Research.