Conserved and Nonconserved Proteins for Meiotic DNA Breakage and Repair in Yeasts

Abstract

During meiosis DNA double-strand breaks initiate recombination in the distantly related budding and fission yeasts and perhaps in most eukaryotes. Repair of broken meiotic DNA is essential for formation of viable gametes. We report here distinct but overlapping sets of proteins in these yeasts required for formation and repair of double-strand breaks. Meiotic DNA breakage in Schizosaccharomyces pombe did not require Rad50 or Rad32, although the homologs Rad50 and Mre11 are required in Saccharomyces cerevisiae ; these proteins are required for meiotic DNA break repair in both yeasts. DNA breakage required the S. pombe midmeiosis transcription factor Mei4, but the structurally unrelated midmeiosis transcription factor Ndt80 is not required for breakage in S. cerevisiae. Rhp51, Swi5, and Rad22 ϩ Rti1 were required for full levels of DNA repair in S. pombe, as are the related S. cerevisiae proteins Rad51, Sae3, and Rad52. Dmc1 was not required for repair in S. pombe, but its homolog Dmc1 is required in the well-studied strain SK1 of S. cerevisiae. Additional proteins required in one yeast have no obvious homologs in the other yeast. The occurrence of conserved and nonconserved proteins indicates potential diversity in the mechanism of meiotic recombination and divergence of the machinery during the evolution of eukaryotes. I N most eukaryotes homologous recombination ocobserved more recently in a second organism, the distantly related fission yeast Schizosaccharomyces pombe (Cercurs at high levels during meiosis to aid the proper segregation of homologs at the first meiotic division vantes et al. 2000). There are two lines of indirect evidence for meiotic ds breaks in other organisms. First, and to increase genetic diversity among gametes, the products of meiosis. The two meiotic cell divisions revarious eukaryotes encode homologs of the Spo11 protein, which is essential for meiotic DNA ds break formaduce the diploid number of chromosomes in the precursor cells to the haploid number in the gametes. The tion in S. cerevisiae (Keeney et al. 1997). Where tested in other organisms, these proteins are essential for meiotic general mechanism of reductional segregation of homologs is highly conserved: in most eukaryotes recombinarecombination or viable gamete formation (Keeney 2001), and in S. pombe the homolog, called Rec12, is tion between homologs provides a physical connection between them that imparts tension when the homologs also essential for meiotic DNA ds break formation (Cervantes et al. 2000). Second, in mice a modified histone, are properly arranged to segregate to opposite poles of the cell (Nicklas 1997). In the absence of recombina-␥-H2AX, thought to associate with chromatin specifically near ds breaks, appears as foci on meiotic chromotion, homologs frequently missegregate, resulting in aneuploid gametes; the subsequent zygotic progeny are somes at the time expected for recombination; these foci are Spo11 dependent (Rogakou et al. 1998; Mahafrequently sick or dead, underscoring the importance of un...

Mei4p coordinates the onset of meiosis I by regulating cdc25 + in fission yeast

“…Although Mei4p is thought to be an important regulator of middle gene expression during meiosis, with many Mei4p target genes thought to be indispensable for progression through meiotic nuclear division, the precise contribution of Mei4p to meiotic nuclear division has remained unknown. We showed (20), however, that Cdc2p is phosphorylated on Tyr 15 in mei4 mutant cells. We now show that phosphorylation of Cdc2p on Tyr 15 is responsible for the arrest of mei4 mutant cells, given that forced dephosphorylation of this residue induced meiotic nuclear division without a delay.…”

“…Phosphorylation of Cdc2p on Tyr 15 Is Responsible for the Arrest of mei4 Mutant Cells. To facilitate the synchronous induction of meiosis, we studied a temperature-sensitive pat1 strain of Schizosaccharomyces pombe.…”

“…Among the potential Mei4p target genes, spo6 ϩ is required for sporulation (11). mde2 ϩ has been identified as a Mei4p target gene, and its product is required for formation of DNA double-strand breaks (13,14), a process that is essential for meiotic recombination, consistent with the fact that Mei4p is also required for double-strand break formation (15).…”

“…The activity of Cdc2p is determined by the phosphorylation status of its Tyr 15 residue and the availability of cyclin (16,17). Inhibitory phosphorylation of Cdc2p on Tyr 15 is catalyzed by the tyrosine kinases Wee1p and Mik1p, and the dephosphorylation of this residue is mediated predominantly by the tyrosine phosphatase Cdc25p (16,17).…”

Interactions between Mei4, Rec114, and other proteins required for meiotic DNA double-strand break formation in Saccharomyces cerevisiae

“…S1c). Modest sequence similarity has been described between Rec114 and Rec7 Molnar et al 2001), a protein required for initiation of meiotic recombination in Schizosaccharomyces pombe (Davis and Smith 2001;Young et al 2004;Lorenz et al 2006). The main region of similarity centers on the sequence RFQ (residues 109-111 in Rec114 and 93-95 in Rec7).…”