Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Winter, Edward
Mailing Address: Biochemistry and Mol. Pharm., Thomas Jefferson University, 233 South 10th St., Philadelphia, PA 19107, USA
Email Address: winter@lac.jci.tju.edu
Phone & FAX numbers: (215) 503-4139 & (215) 923-9162

#034

The pachytene checkpoint in Saccharomyces cerevisiae requires the Sum1 transcriptional repressor.
Anne Lindgren (1), David Bungard (1), Michael Pierce (2), Jianxin Xie (2), Andrew Vershon (2), Edward Winter (1)
(1) Biochemistry and Mol. Pharm., Thomas Jefferson University, 233 South 10th St., Philadelphia, PA 19107, USA; (2) Waksman Institute, 190 Frelinghuysen Rd., Rutgers University, Piscataway, NJ 08854

The transcriptional program of sporulation involves the sequential induction of temporally distinct classes of genes. Genes induced when cells are exiting meiotic prophase and entering the chromosomal divisions (middle genes) are activated by the Ndt80 DNA binding protein that specifically recognizes a promoter element termed the MSE. A subset of middle genes are repressed in mitotic cells by the Sum1 DNA binding protein that also specifically recognizes the MSE (Xie et al. 1999, EMBO J. 18:6448-54). Failure to complete meiotic recombination as observed in a dmc1 mutant, blocks the nuclear divisions (the pachytene checkpoint). Here we show that this block requires Sum1 as dmc1 sum1 double mutants undergo both nuclear divisions. In a sum1 dmc1 diploid, Sum1-repressible genes are expressed constitutively throughout meiosis and middle gene induction does not occur. In contrast, middle genes are induced when the dmc1 arrest is relieved by deletion of the RAD17 cell cycle checkpoint gene. Although the dmc1 sum1 and the dmc1 rad17 double mutants complete both nuclear divisions, they fail to complete spore morphogenesis. In contrast, a dmc1 sum1 rad17 triply mutant strain undergoes meiosis and forms morphologically normal spores. The results suggest that when recombination is blocked, Sum1 and Rad17 arrest meiotic progression by different pathways. Both pathways are required to arrest the meiotic divisions; either pathway is sufficient to prevent spore morphogenesis.

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