NDT80 and the Meiotic Recombination Checkpoint Regulate Expression of Middle Sporulation-Specific Genes in Saccharomyces cerevisiae

ABSTRACT

Distinct classes of sporulation-specific genes are sequentially expressed during the process of spore formation in Saccharomyces cerevisiae. The transition from expression of early meiotic genes to expression of middle sporulation-specific genes occurs at about the time that cells exit from pachytene and form the meiosis I spindle. To identify genes encoding potential regulators of middle sporulation-specific gene expression, we screened for mutants that expressed early meiotic genes but failed to express middle sporulation-specific genes. We identified mutant alleles ofRPD3, SIN3, and NDT80 in this screen. Rpd3p, a histone deacetylase, and Sin3p are global modulators of gene expression. Ndt80p promotes entry into the meiotic divisions. We found that entry into the meiotic divisions was not required for activation of middle sporulation genes; these genes were efficiently expressed in a clb1 clb3 clb4 strain, which fails to enter the meiotic divisions due to reduced Clb-dependent activation of Cdc28p kinase. In contrast, middle sporulation genes were not expressed in a dmc1 strain, which fails to enter the meiotic divisions because a defect in meiotic recombination leads to aRAD17-dependent checkpoint arrest. Expression of middle sporulation genes, as well as entry into the meiotic divisions, was restored to a dmc1 strain by mutation of RAD17. Our studies also revealed that NDT80 was a temporally distinct, pre-middle sporulation gene and that its expression was reduced, but not abolished, on mutation of DMC1,RPD3, SIN3, or NDT80 itself. In summary, our data indicate that Ndt80p is required for expression of middle sporulation genes and that the activity of Ndt80p is controlled by the meiotic recombination checkpoint. Thus, middle genes are expressed only on completion of meiotic recombination and subsequent generation of an active form of Ndt80p.

ACKNOWLEDGMENTS

We express our appreciation to Shelley Chu and Ira Herskowitz for communicating prior to publication their observation that Ndt80p is an autoregulatory transcriptional activator that binds to MSE elements, and we thank Ira Herskowitz for comments on this manuscript. We thank members of the labs of Brenda Andrews, Doug Bishop, Shelly Esposito, Bruce Futcher, Richard Gaber, Craig Giroux, Nancy Kleckner, Aaron Mitchell, Mike Tyers, Andrew Vershon, and Ted Weinert for providing plasmids and strains; Cheryl Smith of the Flow Cytometry Facility of the Department of Immunology, University of Toronto, for assistance with FACS analysis; and Saul Honigberg, Doug Bishop, and Craig Giroux for helpful discussions. We are very grateful to Chloe Cunningham and Aldo Mistretta for their help in patching cells.

S.R.H. was supported in part by a studentship from the National Sciences and Engineering Research Council (Canada). This work was supported by a Medical Research Council (Canada) grant (MA-6826) to J.S.