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 of RPD3, 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 Clbdependent 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 a RAD17-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.Sporulation is a process of cellular differentiation that is initiated in diploid a/␣ cells of the yeast Saccharomyces cerevisiae in response to nitrogen starvation in the presence of a nonfermentable carbon source. As a cell progresses through the events of meiosis and spore wall formation, a coordinated series of genetic and morphological events generates a tetrad of haploid spores within an ascus (reviewed in references 9 and 30). The sporulation program begins when starved cells exit the mitotic cell cycle and undergo premeiotic DNA replication. This is followed by a lengthy prophase in which homologous chromosomes pair, the synaptonemal complex (SC) is elaborated, and a high level of genetic recombination occurs. At pachytene, the penultimate stage of prophase and the last stage at which cells can return to mitotic growth, the chromosomes are fully synapsed, and the spindle pole bodies lie sideby-side in the nuclear envelope. As cells exit from pachytene, the SC disassembles, chiasmata appear, and the spindle pole bodies separate to form the meiosis I spindle. The two meiotic divisions occur in rapid succession, leading first to segregation of homologous chromosome...

Genomewide studies of histone deacetylase function in yeast

“…Some of these up-regulated genes previously have been described as repressed by SIN3, RPD3, or both ( Fig. 1C) (18)(19)(20). Although genes reported to be regulated by RPD3 and SIN3 were similarly affected in the profiles, the vast majority of up-regulated transcripts have not been described previously.…”

Glucose-mediated Phosphorylation Converts the Transcription Factor Rgt1 from a Repressor to an Activator

“…2 Experiments are under way to test whether the observed changes in histone acetylation at the HXT gene promoters are mediated by Rgt1. In addition, being an activator itself, Ume6 also induces the expression of another transcription factor, Ndt80, that activates middle genes (25). Similar to Ume6, Rgt1 is also likely to stimulate the expression of a transcriptional activator that is required for maximal expression of the HXT1 gene in response to high concentrations of glucose (Fig.…”

Arg-Pro-X-Ser/Thr Is a Consensus Phosphoacceptor Sequence for the Meiosis-Specific Ime2 Protein Kinase in Saccharomyces cerevisiae

“…MSGs contain a DNA sequence, the middle sporulation element (MSE), in their promoter regions (16). The MSE is targeted by the transcriptional activator Ndt80, which itself is expressed specifically in meiosis just prior to induction of most MSGs (4,9). Ndt80 is phosphorylated by Ime2 in vitro, and yeast lacking Ime2 accumulate a hypophosphorylated form of Ndt80 (1,27,28).…”