[Show abstract][Hide abstract] ABSTRACT: Meiosis divides the chromosome number of the cell in half by having two rounds of chromosome segregation follow a single round of chromosome duplication. The first meiotic division is unique in that homologous pairs of sister chromatids segregate to opposite poles. Recent work in budding and fission yeast has shown that the cell cycle kinase, Cdc7-Dbf4, is required for many meiosis-specific chromosomal functions necessary for proper disjunction at meiosis I. This work reveals another role for Cdc7 in meiosis as a gene-specific regulator of the global transcription factor, Ndt80, which is required for exit from pachytene and entry into the meiotic divisions in budding yeast. Cdc7-Dbf4 promotes NDT80 transcription by relieving repression mediated by a complex of Sum1, Rfm1, and a histone deacetylase, Hst1. Sum1 exhibits meiosis-specific Cdc7-dependent phosphorylation, and mass spectrometry analysis reveals a dynamic and complex pattern of phosphorylation events, including four constitutive cyclin-dependent kinase (Cdk1) sites and 11 meiosis-specific Cdc7-Dbf4-dependent sites. Analysis of various phosphorylation site mutants suggests that Cdc7 functions with both Cdk1 and the meiosis-specific kinase Ime2 to control this critical transition point during meiosis.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have shown that the meiosis-specific kinase, Mek1, plays a key role in promoting recombination between homologous chromosomes during meiosis in budding yeast by suppressing recombination between sister chromatids, as well as playing a role in the meiotic recombination checkpoint. Understanding how Mek1 regulates recombination requires the identification of direct substrates of the kinase. We have applied the semi-synthetic epitope method developed by Shokat and colleagues to Mek1. This method uses an analog-sensitive version of Mek1, GST-Mek1-as, in conjunction with an ATPγS analog, for kinase assays that detect only those proteins that are directly phosphorylated by Mek1. This method may be applicable to any kinase for which an analog-sensitive version is available. In addition, it provides a non-radioactive alternative for kinase assays with wild-type kinases.
[Show abstract][Hide abstract] ABSTRACT: In budding yeast, as in other eukaryotes, the Cdc7 protein kinase is important for initiation of DNA synthesis in vegetative cells. In addition, Cdc7 has crucial meiotic functions: it facilitates premeiotic DNA replication, and it is essential for the initiation of recombination. This work uses a chemical genetic approach to demonstrate that Cdc7 kinase has additional roles in meiosis. First, Cdc7 allows expression of NDT80, a meiosis-specific transcriptional activator required for the induction of genes involved in exit from pachytene, meiotic progression, and spore formation. Second, Cdc7 is necessary for recruitment of monopolin to sister kinetochores, and it is necessary for the reductional segregation occurring at meiosis I. The use of the same kinase to regulate several distinct meiosis-specific processes may be important for the coordination of these processes during meiosis.
Molecular biology of the cell 10/2008; 19(11):4956-67. DOI:10.1091/mbc.E08-07-0755 · 4.47 Impact Factor