A transcriptional autoregulatory loop for KIN28–CCL1 and SRB10–SRB11, each encoding RNA polymerase II CTD kinase–cyclin pair, stimulates the meiotic development of S. cerevisiae

Abstract

Alkalization of the medium is associated with and required for the cellular development to meiosis and sporulation in the yeast Saccharomyces cerevisiae. To elucidate the molecular mechanisms for the signi®cance of external alkalization, we isolated mutants defective in division arrest at G 1 phase under an alkaline condition. The mutants obtained had recessive alleles of SRB10 encoding the cyclin (SRB11)-dependent protein kinase that phosphorylates the CTD domain of the largest subunit of RNA polymerase II and negatively regulates the transcriptional initiation of certain genes. A Dsrb11 deletion mutant showed the same cell cycle defect. When shifted to alkali, wild-type cells decreased transcript levels of G 1 -cyclin genes (CLN1 to CLN3) and KIN28±CCL1 (encoding another CTD kinase±cyclin pair which, in contrast, stimulates the promoter clearance and transcriptional elongation in most genes), resulting in the accumulation of G 1 cells and the hypophosphorylated form of RNA polymerase II and in an increase in cell size. However, under the same conditions, a Dsrb10 mutant was defective in these events, except the downregulation of CLN1 and CLN2. The Dsrb10 mutation also in¯uenced on the transcript levels of meiosis-inducing genes called IME1 and IME2: the mutation elevated the transcript level of IME1 but reduced that of IME2, resulting in partial defects in premeiotic DNA synthesis and meiosis. Overexpression of KIN28 and CCL1 in wild-type cells impaired the alkali-induced G 1 arrest and the rate of meiosis and elevated the transcript levels of SRB11 and IME1. These results indicate that a transcriptional autoregulatory loop for KIN28±CCL1 and SRB10±SRB11 is important for G 1 arrest and meiosis. We also found that environmental conditions for meiosis ®nely regulate the transcript levels of KIN28 and CCL1, such that nitrogen starvation ®rst elevates them but subsequent alkalization of medium decreases them.

Sub1 Globally Regulates RNA Polymerase II C-Terminal Domain Phosphorylation

“…We next asked whether the effects of SUB1 deletion on Srb10 might contribute to the effects we observed on Kin28. Previous studies have shown that TFIIH is negatively regulated by CDK8-containing Mediator complexes in human cells (4) and that Srb10 inhibits KIN28 transcription in meiotic yeast cells (51). Extending these results, we observed that deletion of SRB10 resulted in an increase in Kin28-HA levels and, as a consequence, an increase in Kin28 activity, as analyzed by in vitro kinase assays (Fig.…”

Krh1p and Krh2p act downstream of the Gpa2p Gα subunit to negatively regulate haploid invasive growth

“…The KRH1 gene was identified previously by a mutation that causes cells to continue to grow when incubated in alkaline sporulation medium (Ohkuni and Yamashita, 2000). This medium contains acetate as a carbon source and is limiting for nitrogen, a nutritional condition that induces sporulation in wild-type cells.…”

Signal pathway integration in the switch from the mitotic cell cycle to meiosis in yeast

“…Respiration leads to the production of CO2 and hence causes alkalization of the medium. This alkalization may contribute to meiotic initiation (Ohkuni and Yamashita, 2000). For example Rim101p is required both for adaptation to extracellular alkalization ) and for IME1 transcription (Su and Mitchell, 1993).…”

“…For example Rim101p is required both for adaptation to extracellular alkalization ) and for IME1 transcription (Su and Mitchell, 1993). In addition, alkalization of the medium may also activate the Srb10p-Srb11p cyclinkinase complex (also called Ume3p-Ume5p and Ssn3p-Ssn8p), and this activation is required for efficient induction of IME2 transcription and initiation of meiosis (Cooper and Strich, 2002;Ohkuni and Yamashita, 2000). Thus respiration may promote both IME1 and IME2 expression by causing alkalization of the medium.…”