Interaction of Yeast Repressor-Activator Protein Ume6p with Glycogen Synthase Kinase 3 Homolog Rim11p

Abstract

Meiosis and expression of early meiotic genes in the budding yeast Saccharomyces cerevisiae depend upon Rim11p, Ume6p, and Ime1p. Rim11p (also called Mds1p and ScGSK3) is a protein kinase related to glycogen synthase kinase 3 (GSK3); Ume6p is an architectural transcription factor; and Ime1p is a Ume6p-binding protein that provides a transcriptional activation domain. Rim11p is required for Ime1p-Ume6p interaction, and prior studies have shown that Rim11p binds to and phosphorylates Ime1p. We show here that Rim11p binds to and phosphorylates Ume6p, as well. Amino acid substitutions in Ume6p that alter a consensus GSK3 site reduce or abolish Rim11p-Ume6p interaction and Rim11p-dependent phosphorylation, and they cause defects in interaction between Ume6p and Ime1p and in meiotic gene expression. Therefore, interaction between Rim11p and Ume6p, resulting in phosphorylation of Ume6p, is required for Ime1p-Ume6p complex formation. Rim11p, like metazoan GSK3␤, phosphorylates both interacting subunits of a target protein complex.Meiosis and spore formation of the budding yeast Saccharomyces cerevisiae are initiated by one type of cell, the a/␣ cell, when growth is blocked by nitrogen starvation in the absence of glucose (8). Initiation of meiosis is coupled to activation of a set of early meiotic genes whose products participate in meiotic prophase and division (reviewed in references 11 and 30). The protein kinase Rim11p is required for early meiotic gene expression. Rim11p is a homolog of vertebrate glycogen synthase kinase 3 (GSK3) and of Drosophila Shaggy (2, 4, 28). Members of this protein kinase subfamily have diverse roles in cellular differentiation and transcriptional regulation (reviewed in references 13, 25, and 45). We report here an analysis of the mechanism by which Rim11p activates yeast meiotic genes.Early meiotic gene expression is governed by the DNAbinding protein Ume6p. Ume6p has a C-terminal DNA-binding domain (39), a central repression domain (16), and an N-terminal region required for transcriptional activation (5). In nonmeiotic cells (such as growing cells), Ume6p functions as a transcriptional repressor. Repression is exerted through association of Ume6p with Sin3p and the histone deacetylase Rpd3p (16). In meiotic cells, Ume6p functions as a transcriptional activator. Activation depends upon association of the Ume6p N-terminal domain with a second protein, Ime1p, which provides a transcriptional activation domain (20,32,36). Ime1p is expressed at its highest levels in early meiotic prophase, thus restricting activation by Ime1p-Ume6p to the time of meiotic initiation.Rim11p is required for activation by Ime1p-Ume6p (4, 22). Past studies have indicated that Rim11p stimulates meiotic genes through its interaction with Ime1p. Ime1p is present in Rim11p immune complexes and is phosphorylated by Rim11p in vitro (4). Ime1p-Rim11p interaction is also detectable by two-hybrid interaction cloning (32). The finding that Rim11p is required for Ime1p-Ume6p two-hybrid interaction has led to the idea that ...

Cdc7-Dbf4 RegulatesNDT80Transcription as Well as Reductional Segregation during Budding Yeast Meiosis

“…When cells are transferred to Spo medium, a combination of genetic and nutritional signals results in the expression of the Ime1 transcriptional activator (Vershon and Pierce 2000). Ime1 and Ume6 are phosphorylated by the kinase Rim11, and this phosphorylation promotes the formation and activity of a Ume6/Ime1 complex at URS1 (Rubin-Bejerano et al, 1996;Malathi et al, 1997).…”

Nps1/Sth1p, a component of an essential chromatin‐remodeling complex of Saccharomyces cerevisiae, is required for the maximal expression of early meiotic genes

“…Transcriptional activation by Ume6p requires Rim11p and Ime1p. These proteins form a complex in which Rim11p phosphorylates Ime1p and Ume6p in vitro (Bowdish et al 1994;Rubin-Bejerano et al 1996;Malathi et al 1997). Rim15p may accelerate the Ime1-Ume6p interaction in the absence of glucose (Vidan & Mitchell 1997).…”

PP2ACdc55is required for multiple events during meiosis I

“…While CDC28 AF suppressed the loss of expression of SPS4 and DIT4 in cdc55 cells, expression levels were much lower than wild-type cells, and induction occurred all at once at 24 h. These results suggest phosphorylation/dephosphorylation regulates the temporal expression of meiotic genes, through a Cdc55-Swe1-Cdc28 pathway. [88][89][90] cdc55 null cells are blocked in meiosis I prior to sister chromatid separation. Recent work has shown cells prematurely separate sister chromatids during meiosis in the absence of securin and Cdc55.…”

“…The Ime1-Ume6 interaction is regulated by the Rim11 and Rim15 kinases. 89 Thus, there is a well defined regulatory loop responsible for Ume6 regulation, which may be perturbed in cdc55 cells. This may explain why we observe an altered meiotic gene expression pattern.…”