The Saccharomyces cerevisiae GSK-3 beta homologs.

Yeast cells carry four homologs of GSK-3beta, RIM11, MCK1, MRK1 and YGK3. The significant homologs are RIM11 and MCK1 that presumably arose from a recent genome duplication followed by a rapid divergence. Accordingly, these homologs phosphorylate specific substrates. Rim11 is essential for entry into meiosis, whereas Mck1 is essential for growth at elevated and low temperatures. Both kinases transmit nutrient signals, but Mck1 transmits additional signals including stress signals such as, temperature, osmotic shock and Ca(2+). Consequently, Mck1 plays a role in multiple functions, including cell wall integrity, meiosis and centromere function. The other two homologs, MRK1 and YGK3 that belong to the RIM11 and MCK1 phylogenetic trees, respectively, show no distinct phenotype. These paralogs posses redundant roles, though less important, with Rim11 and Mck1 functions. This review summarizes the cellular roles of these kinases, their mode of regulation, and the signals that they transmit.