Roles of the RAM signaling network in cell cycle progression in Saccharomyces cerevisiae
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The Saccharomyces cerevisiae Hym1p, Mob2p, Tao3p, Cbk1p, Sog2p and Kic1p proteins are thought to function together in the RAM signaling network, which controls polarized growth, cell separation and cell integrity. Whether these proteins also function as a network to affect cell proliferation is not clear. Here we examined cells lacking or over-expressing RAM components, and evaluated the timing of initiation of DNA replication in each case. Our results suggest opposing roles of RAM proteins, where only Hym1p can promote the transition from the G1 to S phase of the cell cycle. We also uncovered additive growth defects in strains lacking several pair-wise combinations of RAM proteins, possibly arguing for multiple roles of RAM components in the overall control of cell proliferation. Finally, our findings suggest that Hym1p requires the Dcr2p phosphatase to promote the G1/S transition, but it does not require the G1 cyclin Cln3p or the RAS pathway. Taken together, our results point to a complex regulation of cell proliferation by RAM proteins, in a non-uniform manner that was not previously anticipated.
KeywordsHYM1 START MO25 RAM
We thank F. Cross for the Cln3-PrA strain. We especially want to thank C. Boone for very generously providing us with a large number of ram mutant strains. This work was supported by a grant from the National Institutes of Health (R01-GM062377) to M.P.
- Kaiser C, Michaelis S, Mitchell A (1994) Methods in yeast genetics. Cold Spring Harbor Laboratory Press, Cold Spring HarborGoogle Scholar
- Pringle JR, Hartwell LH (1981) The Saccharomyces cerevisiae cell cycle. In: Strathern JD, Jones EW, Broach JR (eds) The molecular biology of the yeast Saccharomyces. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, pp 97–142Google Scholar
- Weiss EL, Kurischko C, Zhang C, Shokat K, Drubin DG, Luca FC (2002) The Saccharomyces cerevisiae Mob2p-Cbk1p kinase complex promotes polarized growth and acts with the mitotic exit network to facilitate daughter cell-specific localization of Ace2p transcription factor. J Cell Biol 158:885–900CrossRefPubMedGoogle Scholar