Dynamic regulation of PHO85 G1 cyclins contributes to cell cycle-dependent morphogenesis in budding yeast.
Jason Moffat, Dongqing Huang, Brenda Andrews
Department of Medical Genetics, University of Toronto, 8 Taddle Creek
Rd, Toronto, on m5s1a8, Canada
Cyclin-dependent kinases (Cdks) are key regulators of the cell division
cycle. Cell cycle progression in budding yeast requires commitment to
START and initiation of the G1 transcriptional program in order for bud
growth, cell wall construction and DNA replication to occur. The G1
cyclins Pcl1, Pcl2 and Pcl9 are three of ten cyclins that activate the
multifunctional Pho85 Cdk, that is involved in aspects of metabolism,
cell cycle, cell polarity and gene expression. We uncovered several
genetic interactions linking PCL1 and PCL2 to cell wall
maintenance/regulation and polarized growth. PCL1 and PCL2 showed strong
genetic interactions with effectors of Cdc42 function and components of
the cell integrity MAPK pathway; Cdc42 is required for polarity
establishment and the cell integrity MAPK pathway is required during
periods of polarized growth. The phenotype in these multiple mutants
suggests that events in G1 and S that affect cell shape cannot be
corrected until the morphogenesis checkpoint in G2-phase. Excitingly,
Pcl1, Pcl2 and Pcl9 localized to sites of polarization and to the bud
neck. These data are consistent with a suggested role for the Pcls in
the cytoplasm. Our study represents the first observation that G1
cyclins can localize in a dynamic fashion to polarization sites within a
yeast cell. We suggest that Pcl1 and Pcl2 help to promote normal cell
morphology through Cdc42-related functions.
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