In eukaryotes, protein kinase C (PKC) is implicated in the regulation of many important cellular processes, including proliferation and polarized growth. In budding yeast, a single PKC (Pkc1p) activates the Mpk1p MAP kinase pathway that is essential for cell-wall construction and bud emergence. However, little is known about its other functions. Now, Masaki Mizunuma and colleagues report that Pkc1p maintains polarized bud growth in an Mpk1p-independent manner (see ). The authors describe how yeast cells carrying pkc1-834, a novel mutant allele of PKC1, establish polarity normally but do not maintain polarized growth during cell budding. Maintenance of Ca2+-induced F-actin polarization is defective in these mutant yeast cells, and this phenotype is apparently caused by decreased expression of the G1 cyclin Cln2p. The authors propose that this novel Mpk1p-independent role for Pkc1p and its previously described Mpk1p-dependent role are important for the coordinated regulation of polar bud growth and the cell cycle.
