Regulation of the actin cytoskeleton organization in yeast by a novel serine/threonine kinase Prk1p

Normal actin cytoskeleton organization in budding yeast requires the functi on of the Pan1p/End3p complex. Mutations in PAN1 and END3 cause defects in the organization of actin cytoskeleton and endocytosis. By screening for mu tations that can suppress the temperature sensitivity of a pan1 mutant (pan 1-4), a novel serine/threonine kinase Prk1p is now identified as a new fact or regulating the actin cytoskeleton organization in yeast. The suppression of pan1-4 by prk1 requires the presence of mutant Pan1p. Although viable, the prk1 mutant is unable to maintain an asymmetric distribution of the act in cytoskeleton at 37 degrees C. Consistent with its role in the regulation of actin cytoskeleton, Prk1p localizes to the regions of cell growth and c oincides with the polarized actin patches. Overexpression of the PRK1 gene in wild-type cells leads to lethality and actin cytoskeleton abnormalities similar to those exhibited by the pan1 and end3 mutants. In vitro phosphory lation assays demonstrate that Prk1p is able to phosphorylate regions of Pa n1p containing the LxxQxTG repeats, including the region responsible for bi nding to End3p. Based on these findings, we propose that the Prk1 protein k inase regulates the actin cytoskeleton organization by modulating the activ ities of some actin cytoskeleton-related proteins such as Pan1p/End3p.