The cdr2(+) Gene Encodes a Regulator of G(2)/M Progression and Cytokinesis in Schizosaccharomyces pombe

Schizosaccharomyces pombe cells respond to nutrient deprivation by altering G(2)/M cell size control. The G(2)/M transition is controlled by activation of the cyclin-dependent kinase Cdc2p. Cdc2p activation is regulated both positively and negatively. cdr2(+) was identified in a screen for regulators of mitotic control during nutrient deprivation. We have cloned cdr2(+) and have found that it encodes a putative serine-threonine protein kinase that is related to Saccharomyces cerevisiae Gin4p and S. pombe Cdr1p/Nim1p. cdr2(+) is not essential for viability, but cells lacking cdr2(+) are elongated relative to wild-type cells, spending a longer period of time in G(2). Because of this property, upon nitrogen deprivation cdr2(+) mutants do not arrest in G(1), but rather undergo another round of S phase and arrest in G(2) from which they are able to enter a state of quiescence. Genetic evidence suggests that cdr2(+) acts as a mitotic inducer, functioning through wee1(+), and is also important for the completion of cytokinesis at 36°C. Defects in cytokinesis are also generated by the overproduction of Cdr2p, but these defects are independent of wee1(+), suggesting that cdr2(+) encodes a second activity involved in cytokinesis.