The wis1 protein kinase is a dosage-dependent regulator of mitosis in Schizosaccharomyces pombe.

Abstract

The wis1+ gene encodes a newly identified mitotic control element in Schizosaccharomyces pombe. It was isolated by virtue of its interaction with the mitotic control genes cdc25, wee1 and win1. The wis1+ gene potentially encodes a 66 kDa protein with homology to the serine/threonine family of protein kinases. wis1+ plays an important role in the regulation of entry into mitosis, as it shares with cdc25+ and nim1+/cdr1+ the property of inducing mitosis in a dosage‐dependent manner. Increased levels of wis1+ expression cause mitotic initiation to occur at a reduced cell size. Loss of wis1+ function does not prevent vegetative growth and division, though wis1‐ cells show an elongated morphology, indicating that their entry into mitosis and cell division is delayed relative to wild type cells. wis1‐ cells undergo a rapid reduction of viability upon entry into stationary phase, suggesting a role for wis1+ in the integration of nutritional sensing with the control over entry into mitosis.

Fission Yeast Ste9, a Homolog of Hct1/Cdh1 and Fizzy-related, Is a Novel Negative Regulator of Cell Cycle Progression during G1-Phase

“…The total cell number increased 3.8 times for the wild-type strain and 4.4 times for the ste9 mutant, indicating that both strains passed through mitosis twice before they ceased to proliferate. We and others previously isolated several sterile mutants that rapidly lost viability after nutritional starvation (Kitamura et al, 1990;Devoti et al, 1991;Warbrick and Fantes, 1991;Takeda et al, 1995). To test whether the ste9 mutants normally responded to starvation, viability in longterm culture was monitored.…”

Schizosaccharomyces pombe gad7+ encodes a phosphoprotein with a bZIP domain, which is required for proper G1 arrest and gene expression under nitrogen starvation

“…3A, gad71 cells grew poorly on a plate containing 1 M KCl, although slightly better than wis11 cells examined as an osmosensitive control. The wis1 gene product, Wis1, is an osmosensing MAPKK homologue, and cells defective in wis1 can hardly grow on the medium supplemented with a high concentration of KCl (Warbrick & Fantes 1991;Millar et al 1995;Shiozaki & Russell 1995).…”

“…Wis1 is a putative MAPKK (Warbrick & Fantes 1991). Sty1/Spc1 has recently been reported to be a MAP kinase that functions downstream of Wis1 (Millar et al 1995;Shiozaki & Russell 1995).…”

“…One of them consists of Byr2(MAPKKK), Byr1(MAPKK) and Spk1(MAPK), and is involved in the mating pheromone signalling (Neiman et al 1993). The other is employed in the osmosensing pathway, and Wis1(MAPKK) and Sty1/Spc1(MAPK) participate in it (Warbrick & Fantes 1991;Millar et al 1995;Shiozaki & Russell 1995). The latter cascade is relevant to the control of timing of the entry into mitosis.…”

“…The latter cascade is relevant to the control of timing of the entry into mitosis. If the wis1 or sty1/spc1 gene is deleted, the cells become larger in size and are delayed in the entry into mitosis (Warbrick & Fantes 1991;Millar et al 1995;Shiozaki & Russell 1995). The target(s) of the MAP kinase has not been identified in either cascade.…”