cdc25+ functions as an inducer in the mitotic control of fission yeast

Triggering the all-or-nothing switch into mitosis

“…In S. pombe, Wee1 is the major (but not exclusive) contributor to Y15 phosphorylation (Box 1): in its absence, G2 is shortened and cells divide when they are smaller, whereas Wee1 overproduction prolongs G2 ( Refs 21 and 22 ). Reciprocally, loss of function of Cdc25, the phosphatase that removes the inhibitory phosphate, arrests cells in G2, and its overexpression drives G2 cells into mitosis 23 . Finally, expression of a mutant form of Cdk1 that is immune to inhibitory phosphorylation bypasses the need for Cdc25 and causes cells to escape G2 prematurely 12 .…”

Mis3 with a conserved RNA binding motif is essential for ribosome biogenesis and implicated in the start of cell growth and S phase checkpoint

“…If coordinating control between cell mass and cell cycle is abolished, cells may enter a lethal stage with activation of CDK (cyclin dependent kinase) before reaching normal cell size (Lundgren et al 1991;Enoch et al 1992). It is known that tyrosine phosphorylation at Y15 controls the Cdc2 kinase activity and is important for cell cycle control (Russell & Nurse 1986. This site is phosphorylated by negatively acting Wee1 and Mik1 (a functional homologue of Wee1) kinases and is dephosphorylated by positively acting Cdc25 phosphatase.…”

The three postblastoderm cell cycles of Drosophila embryogenesis are regulated in G2 by string

“…Our studies of the string (stg) gene, however, offer a simple molecular explanation for the switch occurring in interphase 14 . stg encodes a protein belonging to a conserved family of mitotic regulators, the best studied of which is cdc25 of fission yeast (Fantes, 1981;Russell and Nurse, 1986;Russell et al, 1989;Sadhu et al, 1990;Ducommun et al, 1990). cdc25 is one of several factors, including cyclins, that are required to activate a highly conserved mitotic kinase, p34 cdc2 Gould and Nurse, 1989).…”