SWE1

Swe1, also known as Swe1p, is a protein kinase found in the budding yeast Saccharomyces cerevisiae. It belongs to the Wee1 family of tyrosine kinases and plays a key role in regulating the G2/M transition of the cell cycle. The primary function of Swe1 is to inhibit the cyclin-dependent kinase Cdc28 (Cdk1) by phosphorylating it on a conserved tyrosine residue, thereby delaying entry into mitosis.

Swe1 operates within the morphogenesis checkpoint, a surveillance pathway that ensures proper bud formation and cell polarity before mitosis proceeds. When cells experience defects in morphogenesis or bud development, Swe1 activity or stability increases, maintaining Cdc28 in its inactive, phosphorylated state and extending the G2 phase. The opposing action is provided by Mih1, the Cdc25 phosphatase in yeast, which removes the inhibitory phosphate and promotes mitotic entry.

Regulation of Swe1 is multi-layered, involving changes in protein stability, localization, and phosphorylation status. Under normal conditions, Swe1 is kept at low levels or rapidly degraded as cells approach mitosis. Genetic studies show that SWE1 is nonessential, but loss of SWE1 can lead to premature mitotic entry and abnormal cell morphology, especially under stress or morphogenesis-impaired conditions.

In summary, Swe1p functions as a Wee1-like kinase that enforces the morphogenesis checkpoint in budding yeast by inhibiting Cdc28 to ensure cells do not prematurely enter mitosis before proper bud development. It is encoded by the SWE1 gene.