Catalytic domain of the Protein Tyrosine Kinases, Fungal Wee1 proteins
PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. This subfamily is composed of fungal Wee1 proteins, also called Swe1 in budding yeast and Mik1 in fission yeast. Yeast Wee1 is required to control cell size. Wee1 is a cell cycle checkpoint kinase that helps keep the cyclin-dependent kinase CDK1 in an inactive state through phosphorylation of an N-terminal tyr (Y15) residue. During the late G2 phase, CDK1 is activated and mitotic entry is promoted by the removal of this inhibitory phosphorylation by the phosphatase Cdc25. Although Wee1 is functionally a tyr kinase, it is more closely related to serine/threonine kinases (STKs). It contains a catalytic kinase domain sandwiched in between N- and C-terminal regulatory domains. It is regulated by phosphorylation and degradation, and its expression levels are also controlled by circadian clock proteins. The fungal Wee1 subfamily is part of a larger superfamily that includes the catalytic domains of STKs, other PTKs, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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