Catalytic domain of the Serine/Threonine protein kinase, Fungal Casein Kinase 1 homolog 1
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. CK1 phosphorylates a variety of substrates including enzymes, transcription and splice factors, cytoskeletal proteins, viral oncogenes, receptors, and membrane-associated proteins. There are mutliple isoforms of CK1 and in mammals, seven isoforms (alpha, beta, gamma1-3, delta, and epsilon) have been characterized. These isoforms differ mainly in the length and structure of their C-terminal non-catalytic region. This subfamily is composed of fungal CK1 homolog 1 proteins, also called Yck1 in Saccharomyces cerevisiae and Cki1 in Schizosaccharomyces pombe. Yck1 (or Yck1p) and Cki1 are plasma membrane-anchored proteins. Yck1 phosphorylates and regulates Khd1p, a RNA-binding protein that represses translation of bud-localized mRNA. Cki1 phosphorylates and regulates phosphatidylinositol (PI)-(4)P-5-kinase, which catalyzes the last step in the sythesis of PI(4,5)P2, which is involved in actin cytoskeleton remodeling and membrane traffic. The fungal CK1 subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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