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Catalytic domain of the Serine/Threonine Kinase, 70 kDa ribosomal protein S6 kinase STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. p70S6K (or S6K) contains only one catalytic kinase domain, unlike p90 ribosomal S6 kinases (RSKs). It acts as a downstream effector of the STK mTOR (mammalian Target of Rapamycin) and plays a role in the regulation of the translation machinery during protein synthesis. p70S6K also plays a pivotal role in regulating cell size and glucose homeostasis. Its targets include S6, the translation initiation factor eIF3, and the insulin receptor substrate IRS-1, among others. Mammals contain two isoforms of p70S6K, named S6K1 and S6K2 (or S6K-beta). The p70S6K 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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