p70 S6 Kinase: Proteins and Enzymes

p70 S6 kinase is a Ser/Thr kinase activated by such mitogens as EGF, IGF-I, and insulin. The S6 protein of the 40S ribosomal subunit is a major substrate of p70 S6 kinase, and its phosphorylation upregulates the translation of mRNAs containing an oligopyrimidine tract at their transcriptional start site. The activity of p70 S6 kinase is controlled by multiple phosphorylation events, with phosphorylation at T229 by PDK1 and T389 by mTOR most critical for kinase function.