Protein Phosphorylation as a Regulatory Mechanism

The topics covered so far have included detailed considerations of the mechanism of protein synthesis in eukaryotes and of the numerous post-translational events which can affect the fate of newly synthesized polypeptide products. Post-translational phosphorylation of proteins is a widely occurring phenomenon which, since it is often readily reversible, can have important regulatory significance for numerous cellular activities. Included among these activities is the process of protein synthesis itself, so that in a sense we can reckon to have turned full circle in considering protein phosphorylation in relation to translation. Boyd Hardesty’s paper, in the translational initiation section, and my own contribution here both deal with aspects of protein phosphorylation as a translational control mechanism. It is clear that several proteins involved in the machinery of protein synthesis, most notably initiation factor eIF-2 and ribosomal protein S6, undergo a dynamic process of phosphorylation and that the extent to which a given site on a peptide chain is modified depends on the balance between specific kinase and phosphatase activities. The protein kinases are complex enough, but the protein phosphatases are even less well defined yet in terms of their structures, regulation and substrate specificities. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.