Reversible Protein Phosphorylation in Cell Regulation

2 During our formative years with Dr. Krebs at Davis, ed until the ER becomes substantially depleted of Ca +. California, we (c. and M. Brostrom) were imbued with For example, acute exposure of GH3 pituitary cells to 2 2 our continuing interest in the roles of Ca+ and cAMP in Ca+ ionophore A23187 or EGTA has been found to re­ biological control mechanisms. We remember our time sult in the inhibition of amino acid incorporation. disap­ with Dr. Krebs with great affection both for his intense pearance of polysomal content with accumulation of interest and high standards in science and for his great monosomes and ribosomal subunits. sharp reduction of decency in the treatment of postdoctoral fellows. We the cellular content of 43S pre initiation complex. and have subsequently aspired, within the constraints of our the phosphorylation of elF-2ex and inhibition of eIF-2B ability, to pattern our behavior in accord with this expe­ [15-17]. Neither translational elongation nor peptide rience. Our current research involving the control of chain termination appeared to be affected in these ex­ protein synthesis at mRNA translation embodies much periments, since average ribosomal transit times and the methionylation of tRNA;met were not altered. Amino of the familiar in protein phosphorylation with some new twists that we shall highlight in this article with our acid incorporation was unaffected during the period of 2 associate. Dr. Prostko. Ca+ release prior to suppression of initiation.