Expression of Wild-type and Mutant Subunits of the cAMP-dependent Protein Kinase

Abstract

Protein phosphorylation provides the cell with a rapidly reversible mechanism for altering the activity of specific proteins in response to hormones or other extracellular or intracellular signals. All of the well-characterized intracellular second messengers act either directly to modulate protein kinases or indirectly to affect the levels of other activators of cellular kinases or inhibitors of protein phosphatases. Both cAMP and cGMP directly activate specific protein kinases, and Ca++ and diacylglycerol activate the protein kinase C (PKC) family of kinases (Knopf et al. 1986). Ca++, through interaction with calmodulin (CaM), also activates a small family of CaM-dependent kinases, some of which have a limited substrate spectrum, such as myosin light-chain kinase, and others, like Ca++/CaM-dependent kinase II, that recognize many substrates (for review, see Edelman et al. 1987). Many growth factors and hormones interact with cell-surface receptors that have protein tyrosine kinase activity (e.g., EGF and insulin receptors), and their...