The casein kinases are cyclic nucleotide-independent protein kinases which are widely distributed among eukaryotic organisms. These enzymes phosphorylate a broad spectrum of substrates including translational initiation factors, acidic ribosomal proteins, membrane proteins, and chromosomal proteins. Protein kinases which phosphorylate many different protein substrates have generally been found to play important integrative roles in coordinating cell metabolism. This is true for cAMP-dependent kinase, which plays a central role in mediating cellular responses to hormonal stimuli, and for the tyrosine-specific kinases, which appear to be involved in control of cell growth. Although the function of the casein kinases is presently unknown, the substrate specificity of these enzymes suggests that they exert a regulatory influence on many important cellular functions, including translation, cell-cell recognition, transcription, and chromosome condensation. Furthermore, because the oncogenes of many RNA tumor viruses are tyrosine-specific kinases which are homologous to normal cellular enzymes, it is likely that abnormal functioning of protein kinases, including the casein kinases, can result in aberrant cell behavior and disease. The overall goal of the proposed research is to determine the physiological role of casein kinase II. Drosophila melanogaster has been chosen as the principal experimental organism for this work because of the potential for genetic studies in this species.
The specific aims of the research are: (1) to determine the functional consequences of specific phosphorylation events catalyzed by casein kinase II - these experiments will be carried out in vitro using the purified Drosophila enzyme and specific purified substrates; (2) to determine how the activity of casein kinase II is regulated - the significance of a high molecular weight, filamentous form of the enzyme will be examined; (3) to isolate and characterize genes coding for the two polypeptide subunits of casein kinase II - isolation of the genes will be accomplished using an antiserum prepared against the homogeneous Drosophila enzyme; and (4) to isolate mutants in order to determine whether casein kinase II is an essential enzyme in vivo and to investigate its function by genetic techniques - isolation of mutants will be accomplished using the cloned genes in combination with genetic techniques available in Drosophila.
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