We have found that in the yeast, Saccharomyces cerevisiae, nutritional deprivation, which leads to Go arrest and conformational changes in folded chromosome complexes, also results in the phosphorylation of a number of folded chromosome associated proteins (FCAP). These observations suggest that, as in mammalian cells, protein phosphorylation in yeast may be a general mechanism by which external stimuli control cellular proliferation. We propose here to initiate a detailed study of the nature of the phosphorylation pathway, the signals to which it responds, and the role that chromosomal phosphoproteins may hve in regulating chromosome structure and gene activity. We propose: (1) to examine the specificity and generality of protein phosphorylation in response to different arrest signals, specifically, by (a) deprivation for compounds required for cellular proliferation and modulation and carbon catabolite repression, (b) matingpheromone induced cell cycle arrest, and (c) cell cycle arrest in cell-division-cycle (cdc) mutants. The phosphorylation of individual FACP and their respective phosphoamine acid content will be measured by two-dimensional acrylamide gel electrophoresis, autoradiography, and thin-layer chromatography. (2) to purify and begin the characterization of the major alkali stable Go-specific phosphorylated FCAP and their respective protein kinases. Affinity chromatograph (Hg-Sepharase and phosphotyrosine antibody-Sepharase) will be used to purify the phosphoproteins; filter binding and DNA-protection assays will be used to study the DNA binding characteristics of the purified proteins. Phosphothioate-substituted ATP, Hg-sepharase affinity chromatography, and SDS-gel electrophoresis will be used to assay and characterize the nutritionally responsive protein kinases. (3) to raise antisera against purified phosphoproteins to study their synthesis, and to probe other species for immunologically related proteins to test for sequence and structural conservation.
