This report is the last one concerning work on the induction of mitosis and meiosis in the yeast Saccharomyces cerevisiae and the characterization of nuclear proteins in yeast and mouse cells. Previously, we had found that meiosis is initiated by the specific decrease of GTP. We have now shown that this initiation does not require a change in the concentration of cAMP and that GTP deprivation also causes an increase in the synthesis of glycogen. cAMP also does not mediate catabolite repression. But the presence of a carbon source is required for the normal completion of spores. Since the RASval gene prevents sporulation of yeast during nitrogen starvation, we have constructed a gua RASval double mutant; it cannot sporulate or produce glycogen during guanine deprivation which shows that the RASval mutation is always dominant. We have also characterized nuclear matrix proteins and isolated the cDNA gene for one of them from a mouse brain cDNA library.
