Cell cycle and growth regulation in RAS2 mutant cells of Saccharomyces cerevisiae

Yeast cells carrying ras2 temperature-sensitive mutations undergo a specific arrest in the prereplicative unbudded phase of the cell cycle when they are shifted to non-permissive temperatures. At 36.5 degrees C, in spite of their abnormally large cell size, bulk protein synthesis and accumulation rates are depressed in ras2 temperature-sensitive cells in comparison with isogenic wild type. At the same temperature, total RNA synthesis and accumulation rates are much more inhibited, suggesting that a defective Ras2/cAMP pathway alters the coordination between RNA and protein synthesis rates. The preferential RNA synthesis inhibition is correlated to a specific inhibition of the synthesis of the 35S rRNA precursor. These findings, taken together with the results of previous analyses, are in favour of a control by the cAMP pathway on rRNA biosynthesis.