Glucose and ras activity influence the ubiquitin ligases APC/C and SCF in Saccharomyces cerevisiae

In budding yeast, the Ras/cAMP pathway is involved in the coordination of cell growth and cell division. Glucose-rich medium stimulates Ras/cAMP signaling, which causes an increase in the critical cell size for cell cycle entry. Here we show that glucose and activated Ras proteins also influence the function of the anaphase-promoting complex (APC/C), a ubiquitin-protein ligase required for sister chromatid separation and mitotic exit. We found that apc10-22 and other mutants defective in the APC/C are suppressed by reduced Ras signaling activity, by a deletion of the RAS2 gene, by a cdc25 mutation, by elevated levels of PDE2, or by growth without glucose. Viability of these mutants is also enhanced by decreased Cdk1 activity. In contrast, a constitutively activated RAS2(Val19) allele or shifts to glucose medium are deleterious to apc10-22 mutants. Remarkably, cdc34-2 mutants, which are impaired in SCF function, are differently affected with respect to Ras activity. Viability of cdc34-2 mutants at elevated temperatures is dependent on glucose and the RAS2 gene. We conclude that glucose and Ras proteins influence the APC/C and the SCF complex in an opposite manner. These ubiquitin ligases might represent novel targets for modulating cell division in response to growth conditions.