INACTIVATION OF THE CDC25 GENE-PRODUCT IN SACCHAROMYCES-CEREVISIAE LEADS TO A DECREASE IN GLYCOLYTIC ACTIVITY WHICH IS INDEPENDENT OF CAMP LEVELS

In the budding yeast Saccharomyces cerevisiae cyclic AMP (cAMP) can in fluence the activity of kev enzymes in carbohydrate metabolism through modulation of the activity of cAMP-dependent protein kinase. One of t he components involved in cAMP production is the CDC25 gene product, w hich can activate the RAS/adenylate cyclase pathway by promoting the e xchange of guanine nucleotides bound to RAS. In two yeast strains carr ying different thermosensitive alleles of the CDC25 gene, cAMP levels respond differently to an increase in growth temperature from 23-degre es-C (permissive) to 36-degrees-C (restrictive). In strain OL86 (cdc25 -5) the estimated intracellular concentration of cAMP dropped after tr ansfer to restrictive temperature whereas in strain ts321 (cdc25-1) th e cAMP level rose under the same conditions. Despite the differences i n cAMP levels the glycolytic flux in the two mutants responded in a ve ry similar way to the shift from permissive to restrictive temperature ; after the increase in the incubation temperature, the specific glyco lytic flux in both cdc25-1 and cdc25-5 initially increased from about 300 nmol min-1 (mg protein)-1 to about 500 nmol min-1 (mg protein)-1 ( presumably mainly as a consequence of the increase in temperature), bu t then gradually fell to 100-200 nmol min-1 (mg protein)-1. A similar pattern of CO2 production to that found in the two cdc25 mutants was a lso observed for several other thermosensitive mutants displaying a St art-II type of G1 arrest. In contrast, in a wild-type strain and in st rains giving a Start-I type of G1 arrest, CO2 production did not drop after a temperature shift. The specific activities of glycolytic enzym es in the two cdc25 mutants did not show much change after the tempera ture shift, indicating that the decrease in glycolytic flux was not ca used by a decrease in the activity of any of the glycolytic enzymes. O ur data show that, at least in long-term regulation, the cAMP levels p er se are not likely to be a prime factor controlling glycolytic flux.