Carbon and Energetic Uncoupling Are Associated with Block of Division at Different Stages of the Cell Cycle in Several cdc Mutants of Saccharomyces cerevisiae

Abstract

Cell proliferation arrest at 37°C (restrictive temperature) of the cell division cycle (cdc) mutants of Saccharomyces cerevisiae cdc28, cdc35, cdc19, cdc21, and cdc17 was correlated with carbon and energy uncoupling. At 37°C, cdc mutants diverted to biomass synthesis only 3 to 4% and 8 to 24% of the fluxes of carbon consumed and ATP obtained by catabolism, respectively, compared with 48 and 34% in the wild-type strain A364A. At the permissive temperature (25°C), the wild type showed similar carbon and energy coupling indexes as at 37°C. However, carbon and energy coupling indexes were two- to sevenfold higher at 25° than at 37°C in cdc mutants; e.g., at 25°C two- to seven-fold higher amounts of carbon and ATP were directed to biomass production than at 37°C. The wild-type strain exhibited a purely oxidative glucose catabolism at 37°C (RQ ∼ 1.0), while the cell proliferation arrest of cdc mutants at the same temperature was characterized by fermentative metabolism. At 37°C, cdc mutants directed 50 to 60% of the carbon to ethanol production; 3 to 12% of the carbon was recovered as glycerol in cdc mutants as well as in the wild type. The proliferation arrest of the cell division cycle mutant cdc28 correlated with a significant decrease in the incorporation of radio-active precursors into DNA, RNA, and proteins. In the presence of 8-hydroxyquinoline, the wild-type strain underwent cell proliferation arrest and also exhibited metabolic uncoupling with bioenergetic and catabolic behavior similar to that of the cdc mutants at 37°C. Experimental evidence obtained with cdc19, whose defective gene product is pyruvate kinase, suggests that the primary defect of cdc mutants correlates with a metabolically, highly uncoupled yeast cell. The results presented point to the existence of strong carbon and energy uncoupling together with cell division arrest exhibited by cdc mutants at the restrictive temperature. The degree of uncoupling appears to be tuned, at least in part, by the increase in flux of sugar catabolism through the ethanol fermentative pathway.