ABSTRACT
During exponential growth at temperatures of 30 to 39 degrees C, the specific activity of H(+)-ATPase in the plasma membrane of Saccharomyces cerevisiae (assayed at the standard temperature 30 degrees C) increased with increases in growth temperature. In addition, the optimal temperature for in vitro activity of this ATPase was 42 degrees C. Therefore, the maximum values of ATPase activity were expected to occur in cells that grew within the supraoptimal range of temperatures. Activation induced by supraoptimal temperatures was not the result of increased synthesis of this membrane enzyme. When the growth temperature increased from 30 to 40 degrees C, expression of the essential PMA1 gene, monitored either by the level of PMA1 mRNA or the beta-galactosidase activity of the lacZ-PMA1 fusion, was reduced. Consistently, quantitative immunoassays showed that the ATPase content in the plasma membrane decreased. Like ATPase activity, the efficiency of the PMA2 promoter increased with increases in growth temperature in cells that had been grown at 30 to 39 degrees C, but its level of expression was several hundred-fold lower than that of PMA1. These results suggest that the major PMA1 ATPase is activated at supraoptimal temperatures.
