| Abstract: | Aspartate transcarbamylase is synthesized during exponential growth of Bacillus subtilis and is inactivated when the cells enter the stationary phase. This work is a study of the regulation of aspartate transcarbamylase synthesis during growth and the stationary phase. Using specific immunoprecipitation of aspartate transcarbamylase from extracts of cells pulse-labeled with tritiated leucine, we showed that the synthesis of the enzyme decreased very rapidly at the end of exponential growth and was barely detectable during inactivation of the enzyme. Synthesis of most cell proteins continued during this time. When the cells ceased growing because of pyrimidine starvation of a uracil auxotroph, however, synthesis and inactivation occurred simultaneously. Measurement of pools of pyrimidine nucleotides and guanosine tetra- and pentaphosphate demonstrated that failure to synthesize aspartate transcarbamylase in the stationary phase was not explained by simple repression by these compounds. The cessation of aspartate transcarbamylase synthesis may reflect the shutting off of a "vegetative gene" as part of the program of differential gene expression during sporulation. However, aspartate transcarbamylase synthesis decreased normally at the end of exponential growth at the nonpermissive temperature in a mutant strain that is temperature-sensitive in sporulation and RNA polymerase function. Cessation of aspartate transcarbamylase synthesis appeared to be normal in three other temperature-sensitive RNA polymerase mutants and in several classes of spo0 mutants. |
