Involvement of the Stringent Response in Regulation of Protein Degradation in Bacillus subtilis

Abstract

This chapter discusses presents various experiments conducted on Bacillus subtilis and various characteristics of Bacillus subtilis . Bulk protein turnover is substantially reduced during amino acid starvation of relaxed E. coli mutants, as compared to isogenic rel + strains. Certain studies have revealed that the loss of ATCase activity is paralleled exactly by the loss of cross-reactive protein and that the cross-reactive protein is degraded. Evidence that the stringent response regulates the degradation of ATCase in B. subtilis was obtained from a study of the stability of the enzyme in rel + and rel - mutants. The degradation of an enzyme of pyrimidine biosynthesis in starving B. subtilis cells presumably serves the physiological role of committing such cells to synthesis of new nucleic acid solely at the expense of turnover of old nucleic acids. Protein degradation may be regulated by rel -dependent and rel -independent pathways, and the relative contribution of each pathway depends on both the stimulus applied and the particular protein being degraded. Degradation of amidotransferase apparently follows an oxidative inactivation; no preliminary inactivation has been found in the case of ATCase. As oxidized, inactive amidotransferase is physically altered and more susceptible than native enzyme to proteolysis, it is probably subject to degradation by multiple pathways after inactivation.