| Abstract: | The rate of total protein degradation down to acid-soluble products in the B. subtilis cells growing on a minimal medium is about 4--5% per hour. Under amino acid deficiency the rate of proteolysis depends on the allelic state of the relA gene, so that in the rel+ cells it increases two-fold, while in the rel- cells it remains low. Elimination of NH4+, PO43- and Mg2+ from the culture medium or an addition of NaN3 (8 mM) or 2,4-dinitrophenol (2 mM) results in 1.5--2.0-fold stimulation of proteolysis independently of the relA gene. In all cases studied the rate of proteolysis decreases after addition of chloramphenicol (100 micrograms/ml). It is proposed that chloramphenicol decreases the intracellular concentration of ppGpp, which is believed to exert pleiotropic alterations of cellular metabolism under condition of growth limitation. Quite different is the case of degradation of anomalous proteins synthesized in the presence of the lysine analog--S-2-aminoethylcystein. Degradation of anomalous proteins proceeds very rapidly (about 70% per hour); chloramphenicol (100 micrograms/ml) decreases the rate of proteolysis only two-fold. It was found that tetracycline (100 micrograms/ml) effectively inhibits the degradation of anomalous proteins. This activity of tetracycline was not observed in the presence of 50 mM of Mg2+ and seems to be dependent on the capacity of the antibiotic to form complexes with bivalent cations. These results reveal common features of control of proteolysis in the cells of B. subtilis and E. coli. |
