Isolation and phosphorylation of the Bacillus subtilis degS and degU gene products

The Bacillus subtilis sacU locus consists of two genes, degS and degU, which positively regulate the synthesis of several extracellular enzymes including the neutral and alkaline proteases. Both the DegS and DegU proteins have been purified from overproducing Escherichia coli strains harboring degS or degU gene-carrying plasmids, and the following results were obtained. DegS was autophosphorylated in the presence of [gamma-32P]ATP, and transferred the phosphoryl group to DegU. The transfer reaction was rapid in contrast to the autophosphorylation reaction. The phosphoryl groups incorporated into DegS and DegU were released at their own specific rates, the latter being twice faster than the former. The linkage between DegS and the phosphoryl moiety was unstable at acidic pH, whereas reverse was the case for the linkage between DegU and its phosphoryl group, suggesting that His and Asp are involved in the formation of DegS-phosphate and DegU-phosphate, respectively. Deletion of degS resulted in the reduced expression of the exocellular alkaline protease gene, aprE. These results suggest that phosphorylation of DegS by its own kinase activity and subsequent transfer of the phosphoryl group to DegU play a role in the activation of the aprE gene.