Mutational analysis of the Bacillus subtilis DegU regulator and its phosphorylation by the DegS protein kinase

The DegS-DegU protein kinase-response regulator pair controls the expression of genes encoding degradative enzymes as well as other cellular functions in Bacillus subtilis. Both proteins were purified. The DegS protein was autophosphorylated and shown to transfer its phosphate to the DegU protein. Phosphoryl transfer to the wild-type DegU protein present in crude extracts was shown by adding 32P-labeled DegS to the reaction mixture. Under similar conditions, the modified proteins encoded by the degU24 and degU31 alleles presented a stronger phosphorylation signal compared with that of the wild-type DegU protein. This may suggest an increased phosphorylation of these modified proteins, responsible for the hyperproduction of degradative enzymes observed in the degU24 and degU31 mutants. However, the degU32 allele, which also leads to hyperproduction of degradative enzymes, encodes a modified DegU response regulator which seems not to be phosphorylatable. The expression of the hyperproduction phenotype of the degU32 mutant is still dependent on the presence of a functional DegS protein. DegS may therefore induce a conformational change of the degU32-encoded response regulator enabling this protein to stimulate degradative enzyme synthesis. Two alleles, degU122 and degU146, both leading to deficiency of degradative enzyme synthesis, seem to encode phosphorylatable and nonphosphorylatable DegU proteins, respectively.