THE HPR PROTEIN OF THE PHOSPHOTRANSFERASE SYSTEM LINKS INDUCTION AND CATABOLITE REPRESSION OF THE BACILLUS-SUBTILIS LEVANASE OPERON

The LevR protein is the activator of expression of the levanase operon of Bacillus subtilis, The promoter of this operon is recognized by RN A polymerase containing the sigma 54-like factor sigma(L), One domain of the LevR protein is homologous to activators of the NtrC family, an d another resembles antiterminator proteins of the BglG family. It has been proposed that the domain which is similar to antiterminators is a target of phosphoenolpyruvate:sugar phosphotransferase system (PTS)- dependent regulation of LevR activity. We show that the LevR protein i s not only negatively regulated by the fructose-specific enzyme IIA/B of the phosphotransferase system encoded by the levanase operon (lev-P TS) but also positively controlled by the histidine-containing phospho carrier protein (HPr) of the PTS. This second type of control of LevR activity depends on phosphoenolpyruvate-dependent phosphorylation of H Pr at histidine 15, as demonstrated with point mutations in the ptsH g ene encoding HPr. In vitro phosphorylation of partially purified LevR was obtained in the presence of phosphoenolpyruvate, enzyme I, and HPr . The dependence of truncated LevR polypeptides on stimulation by HPr indicated that the domain homologous to antiterminators is the target of HPr-dependent regulation of LevR activity, This domain appears to b e duplicated in the LevR protein. The first antiterminator-like domain seems to be the target of enzyme I and HPr-dependent phosphorylation and the site of LevR activation, whereas the carboxy-terminal antiterm inator-like domain could be the target for negative regulation by the lev-PTS.