ANTAGONISTIC EFFECTS OF DUAL PTS-CATALYZED PHOSPHORYLATION ON THE BACILLUS-SUBTILIS TRANSCRIPTIONAL ACTIVATOR LEVR

LevR, which controls the expression of the lev operon of Bacillus subt ilis, is a regulatory protein containing an N-terminal domain similar to the NifA/NtrC transcriptional activator family and a C-terminal dom ain similar to the regulatory part of bacterial anti-terminators, such as BglG and LicT, Here, we demonstrate that the activity of LevR is r egulated by two phosphoenolpyruvate (PEP)-dependent phosphorylation re actions catalysed by the phosphotransferase system (PTS), a transport system for sugars, polyols and other sugar derivatives. The two genera l components of the PTS, enzyme I and HPr, and the two soluble, sugar- specific proteins of the lev-PTS, LevD and LevE, form a signal transdu ction chain allowing the PEP-dependent phosphorylation of LevR, presum ably at His-869, This phosphorylation seems to inhibit LevR activity a nd probably regulates the induction of the lev operon. Mutants in whic h His-869 of LevR has been replaced with a nonphosphorylatable alanine residue exhibited constitutive expression from the lev promoter, as d o levD or levE mutants. In contrast, PEP-dependent phosphorylation of LevR in the presence of only the general components of the PTS, enzyme I and HPr, regulates LevR activity positively. This phosphorylation m ost probably occurs at His-585, Mutants in which His-585 has been repl aced with an alanine had lost stimulation of LevR activity and PEP-dep endent phosphorylation by enzyme I and HPr, This second phosphorylatio n of LevR at His-585 is presumed to play a role in carbon catabolite r epression.