The mpt regulator MptR contains two PTS regulatory domains (PRDs) flanking an EIIA domain like its homologs, ManR of ACY-1215 Listeria innocua and the well studied LevR of B. subtilis [13, 56, 57]. Phosphorylation in EIIA of LevR mediated by HPr-His-P leads to activation of lev transcription, while phosphorylation of PRD-II at His-869 by
the specific PTS EIIBLev negatively regulates transcription. Based on mutation analyses it was suggested that mpt transcription in L. innocua is similarity regulated by phosphorylation of ManR, and that phosphorylation Smoothened Agonist in vivo at both sites would also downregulate mpt transcription . Such a model can be reconciled with our findings on mpt transcription regulation in E. faecalis, and in the mptD-inactivated mutant EIIABMpt will phosphorylate MptR (at PRD-II) and thereby negatively regulate transcription
of its own operon. We cannot exclude that the weak mpt signals of MOM1 are caused by altered mRNA stability. Reduced expression was also seen for EF0024 located downstream of mptD, indicating it being a part of the mpt operon. This gene is highly conserved downstream the mannose PTS genes in lactic acid bacteria, Listeria and Clostridium, and it is down-regulated in a σ54-mutant of L. monocytogenes, implying that it is part of the mannose PTS operon also in this organism . The mph operon is regulated by another σ54-depending U0126 regulator, encoded by EF1955 , which has a domain architecture similar to MptR and LevR and the phosphorylatable histidines are
conserved among the three regulators. The up-regulation of the mph operon seen in our mutants can probably be ascribed to activation of the regulator by phosphorylation of its EIIAMph-domain (His-566) by HPr-His-P. Such activation would be prevented in the wild type growing on glucose . HPr-His-P can control transcription dependent on regulators containing PTS domains and PRDs . Two PRD containing antiterminator proteins were identified in the E. faecalis genome, and enhanced expressions was observed for one (EF1515), along with the downstream gene encoding an N-acetylglucosamine-specific Methocarbamol EIIABC, a multidomain PTS protein. Regulators of this BigG-family cause release of termination structures in mRNA and enhanced transcription of downstream PTS genes when activated by HPr-His-P [59, 60], which can explain the increased gene expression in the mutants. In an analogous manner, the increased expression seen for the ascorbate-specific EIIB and EIIC genes are possibly caused by HPr-His-P mediated phosphorylation of the regulator encoded by the upstream EF2966. The EF2966 gene product contains PRDs and PTS domains and is probably a transcription regulator, but has erroneously been annotated as a BglG-type antiterminator although it lacks an RNA-binding domain .