Positively regulates the expression of the mannose operon that consists of three genes, manP, manA, and yjdF, which are responsible for the transport and utilization of mannose. Also activates its own expression. D-mannose(out) + N(pros)-phospho-L-histidyl-[protein] = D-mannose 6-phosphate(in) + L-histidyl-[protein] The regulatory activity of ManR is modulated by phosphorylation and dephosphorylation of the various ManR domains. It becomes activated via phosphoryl group transfer from PEP, EI and HPr on the two conserved histidine residues in the PRD 2 domain, whereas phosphorylation of the EIIA-like domain on His-570 by the PTS EIIB-Man domain of ManP inactivates ManR (PubMed:23551403). Up-regulated by mannose. Is subject to carbon catabolite repression (CCR) by glucose. Cells lacking this gene are unable to grow with mannose as the sole carbon source. Belongs to the transcriptional antiterminator BglG family.