This bacterial family of integral membrane proteins represents a positive regulator of the sigma(E) transcription factor, namely RseC/MucC. The sigma(E) transcription factor is up-regulated by cell envelope protein misfolding, and regulates the expression of genes that are collectively termed ECF (devoted to Extra-Cellular Functions) [1]. In Pseudomonas aeruginosa, de-repression of sigma(E) is associated with the alginate-overproducing phenotype characteristic of chronic respiratory tract colonisation in cystic fibrosis patients. The mechanism by which RseC/MucC positively regulates the sigma(E) transcription factor is unknown. RseC is also thought to have a role in thiamine biosynthesis in Salmonella typhimurium [2]. In addition, this family also includes an N-terminal part of RnfF, a Rhodobacter capsulatus protein, of unknown function, that is essential for nitrogen fixation. This protein also contains an ApbE domain Pfam:PF02424, which is itself involved in thiamine biosynthesis.

1: Modulation of the Escherichia coli sigmaE (RpoE) heat-shock transcription-factor activity by the RseA, RseB and RseC proteins. Missiakas D, Mayer MP, Lemaire M, Georgopoulos C, Raina S; Mol Microbiol 1997;24:355-371. PMID:9159522

2: Evidence that rseC, a gene in the rpoE cluster, has a role in thiamine synthesis in Salmonella typhimurium. Beck BJ, Connolly LE, De Las Penas A, Downs DM; J Bacteriol 1997;179:6504-6508. PMID:9335303

3: Identification of a new class of nitrogen fixation genes in Rhodobacter capsulatus: a putative membrane complex involved in electron transport to nitrogenase. Schmehl M, Jahn A, Meyer zu Vilsendorf A, Hennecke S, Masepohl B, Schuppler M, Marxer M, Oelze J, Klipp W; Mol Gen Genet 1993;241:602-615. PMID:8264535