biostudies-literatureUnknown194(5)Dogra GRetrophosphorylation of the histidine kinase CheA in the chemosensory transduction chain is a widespread mechanism for efficient dephosphorylation of the activated response regulator. First discovered in Sinorhizobium meliloti, the main response regulator CheY2-P shuttles its phosphoryl group back to CheA, while a second response regulator, CheY1, serves as a sink for surplus phosphoryl groups from CheA-P. We have identified a new component in this phospho-relay system, a small 97-amino-acid protein named CheS. CheS has no counterpart in enteric bacteria but revealed distinct similarities to proteins of unknown function in other members of the α subgroup of proteobacteria. Deletion of cheS causes a phenotype similar to that of a cheY1 deletion strain. Fluorescence microscopy revealed that Journal of bacteriology1075-87https://www.ebi.ac.uk/biostudies/studies/S-EPMC3294773biostudies-literatureSinorhizobium meliloti CheA complexed with CheS exhibits enhanced binding to CheY1, resulting in accelerated CheY1 dephosphorylation.PMC3294773Dogra GPurschke FGRay WKScharf BEKriehuber TNiemeyer MGilbert CWagner VHughes JGHelm RFHaslbeck MVan Tassell MLfalseSinorhizobium meliloti CheA complexed with CheS exhibits enhanced binding to CheY1, resulting in accelerated CheY1 dephosphorylation.Retrophosphorylation of the histidine kinase CheA in the chemosensory transduction chain is a widespread mechanism for efficient dephosphorylation of the activated response regulator. First discovered in Sinorhizobium meliloti, the main response regulator CheY2-P shuttles its phosphoryl group back to CheA, while a second response regulator, CheY1, serves as a sink for surplus phosphoryl groups from CheA-P. We have identified a new component in this phospho-relay system, a small 97-amino-acid protein named CheS. CheS has no counterpart in enteric bacteria but revealed distinct similarities to proteins of unknown function in other members of the α subgroup of proteobacteria. Deletion of cheS causes a phenotype similar to that of a cheY1 deletion strain. Fluorescence microscopy revealed that 2012-01-01T00:00:00Z2012 Mar2026-05-01T17:21:18.492Z2026-04-07T17:05:08.081ZS-EPMC32947732219445410.1128/jb.06505-1110.1128/JB.06505-11