<p> This histidine kinase protein is paired with an adjacent response regulator (<db_xref db="TIGRFAMS" dbkey="TIGR03787"/>) gene. It co-occurs with a variant sortase enzyme (<db_xref db="TIGRFAMS" dbkey="TIGR03784"/>), usually in the same gene neighbourhood, in proteobacterial species most of which are marine, and with an LPXTG motif-containing sortase target conserved protein (<db_xref db="TIGRFAMS" dbkey="TIGR03788"/>). Sortases and LPXTG proteins are far more common in Gram-positive bacteria, where sortase systems mediate attachment to the cell wall or cross-linking of pilin structures. We give this predicted sensor histidine kinase the gene symbol psdS, for Proteobacterial Dedicated Sortase system Sensor histidine kinase. </p>