part of phosphorelay sensor kinase activity https://github.com/geneontology/go-ontology/issues/28061 https://github.com/geneontology/go-ontology/issues/28520 two-component sensor molecule GO:0000155 molecular_function two-component sensor activity two-component system sensor activity Catalysis of the phosphorylation of a histidine residue in response to detection of an extracellular signal such as a chemical ligand or change in environment, to initiate a change in cell state or activity. The two-component sensor is a histidine kinase that autophosphorylates a histidine residue in its active site. The phosphate is then transferred to an aspartate residue in a downstream response regulator, to trigger a response. phosphorelay signal transduction system protein histidine kinase activity molecular sensor activity