Chemotactic-signal transducers respond to changes in the concentration of attractants and repellents in the environment, transduce a signal from the outside to the inside of the cell, and facilitate sensory adaptation through the variation of the level of methylation. McpU is a chemoreceptor that binds and mediates chemotaxis to polyamines such as putrescine, spermidine, cadaverine and agmatine (PubMed:26662997, PubMed:30425146). Also binds histamine and ethylenediamine with much lower affinities (PubMed:30425146). The ligand binding domain (LBD) is monomeric in solution. Ligand binding does not cause major conformational changes or alterations in the oligomeric state of the LBD. Mutant shows increased biofilm formation as compared to the wild type. Mutation decreases plant root colonization. Belongs to the methyl-accepting chemotaxis (MCP) protein family.