Dept of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
Many bacteria communicate by secreting and responding to extracellular peptides (pheromones). Some peptide pheromones act via receptors on the cell surface, which are often membrane-bound histidine protein kinases. Other peptide pheromones are transported into the cell by an oligopeptide permease and interact with intracellular receptors to modulate gene expression.