Chemoreceptors in Escherichia coli control the activity of a kinase that phosphorylates a response regulator that, in turn, biases the direction of rotation of flagellar motors, affecting the manner in which cells swim. A small change in receptor occupancy induces a large change in kinase activity. This gain is generated by allosteric interactions between receptors, which are arranged in clusters. The idea that such amplification might occur was advanced by Dennis Bray in 1998, and confirmed experimentally in 2002.