FIG. 1.

Occurrence of chemotaxis proteins in prokaryotes. Black indicates the presence of MCPs, CheW, CheA, CheY, CheR, CheB, and CheD; red indicates CheC; green indicates hybrid Che proteins such as CheV; magenta indicates CheZ. Numbers to the right of each branch represent the number of completely or nearly completely sequenced genomes in which chemotaxis genes have been found. Alpha, beta, gamma, delta, and epsilon indicate subdivisions of Proteobacteria. Evolutionary distances are not drawn to scale. The cladogram represents general evolutionary trends. The particular set of chemotaxis genes in a given genome may be different due to gene loss and lateral gene transfer. For example, CheD and CheV are missing from E. coli but present in many other bacteria from the β/γ subdivision of Proteobacteria; laterally transferred CheC is found in 3 of 30 sequenced proteobacterial species. The figure was provided by I. Zhulin.