The models of the R. sphaeroides chemotaxis system. The different connecitvities modelled for CheY3 and CheY4 are shown in this diagram. The coloured lines represent three models presented in this paper. In the blue model CheY3-P and CheY4-P bind to FliM in the motor co-operatively with CheY6-P. In the red model CheY3 and CheY4 form a connection with the cytoplasmic cluster and act antagonistically to ligand in altering the kinase activity of CheA4; therefore, the increase in CheY3/4-P acts to increase the rate of CheA3 phosphorlyation by CheA4. In the magenta model CheY3/4 interact with CheA3 preventing CheY6 binding and hence phosphotransfer. The fourth model corresponds to a model, in which CheY3 and CheY4 act as phosphate sinks only and hence do not interact with anything. This is referred to as the grey model in this paper. It should be noted that the other three models also contain this interconnection and that the difference in the grey model is that only this connection exists.