A panel of six purified histidine kinases were tested using radioactive ATP32P and the ATPγS antibody assay. A) Coomassie stained gel of the panel of purified histidine kinases. B) Phosphorimage of radioactive gel showing the panel of histidine kinases tested using ATP32P. C) Western blot showing the panel of histidine kinases tested using the ATPγS antibody assay. Lane 1: T. maritima CheA, 2: E. coli NtrB and lanes 3–6: H-NOX associated kinases from S. oneidensis, L. pneumophila, H. chejuensis, and V. fischeri respectively. The molecular weights of the proteins are as follows: T. maritima CheA: 75.5 kDa, E. coli NtrB: 23.6 kDa, SO2144: 34.9 kDa, LPG2458: 49.2 kDa, HCH03701: 87.4 kDa, VFA0072: 65.3 kDa