Identification of a membrane protein as a histidine transport component in Salmonella typhimurium

A component of high-affinity histidine transport in Salmonella typhimurium has been identified. It is a basic (pI about 9.0) membrane-bound protein, the P protein. It is shown to be coded for by the distal half of the previously described hisP gene by analysis of numerous hisP mutants, two of which exhibit P proteins with altered electrophoretic mobilities. Upon separation of the cytoplasmic (inner) from the outer membrane, it can be shown that the P protein is located in the cytoplasmic membrane. The P protein is under the same regulatory controls as histidine transport--i.e., transport operon promoter dhuA and nitrogen regulation. A wild-type cell contains about 200 molecules of P protein. As a result of this work we now divide the hisP gene into two genes: the hisP gene proper and the hisQ gene, which codes for another essential component of histidine transport, the Q protein. The P protein was shown previously by genetic analysis to interact with the periplasmic histidine-binding protein J, another essential component of histidine transport. Possible mechanism for the interaction of the J, P, and Q components in histidine transport, and of P and Q in lysine/arginine/ornithine transport, are discussed.