COMPONENTS OF HISTIDINE TRANSPORT: HISTIDINE-BINDING PROTEINS AND hisP PROTEIN

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Abstract
The high-affinity ( K m = 3 × 10 -8 M) transport system for histidine in Salmonella typhimurium has been resolved into three components: J, K, and P. J, which is a histidine-binding protein released by osmotic shock, is specified by the hisJ gene: hisJ mutants lack the binding protein and are defective in histidine transport. Another class of mutants— dhuA , which is closely linked to hisJ —has five times the normal level of binding protein and has an increased rate of histidine transport. P, which is a protein specified by the hisP gene, is required for J binding protein to be operative in transport. hisP mutants, though defective in transport, have normal levels of J binding protein. K, a third transport component, works in parallel to J, and also requires the P protein in order to be operative in transport. A second histidine-binding protein has been found but its relation to K is unclear. hisJ, dhuA, and hisP have been mapped and are in a cluster (near purF ) on the S. typhimurium chromosome.