Abstract
Formation of the complex between the 1st enzyme of histidine biosynthesis from Salmonella typhimurium, ATP phosphoribosyltransferase [1-(5.sbd.phosphoribosyl)-ATP: pyrophosphate phosphoribosyltransferase; EC 2.4.2.17] and histidyl-tRNA is inhibited by L-histidine and by guanosine-5''-diphosphate-3''-diphosphate in the presence of histidine. Higher histidine levels make guanosine tetraphosphate a more effective inhibitor. Relatively high concentrations of GTP also inhibit complex formation, but this inhibition is not enhanced by histidine. The possible implications of these observations in the gene regulatory activity of this enzyme are discussed.