Genetic analysis of the histidine operon in Escherichia coli K12.

I N Salmonella typhimurium a cluster of nine genes, behaving as a single operon (AMES and GARRY 1959) specify the enzymes which carry out the ten reactions involved in the biosynthesis of histidine; one of the nine enzymes is bifunctional (LOPER, GRABNAR, STAHL, HARTMAN and HARTMAN 1964). The histidine operon is contained in a linear segment of deoxyribonucleic acid (DNA) estimated by AMES, GOLDBERGER, HARTMAN, MARTIN and ROTH ( 1967) to be 1 1,000 base pairs in length (over three cell lengths). Fifteen cistrons have been sequenced and their enzyme products identified. Mutations leading to a requirement for histidine (his) in another enteric organism, Escherichia coli, have been found to cluster on its genetic map (TAYLOR and TROTTER 1967) at a position comparable to that of the histidine operon in Salmonella (SANDERSON 1967). The high degree of correspondence in the locations and functions of genes in these two organisms (DEMEREC and OHTA 1964) prompted us to initiate an analysis of the histidine region in E. coli so that it might be compared in detail to the one in Salmonella. Several aspects of this analysis were facilitated by the isolation in our laboratories of an F-merogenote or F’-episome (JACOB and ADELBERG 1959) in E. coli K12 that appeared to carry genetic information analogous to the histidine operon in Salmonella. Such a system makes possible (1 ) the construction of partially diploid derivatives that are heterozygous for specific his mutations and (2) the subsequent classification of the mutations into complementing groups. Since F-merogenotes are transmissible from E. coli to S. typhimurium it was possible to identify the enzyme defect involved in each complementation group in E. coli by introducing an F-merogenote carrying a specific his mutation into a set of S. typhimurium recipients with known defects and then noting the complementation pattern. In addition, the partially diploid system permitted the construction of E. coli heterogenotes carrying three his mutations and the ordering of the his mutations by three-factor analysis.