Histidine operon genes, mapping

Regulation of histidine synthesis. In all, ten different genes code for the enzymes of histidine biosynthesis in Salmonella typhimurium. They are clustered as the histidine operon, a consecutive series of genes which are transcribed into messenger RNA as a unit.250 251 The gene symbols His A, HisB, etc., are indicated in Fig. 25-13, and their positions on the E. coli gene map are indicated in Fig. 26-4. The gene HisB codes for a complex protein with two different enzymatic activities as shown in Fig. 25-13. 

The histidine genes of S. typhimurium are among the best-characterized operons. The structural genes for the enz5mies of the histidine operon (ten enzymes that convert the 5-carbon chain of phosphoribosyl pyrophosphate to histidine) are in a cluster on the Salmonella chromosome. More than a thousand histidine-requiring mutants have been located on a fine-structure map of the operon (Whitfield et al. 1966). 

A. Mapping of the Histidine Enzyme Genes—Discovery of the Operon 360... 

The study of orientation of the histidine operon on the genetic map of S. typhimurium (Hartmann et al., 1965) showed that if this operon is located on the bacterial chromosome, it lies in a clockwise direction between the following genes (operons) gal—try - 1-HisO-G-D-C B- H A-F I-E-metG-purG-str-metA. 

Fig, 26, General map of the histidine operon from data of Ames and Hartmann and collaborators (Ames, 1965), Capital letters between diagrams refer to gene loci. 

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