Histidine operon regulation

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. 

Several other operons for the biosynthesis of amino acids in E. coli also are regulated by attenuator sites. The leader peptide of each contains an abundance of the amino acid residues of the type synthesized by the operon (Figure 31.35). For example, the leader peptide for the phenylalanine operon includes 7 phenylalanine residues among 1 5 residues. The threonine operon encodes enzymes required for the synthesis of both threonine and isoleucine the leader peptide contains 8 threonine and 4 isoleucine residues in a 16-residue sequence. The leader peptide for the histidine operon includes 7 histidine residues in a row. In each case, low levels of the corresponding charged tRNA causes the ribosome to stall, trapping the na.scent mRNA in a state that can form a structure that allows RNA polymerase to read through the attenuator site. 

Regulation of the Histidine Operon Covalent Modification of Phosphofruc-... 

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