Gene order in the trp operon corresponds to reaction order in the biosynthetic pathway

The chromosomal order of genes in the trp operon of E. coli and the sequence of reactions catalyzed by the enzyme products of the trp structural genes. The products of genes trpD and trpE form a complex that catalyzes specific steps, as do the products of genes trpB and trpA. Tryptophan synthetase is a tetrameric enzyme formed by the products of trpB and trpA. It catalyzes a two-step process leading to the formation of tryptophan. Abbreviations: PRPP, phosphoribosylpyrophosphate; CDRP, 1-(o-carboxyphenylamino)-1-deoxyribulose 5-phosphate.

[Data from S. Tanemura and R. H. Bauerle, Genetics 95, 1980, 545]