Evolution of a Biosynthetic Pathway: The Tryptophan Paradigm

Amplification of trpEG: adaptation of Buchnera aphidicola to an endosymbiotic association with aphids.

“…One ofthe most extensively studied biosynthetic pathways is that for the synthesis of tryptophan (19)(20)(21)(22). In almost all organisms, tryptophan biosynthesis is regulated by feedback inhibition of AS by tryptophan (23) and by repression of enzyme synthesis (20)(21)(22).…”

“…In almost all organisms, tryptophan biosynthesis is regulated by feedback inhibition of AS by tryptophan (23) and by repression of enzyme synthesis (20)(21)(22). In E. coli, tryptophan mediates the repression of an operon containing genes coding for all of the enzymes of tryptophan biosynthesis [trpEG(D)C(F)BA] (21).…”

“…In this and some other organisms, levels of tryptophan biosynthetic enzymes are also regulated by attenuation (transcription termination) based on the availability of charged tRNATrP (21,24,25). A property of this attenuation mechanism is the presence of DNA coding for a short tryptophancontaining leader peptide that precedes the structural genes for AS (20,21). Some species of Bacillus have a totally different mechanism of attenuation, which does not involve a leader peptide but does involve a tryptophan-dependent binding of a regulatory protein to trp mRNA (20,26).…”

“…A property of this attenuation mechanism is the presence of DNA coding for a short tryptophancontaining leader peptide that precedes the structural genes for AS (20,21). Some species of Bacillus have a totally different mechanism of attenuation, which does not involve a leader peptide but does involve a tryptophan-dependent binding of a regulatory protein to trp mRNA (20,26). All of these regulatory mechanisms, characteristic of free-living bacteria, respond to accumulation of tryptophan within the cell.…”

Crystallization and preliminary crystallographic studies of the anthranilate synthase partial complex fromSalmonella typhimurium

“…The TrpG domain represents the N-terminal 193 amino acids of ASII in S. typhimurium. The partial complex [(TrpE) 2 (TrpG) 2 ] is analogous to the complex that exists naturally in S. marcescens and numerous other bacteria (Crawford, 1989).…”