Isolation and sequence analysis of the trpBA gene cluster, encoding tryptophan synthase, from Azospirillum brasilense

The trpBA gene cluster of Azospirillum brasilense Sp7 was isolated by compl ementation of an Escherichia coli trpBA mutant. Both genes code for the two subunits of tryptophan synthase, which catalyzes the last step in tryptoph an biosynthesis. No structural features indicating transcriptional regulati on could be identified. Upstream of the trpBA cluster an open reading frame encoding a putative periplasmic binding protein, involved in amino acid tr ansport, was identified. Analysis of the downstream region of the trpBA clu ster revealed the presence of a putative open reading frame encoding a subu nit of the acetyl-coenzyme A carboxylase carboxyl transferase complex.