Fig. 1

Genomic neighborhood of the trpA gene (a) and of the hisF gene (b) in five bacterial genomes. The neighborhoods were deduced from the BioCyc database [6] for the genomes of E. coli K-12, S. enterica enterica A3ES40, B. subtilis subtilis 168, Agrobacterium sp. H13–3, and A. thiooxydans ZJ. The output of BioCyc is shown schematically, but drawn to scale; neighboring genes not related to tryptophan or histidine biosynthesis are filled grey. The gene products of trpA and trpB and of hisH and hisF (all color-coded) form hetero-oligomers, respectively. The conservation of the trpA and trpB neighborhood in all five genomes suggests the formation of a TrpA/TrpB complex. For the same genomes, the neighborhood of the hisH gene would more likely propose a HisH/HisA/HisF, a HisH/HisA, or a HisA/HisF, but no HisH/HisF complex. Note that HisH and HisF form a hetero-dimer, whereas HisA is a monomeric protein [7]