Gene organisation of archaeal and bacterial trp gene clusters. Each panel A – F represents the occurrence and orientation of trp genes in the genomes of organisms listed in the second column. The third column gives the species-type and the taxonomical lineage. "E" marks Euryarchaeota, "C" Crenarchaeota, and "B" bacteria. A vertical double line (Panels A and D) indicates borders of gene clusters separately located in the genome. Open arrows represent hypothetical genes. The arrows are not to scale; gaps of arbitrary length were inserted between genes to allow the alignment of arrows. For acronyms of species-types, see legend of Table 2.