Comparison of regulatory and structural regions of genes of tryptophan metabolism.

The genes of tryptophan biosynthesis are arranged and regulated differently in many microorganisms. Comparison of the transcription regulatory regions of the trp operons of several species of enterobacteria reveals that those sequences and structures believed to be essential for repression and attenuation control are conserved. Examples of divergent and convergent evolutionary change are presented. Rearrangements involving the homologous trpG and pabA genes and their presumed ancestral bi-specific gene are described. Alignment of homologous sequences of trp polypeptides encoded by fused and nonfused genes from various species reveals short connecting amino acid sequences at fusion junctions. These connecting sequences may be relics of gene fusion events and/or they may facilitate the proper folding of neighboring polypeptide domains.