Histidine biosynthetic pathway and genes: structure, regulation, and evolution

The histidine (his) biosynthetic pathway is the most studied biochemical pathway since the acceptance of the operon theory. The his pathway has been shown to be present from single cell forms to complex, multi-cell forms. The his genes have been cloned and sequenced in more than 20 species and have been shown to be controlled posttranscriptionally by a system of segmental stabilization of regions in the transcription code.