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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.

The eight Escherichia coli enzymes involved in the synthesis of histidine are encoded by the hisGDCBHAFI operon. Based on sequence data previously established, different restriction sites were deduced and used to map the position of the operon within the Kohara physical map. The results showed that the histidine operon is located around kb 2,100, corresponding to the 44-minute region.