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Homologous control sites and DNA transcription starts in the related argF and argI genes of Escherichia coli K12.

The argF and argI genes code for similar proteins able to assemble into hybrid isoenzymes and are therefore thought to share a common origin. We show here that the nucleotide sequence of the promoter and operator regions of these two genes are highly homologous. DNA regions preceding the control sites also present significant homologies. The results support the notion of divergent evolution of the two genes from a common ancestor. Like argE and argCBH, argF and argI are controlled by a repressor molecule recognizing a family of similar operator sites. Attenuation appears to play no role in this regulation.