An operon is a functioning unit of key nucleotide sequences of DNA including an operator, a common promoter, and one or more structural genes, which is controlled as a unit to produce messenger RNA (mRNA), in the process of transcription by an RNA polymerase. History The term ‘‘operon’’ was first proposed in a short paper in the Proceedings of the French Academy of Science in 1960. From this paper, the so-called general theory of the operon was developed. This theory sug… (More on Operons)