noun, plural: operons
A group of genes or a segment of DNA that functions as a single transcription unit. It is comprised of an operator, a promoter, and one or more structural genes that are transcribed into one polycistronic mRNA.
The operon acts as a unit of transcription, and functions in a coordinated manner to produce by transcription a single mRNA molecule which codes for more than one protein with related metabolic functions. The first described operon is the lac operon.