What is an operon, and how does it regulate gene expression?
An operon is a segment of DNA that contains two or more genes that are transcribed as one messenger RNA (mRNA). The expression of all the genes in an operon is controlled by a single promoter (the upstream DNA sequence where RNA polymerase binds). The promoter of an operon is where the transcriptional regulation occurs. There are several mechanisms that can regulate the activity of a promoter- I’ll just discuss the most basic ones. First, in some bacteria, there are multiple different promoter sequences that can be recognized by RNA polymerase. The sequence that is recognized depends on the sigma subunit that is associated with the RNA polymerase core enzyme. So, expression can be regulated at that stage, depending on what form(s) of RNA polymerase are available at the time. Second, there are proteins called transcription factors that can regulate the activity of a promoter- usually by affecting how RNA polymerase works. There are two types- repressors can inhibit transcription, and ac
