Tryptophan operon leader

The Tryptophan operon leader is an RNA element found at the 5' of some bacterial tryptophan operons. The leader sequence can assume two different secondary structures known as the terminator and the anti-terminator structure. The leader also codes for very short peptide sequence that is rich in Tryptophan. The terminator structure is recognised as a termination signal for RNA polymerase and the operon is not transcribed. This structure forms when the cell has an excess of tryptophan and ribosome movement over the leader transcript is not impeded. When there is a deficiency of the charged tryptophanyl tRNA the ribosome translating the leader peptide stalls and the antiterminator structure can form. This allows RNA polymerase to transcribe the operon.

At least 6 different amino acid operons are known to be regulated by this attenuation.