ABSTRACT
The positioning of the ribosome prevents formation of the anti-terminator stem-loop but allows the terminator loop to form which then inhibits further transcription of the tryptophan operon (trp operon). The trp operon is regulated by both repression and attenuation. The function of the leader sequence is to fine tune expression of the trp operon based on the availability of tryptophan inside the cell. Historically, attenuation was discovered when it was noticed that deletion of a short sequence of Deoxyribonucleic acid between the operator and the first structural gene, trpe, increased the level of transcription. Overall, for the trp operon, repression via the trp repressor determines whether transcription will occur or not and attenuation then fine tunes transcription. Hence the availability of tryptophan controls whether transcription of this operon will stop early or continue to synthesize a complete polycistronic Messenger Ribonucleic acid.
