Transcript secondary structures regulate transcription termination at the attenuator of S. marcescens tryptophan operon.

We have analysed the regulatory behaviour of deletion mutants lacking different segments of the leader region of the tryptophan operon of Serratia marcescens. Our results support the model in which a particular RNA structure, the terminator, is recognized during transcription as a transcription termination signal, and an alternative RNA structure, the anti-terminator, prevents formation of the terminator. It appears that the role of translation, ribosome stalling and shifts between alternative RNA secondary structures, is simply to regulate formation of the terminator.