The effects of leader peptide sequence and length on attenuation control of the trp operon of E.coli.

We have examined the effects of changing the length and codon content of the trp leader peptide coding region on expression of the trp operon of Escherichia coli, it had previously been shown that coupling of transcription and translation in the trp leader region is essential for both basal level control and tryptophan starvation control of transcription attenuation in this operon. We have found that increasing the length of the leader peptide coding region by 55 codons allowed normal basal level control and normal tryptophan starvation control. As expected, the presence of a nonsense codon early in the leader peptide coding region decreased basal expression and eliminated starvation control. Introducing tandem rare codons had no effect on basal level expression, but eliminated the tryptophan starvation response. Frameshifting at tandem rare codons was tested as the most likely explanation for loss of the tryptophan starvation response, but the results were inconclusive.