Rho-dependent transcription termination in the tyrT operon of Escherichia coli

A 178-bp repeat sequence comprises the distal end of the tyrT operon and also encodes the signal for Rho-dependent transcription termination. It is shown here that Rho-dependent transcription termination is highly efficient for each of the individually cloned first and second repeats. The presence of either repeat results in a termination efficiency of 88% (12% readthrough). When an individual DNA repeat is shortened, starting from the promoter-proximal end, so that only 56 bp remain upstream from the termination site, Rho-dependent termination activity is reduced approximately three-fold (to give 38% readthrough) and with further shortening, so that only 15 bp remain upstream, Rho-dependent termination is reduced an additional 1.8-fold (to give 59% readthrough). Finally, it is shown that the presence or absence of the tyrT terminator upstream from the lambda tR1 terminator does not affect the efficiency of transcription at termination lambda tr1.