Determination of trpL mRNA stem loop

(a) In tryptophan abundance, the 3–4 (termination) stem loop terminates transcription after the poly-U string. (b) In tryptophan starvation, the 2–3 (antitermination) stem loop leads to polycistronic mRNA synthesis(a) In tryptophan abundance, the 3–4 (termination) stem loop terminates transcription after the poly-U string. (b) In tryptophan starvation, the 2–3 (antitermination) stem loop leads to polycistronic mRNA synthesis

(a) Tryptophan abundance: Termination ‘uunununnt—nth Region 4 Ribosome completes translation of trpL coding sequence and occupies regions 1 and 2. Regions 3 and 4 pair, and transcription terminates. (b) Tryptophan starvation: Antitermination Region 4 W‘""“"~"HGA 4* “‘1"V‘lI/Hv‘yvfldqflfiiiilllllIItIICIIII—ttal“ Ribosome stalls at region 1, and regions 2 and 3 pair. Transcription continues into operon l l polypeptide region