It is a (positive, negative) (repressible, inducible) operon. Therefore, when tryptophan is low the operon is (on, off) and when tryptophan is high the operon is (on, off). One of the main mechanisms of control for this operon is attenuation, which depends on simultaneous _____________________ and __________________. Which secondary structure promotes attenuation? ________________________ Which secondary structure allows transcription to continue? _______________ When tryptophan levels are low, the ribosome stalls at region _____, leaving region _____ and region _____ uncovered so they can pair and transcription can continue. Why does the ribosome stall?