Attenuation Tryptophan-starved: transcription not terminated Excess tryptophan: transcription terminated Leader sequence DNA Direction of Direction of transcription Translation stalled RNA 厂RNA Ribosome polymerase polymerase ontinue (terminates) Leader Tryptophan tructural Tryptophan peptide structural genes gene Trp-rich leader mRNA Direction of translation peptide Transcription terminated Figure 8.21Figure 8.21 Attenuation