Genetics: From Genes to Genomes

Termination of transcription finetunes regulation of trp operon.• trpR - mutants are not constitutive.• Repressor independent change in trp expression• Two alternative transcripts lead to differenttranscriptional outcomes.• Leader sequence can fold in two different stableconformations.• Tryptophan present – ribosome moves quickly past codons inleader allowing stem-loop to form terminating transcription• Tryptophan absent – ribosome stalls allowing normal stem loopstructure to form and transcription proceeds normallyCopyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display17-37