1. Gene regulation in prokaryotes March 27, 2006

2. Inducible transcription: lac operon

4. Transcription termination by attenuation: trp operon

5. Transcription termination by attenuation Two possible base- pairing schemes within the mRNA at the beginning of the trp operon

6. Transcription termination by attenuation Not enough tryptophan amino acids causes ribosome to stall on the mRNA  allows pre- emptor stemloop to form  termination does not occur Moving ribosome  pre-emptor structure does not form – terminator stemloop forms – terminates transcription of the rest of the mRNA

7. Regulation in phage lambda( )