Brandl lecture 2 regulation of gene expression. Found in bacteria but not in eukaryotes conserved for bacteria. Gene specific regulatory proteins dynamic: negative regulation factors repress transcription trp operon and trp repressor, positive regulation factors activate transcription eukaryotic reduction system. Trp operon in e. coli the 5 genes (e, d, b, c, a) for tryptophan biosynthesis are transcribed from a common promoter. Five proteins are required for tryptophan biosynthesis enzymes are made from this. Trp operon is regulated by concentration of trp in the environment/medium: trp production is induced when there is little trp in the environment. A: when there is little tryptophan in cellular environment. Trp promoter typical with +1 start site and -35 and -10. The trp repressor-trp complex blocks rna polymerase from the promoter so that no transcription is possible allosterically inhibits transcription. The trp repressor no longer binds to the operator. When *trp+ is low, trp dissociates from trp repressor.