Gene Regulation in Prokaryotes

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Prokaryotic Gene Regulation:

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Gene Regulation in Prokaryotes An overview of expression in prokaryotes Regulation at the transcription level - Lactose operon (-ve induction), -ve regulation mutations of the lac operon - Positive control of lac operon, catabolite repression by glucose and role of CAP-cAMP - Structure of repressor prteins and nature of protein/DNA binding (helix-turn-helix HTH motifs) - Arabinose operon (+ve regulation) - How regulatory proteins, repressors or activators, interact with DNA elements and RNA polymerase - Applications of the lac operon in industry Regulation beyond the initiation of transcription involve fine-tuning of the amount of protein produced by attenuation - The Tryptophan operon

Overview of transcription in prokarotes: - RNA polymerase & steps of trasncription - Translation starts before transcription ends - mRNA is polycistronic

Regualtion at initiaition of transcription: - Lactose utilization - Lac operon - Mutations in the lac operon lac I- (muatnt repressor), constitutive lac Is (superrepressor) Oc (constitutive operator)

- Postive control of lac operon by CAP-cAMP or catabolite repression

Some catabolite operons have their own positive regulator such as the AraC protein of the arabinose operon. AraC is a homdimer. In the presence of arabinose, AraC acts as a positive regulator (induces transcription). In the absence of arabinose, AraC acts as a rerpressor

Repressor proteins have a helix-turn-helix HTH motif which binds to the major groove of the DNA double helix at the operator site of the operon. The technique of DNA footprinting identifies site on DNA that bind proteins. Regulatory proteins interact with RNA polymerase when both molecules are bound to DNA

Elements of the lactose operon have applications in biotechnology and industry: 1. The lacZ gene is used as a reporter in genetic engineering. 2. The promoter of the lactose operon is used in industry to drive the expression of important proteins e.g. human growth hormone.

Tryptophan operon: an example of regulation of anabolic pathways (pathways that lead to the synthesis of a building block such as an amino acid). Tryptophan acts as a corepressor Fine tuning of the operon occurs by attenuation, which is control of gene expression by premature termination of transcription