Regulator Genes

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Regulation of Protein Synthesis - Operon Structural Genes Operator Genes Promoter Gene Regulator Gene Control Mechanism - Induction Control Mechanism - Repression Inducible System Repressible System Negative Control of Protein Synthesis Positive Control of Protein Synthesis Mutation in the Operon

Regulator Genes

	Regulator Genes - The regulator gene directs the synthesis of a protein, which may be an active repressor or an inactive repressor (aporepressor). In the inducible system the active repressor formed has an affinity for the operator gene. In the absence of an inducer the lac repressor protein binds to the operator gene and blocks the path of RNA polymerase. Thus the structural genes are unable to transcribe mRNA, and protein synthesis does not take place. In the presence of all inducer, (e.g. lactose) the repressor protein binds to the inducer to form an inducer repressor complex.
Each repressor subunit has one binding site for the inducer. The repressor undergoes a conformational change which makes it inactive. It cannot now bind to the operator gene, and hence the structural genes can synthesize proteins. In the repressible system the repressor protein formed by the regulator gene is inactive and does not block the operator. The structural genes, therefore synthesize proteins. The repressor is activated in the presence of a corepressor, and the repressor corepressor complex blocks the operator gene. The structural genes, therefore, cannot synthesize proteins.
In the lac operon of E.coli the repressor protein produced by the regulator gene consists of four subunits, each of 40,000 daltons, and has 347 amino acid residues. The active repressor protein has a strong affinity for a segment of the operator gene composed of 12-15 nucleotides.

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Regulation of Gene Activity in Eukaryotes Frenster's Model of Gene Regulation Nonhistone Protein as Derepressors Britten Davidson Operon Operator Model Sensor Genes Producer Genes Integrator Genes Receptor Genes