Figure 5-13. Regulation of lac operon in E. coli.

Figure 5-13Regulation of lac operon in E. coli

Structural genes lacZ, lacY, and lacA code for β-galactosidase, β-galactoside permease, and b-galactoside transacetylase, respectively. The physiologic role of lacA is unknown. The lac repressor is product of lacI gene in separate regulatory operon. Transcription of mRNA encoding lacZ, lacY, and lacA is negatively regulated. and binding of lac repressor to operator lacO prevents initiation of transcription at promoter lacP. Inducer binds to lac repressor and inactivates it. Catabolite activator protein (CAP) forms a complex with cyclic AMP, and binding of the complex to a site immediately adjacent to the lac promoter stimulates transcription of the lac operon by RNA polymerase. An expanded diagram of the lac operator-promoter region shows the binding sites for CAP, RNA polymerase, and lac repressor.

From: Chapter 5, Genetics

Cover of Medical Microbiology
Medical Microbiology. 4th edition.
Baron S, editor.
Copyright © 1996, The University of Texas Medical Branch at Galveston.

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