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Modern Genetic Analysis Chapter 14. Regulation of Gene Transcription
Summary

The operon model explains how prokaryotic genes are controlled through a mechanism that coordinates the activity of a number of related genes. In negative control, the initiation of transcription is controlled at the operator by a repressor with binding affinities to the operator that may be altered by inducer molecules. Inactivation of the repressorthe negative control elementis required for active transcription. In positive control, transcription initiation requires the activation of a factor. Sometimes one control system is superimposed on another. For instance, superimposed on the repressoroperator system for the lac operon is the cAMPCAP positive control system.

A major problem in transcriptional control in eukaryotes is understanding how tens or hundreds of thousands of promoters can be regulated to yield desired levels of mRNA. It is now clear that promoters are governed both by the number and type of promoter-proximal and enhancer elements and by the action of regulatory proteins that recognize these elements. In some aspects, transcriptional control in eukaryotes is similar to that found in prokaryotes; namely, trans-acting factors recognize cis-acting sites in both cases. Layered on top of these similarities are differences imposed by the natures of unicellular versus multicellular life, such as the co-ordination of appropriate gene function in different tissues.

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