An Activator Protein Is Discovered That Augments Operon Expression

An Activator Protein Is Discovered That Augments Operon Expression 

Although the genetic and biochemical studies on the action of repressor on the lac operon answered many questions about gene expression of the lac operon, they left equally important questions unanswered. It had been known since the turn of the century that the lac operon expresses at a 

The operator locus (the presumptive repressor binding site). Bases are numbered +1 for the first base transcribed and — 1 for the base before that. Regions showing dyad symmetry are underlined and overlined. Arrows indicate point mutations leading to the constitutive phenotype (oc). Circled bases are those groups that are strongly 

Beckwith and his colleagues isolated a large family of mutants that were permanently catabolite-repressed. These mutants fell into two categories Those that could be pheno-typically corrected by growing in the presence of cAMP and those that could not. The first class of mutants were believed to be defective in the synthesis of cAMP, and the latter class were presumed to be defective in the protein receptor for cAMP. Cell-free extracts were prepared from 

A series of genetic deletions was used to demonstrate that the site necessary for CAP stimulation of the lac operon is in the — 50-— 80 region of the lac operon. A 14-bp segment between —53 and —68 shows dyad symmetry for 12 of the 14 bp (fig. 30.8). 

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