Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 1

As you look at Figure 14.10, discuss possible "molecular ways" that the cAMP-CAP complex and lac repressor may influence RNA polymerase function. In other words, try to explain how the bending and looping in DNA may affect the ability of RNA polymerase to initiate transcription.FIGURE 14.10 The binding of the lac repressor to two operator sites. (a) The binding of the lac repressor protein to the O1 and O3 or to the O1 and O2 operator sites. Because the two sites are far apart, a loop must form in the DNA. (b) A molecular model for the binding of the lac repressor to O1 and O3. Each repressor dimer binds to one operator site, so the repressor tetramer brings the two operator sites together. This causes the formation of a DNA loop in the intervening region. Note that the DNA loop contains the 35 and 10 regions (shown in green), which are recognized by factor of RNA polymerase. This loop also contains the binding site for the cAMP-CAP complex, which is the blue protein within the loop.