Chapter 16, Problem 5P

The figure at the beginning of this chapter shows the binding of both a Lac repressor tetramer and a CRP-cAMP

complex to the regulatory region of the lac operon.

a.	What is the key feature of a regulatory protein such as the Lac repressor or CRP that allows it to regulate specifically the genes or operons it is supposed to control?
b.	On the figure, show the positions of the following components: (i) A Lac repressor monomer; (ii) a Lac repressor dimer; (iii) all four DNA binding domains of the Lac repressor tetramer; (iv) a single helix-turn helix motif; (v) the o part and either the o or o parts of the lac operator (assume the operon would be transcribed from right to left on the figure); (vi) the multimerization domains of the four Lac repressor monomers; (vii) an inducer-interacting domain; (viii) the CRP-cAMP complex; and (ix) a DNA loop.
c.	What is the physical basis for the formation of the DNA loop shown in the figure?
d.	On the figure, show the position of two axes of symmetry in the sequence of DNA. How do you know, only on the basis of the figure and without prior information about the precise DNA sequence, that these two axes of symmetry are likely to be present in the DNA and that the sequences around these axes are rotationally symmetrical?