Chapter 16, Problem 19P

Cells containing missense mutations in the crp gene (encoding the positive regulator CRP) are Lac^-, Mal^-, Gal^-, etc. To find cells with suppressors of the crp mutation (that is, cells with the crp mutation that behave as if they are crp^+>), cells were screened to find those that were both Lac⁺ and Mal⁺.

a. What types of suppressor mutations would you expect to obtain using this screen compared with a screen for Lac+ only?

b. All suppressors isolated were mutant in the gene for the α-subunit of RNA polymerase. What hypothesis could you propose based on this analysis?