Essential Genetics 6th Edition by Daniel Hartl

Exercise 13

You are studying a biochemical pathway in E. coli that leads to the production of substance A. You isolate a set of mutants, each of which is unable to grow on minimal medium unless it is supplemented with A. By performing appropriate matings, you group all the mutants into four complementation groups (genes) designated a1 , a2 , a3 , and a4. You know beforehand that the biochemical pathway for the production of A includes four intermediates: B, C, D, and E. You test the nutritional requirements of the mutants by growing them on minimal medium supplemented with each of these intermediates in turn. The results are summarized in the following table, where the plus signs indicate growth and the minus signs indicate failure to grow. Determine the order in which the substances A, B, C, D, and E are most likely to participate in the biochemical pathway, and indicate the enzymatic steps by arrows. Label each arrow with the name of the gene that codes for the corresponding enzyme.