20. The following complementing E. coli mutants were tested for growth on four known
precursors of thymine, A-D.
Precursor/product
A B C D Thymine
Mutant
9
+
10
14
18
21
802
+
+
+
a. Show a simple linear biosynthetic pathway of the four precursors and the end
product, thymine. Indicate
which step is blocked by each of the five mutations.
b. What precursor would accumulate in the following double mutants: 9 and 10? 10
and 14?