Four Different Uracil Auxotrophs of Neurospora, a Eukaryotic Mold, Are $\quad\quad\quad\quad\quad\quad\quad { \text { Compound } }$

Four different uracil auxotrophs of Neurospora, a eukaryotic mold, are tested for growth on uracil and uracil precursors. The data are shown in the following table. A plus sign (+) means growth. $\quad\quad\quad\quad\quad\quad\quad { \text { Compound } }$

$\begin{array} { | l | l | l | l | l | l } \hline & \text { A } & \text { B } & \text { C } & \text { D } & \text { Uracil } \\\hline \text { Mutant 1 } & + & + & + & - & + \\\hline \text { Mutant 2 } & - & - & + & - & + \\\text { Mutant 3 } & + & - & + & - & + \\\text { Mutant 4 } & - & - & - & - & + \\\hline\end{array}$
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Diagram the uracil pathway, showing the step at which each mutant is blocked.