Uridine-sensitized screening identifies demethoxy-coenzyme Q and NUDT5 as regulators of nucleotide synthesis.

Rapidly proliferating cells require large amounts of nucleotides, making nucleotide metabolism a widely exploited therapeutic target against cancer, autoinflammatory disorders and viral infections. However, regulation of nucleotide metabolism remains incompletely understood. Here, we reveal regulators of de novo pyrimidine synthesis. Using uridine-sensitized CRISPR-Cas9 screening, we show that coenzyme Q (CoQ) is dispensable for pyrimidine synthesis, in the presence of the demethoxy-CoQ intermediate as alternative electron acceptor. We further report that the ADP-ribose pyrophosphatase NUDT5 directly binds PPAT, the rate-limiting enzyme in purine synthesis, which inhibits its activity and preserves the phosphoribosyl pyrophosphate (PRPP) pool. In the absence of NUDT5, hyperactive purine synthesis exhausts the PRPP pool at the expense of pyrimidine synthesis, which promotes resistance to purine and pyrimidine nucleobase analogues. Of note, the interaction between NUDT5 and PPAT is disrupted by PRPP, highlighting an intricate allosteric regulation. Overall, our findings reveal a fundamental mechanism of nucleotide balance and position NUDT5 as a regulator of nucleobase analogue metabolism.