In human tumor cells, Cdk1 promoted the phosphorylation of ribose-phosphate diphosphokinase 1 (PRPS1) at S103, and the loss of phosphorylation at S103 altered the cell cycle, which was similar to the alteration of the cell cycle observed in ΔBbTdp1 mutants (33). This evidence concerns the gene PRPS1 and neoplasm.