PRPS1 and acute lymphoblastic leukemia: This is due to an eIF-4E cis-regulatory pyrimidine-rich translational element (PRTE) found in mPRPS2 and hPRPS2 [52,195], but not in the corresponding PRPS1 genes, which renders PRSP2 resistant to feedback inhibition by ADP and GDP and may also explain the therapy-resistant human cell lines associated with ALL [190].