ACTB and cancer: In addition, we demonstrate that two cancer-associated mutations, arginine to glutamine at position 1467 (R1467Q) and glycine to arginine at position (G1484R), both of which are located on the opposite side of the CSB-WHD away from its ubiquitin-binding pocket, impair its ability to promote RNAPII occupancy at PPP sites of ACTB, GAPDH and RPL13A genes, providing the first evidence that CSB somatic mutations affect RNAPII association with PPP sites.