 CRL4s also utilize Cdt2 and PCNA to degrade the p12 subunit of DNA polymerase δ during S phase and after UV irradiation.CRL4A complexes appear to induce the degradation of numerous members of the HOX transcription family, which are essential regulators of haematopoiesis.The first member of the HOX family identified as a target of CRL4A-mediated degradation is HOXA9, which is essential for haematopoietic stem cell maintenance and has been implicated in a subset of myeloid leukemias.