The complex of RAD18, an E3 ubiquitin ligase, and UBE2B (RAD6), an E2 ubiquitin conjugating enzyme, monoubiquitinates PCNA associated with damaged DNA on lysine residue K164, using the ubiquitin residue K63 to create the covalent bond (Hoege et al. 2002). The catalytic subunit of DNA polymerase delta (POLD), POLD1
, does not bind monoubiquitinated PCNA (Park et al. 2014), implying that replicative polymerases POLD and POLE (DNA polymerase epsilon complex) dissociate from PCNA monubiquitinated at K164. This is in accordance with the proposed DNA polymerase switch during translesion DNA synthesis (TLS) (Friedberg et al. 2005). DNA damage induced removal of PCNA-associated protein KIAA0101 (PAF15) through proteasome-mediated degradation facilitates switching from replicative DNA polymerases POLD and POLE to TLS polymerases (Povlsen et al. 2012).
The ubiquitin ligase complex RBX1:CUL4:DDB1:DTL can also monoubiquitinate PCNA. RBX1:CUL4:DDB1:DTL is probably responsible for the basal monoubiquitination of PCNA and may contribute to the kinetics of DNA-damage induced PCNA monoubiquitination (Terai et al. 2010).