PCNA and cancer: Despite the general agreement between the UNG depletion and inhibition results in cell lines, the fact that UNG uses its 90–amino acid noncatalytic N-terminal domain (NTD) to interact with replication protein A (RPA) and proliferating cell nuclear antigen (PCNA), raises the possibility that loss of the protein-protein interactions in the depletion approach could be more detrimental to cancer cell growth than inhibition alone in some contexts, including in vivo studies (11–16).