To investigate the possibility that ubiquitin modification is involved in the regulation of ERCC1 and XPF, we used western blotting to assess the response of both proteins from two human melanoma cell lines, A375 (from a metastatic melanoma) and C32 (from a primary melanoma), to proteasome inhibitor MG132 and translation inhibitor cycloheximide (Supplementary Figure 1). Here, ERCC4 is linked to metastatic melanoma.