Latex bead labelling and comparative immunofluorescence analysis of the p62 subunit of the TFIIH was performed as described previously [16,17] using primary mouse embryonic fibroblasts at passages 2–5. Two or more cell lines per genotype (except for the XpdTTD/†XP cells, in which only one cell line was used in repeated experiments) were used, and experiments were repeated 2–6 times per genotype.