When a replicative
DNA polymerase stalls upon encountering a photoproduct on the template strand, it is relieved by other low-processivity polymerase(s), which insert
nucleotide(s) opposite the lesion. Using an alkaline
sucrose density gradient sedimentation technique, we previously classified this process termed UV-induced translesion replication (UV-TLS) into two types. In human
cancer cells or
xeroderma pigmentosum variant (XP-V) cells, UV-TLS was inhibited by
caffeine or
proteasome inhibitors. However, in normal human cells, the process was insensitive to these
reagents. Reportedly, in yeast or mammalian cells, REV3
protein (a catalytic subunit of
DNA polymerase ζ) is predominantly involved in the former type of TLS. Here, we studied UV-TLS in fibroblasts derived from the Rev3-knockout mouse embryo (Rev3KO-MEF). In the wild-type MEF, UV-TLS was slow (similar to that of human
cancer cells or XP-V cells), and was abolished by
caffeine or
MG-262. In 2 cell lines of Rev3KO-MEF (Rev3(-/-)p53(-/-)), UV-TLS was not observed. In p53KO-MEF, which is a strict control for Rev3KO-MEF, the UV-TLS response was similar to that of the wild-type. Introduction of the Rev3 expression plasmid into Rev3KO-MEF restored the UV-TLS response in selected stable transformants. In some transformants, viability to UV was the same as that in the wild-type, and the death rate was increased by
caffeine. Our findings indicate that REV3 is predominantly involved in UV-TLS in mouse cells, and that the REV3 translesion pathway is suppressed by
caffeine or
proteasome inhibitors.