Polκ κ κ κ is one of many DNA polymerases involved in translesion DNA synthesis (TLS). It belongs to the Y-family of polymerases along with Polη η η η, Polι ι ι ι and hREV1. Unlike Polη η η η encoded by the xeroderma pigmentosum variant (XPV ) gene, Polκ κ κ κ is unable to bypass UV-induced DNA damage in vitro, but it is able to bypass benzo[a]pyrene (B[a]P)-adducted guanines accurately and efficiently. In an attempt to identify factor(s) targeting Polκ κ κ κ to its cognate DNA lesion(s), we searched for Polκ κ κ κ-interacting proteins by using the yeast two-hybrid assay. We found that Polκ κ κ κ interacts with a C-terminal region of hREV1. Polη η η η and Polι ι ι ι were also found to interact with the same region of hREV1. The interaction between Polκ κ κ κ and hREV1 was confirmed by pull-down and coimmunoprecipitation assays. The C-terminal region of hREV1 is known to interact with hREV7, a non-catalytic subunit of Polζ ζ ζ ζ that is another structurally unrelated TLS enzyme, and we show that Polκ κ κ κ and hREV7 bind to the same C-terminal region of hREV1. Thus, our results suggest that hREV1 plays a pivotal role in the multi-enzyme, multi-step process of translesion DNA synthesis.

For mammalian nucleotide excision repair (NER), DNA lesions are recognized in at least two steps involving detection of unpaired bases by the XPC protein complex and the subsequent verification of injured bases. Although lesion verification is important to ensure high damage discrimination and the accuracy of the repair system, it has been unclear how this is accomplished. Here, we show that damage verification involves scanning of a DNA strand from the site where XPC is initially bound. Translocation by the NER machinery exhibits a 5'-to-3' directionality, strongly suggesting involvement of the XPD helicase, a component of TFIIH. Furthermore, the initial orientation of XPC binding is crucial in that only one DNA strand is selected to search for the presence of lesions. Our results dissect the intricate molecular mechanism of NER and provide insights into a strategy for mammalian cells to survey large genomes to detect DNA damage.

In this study, we aimed to evaluate changes in the acute toxicity of intraperitoneally administered silver nanoparticles (AgNPs) of varying sizes in BALB/c mice. Seven-week-old female BALB/c mice were intraperitoneally administered AgNPs measuring 10, 60, or 100 nm in diameter (0.2 mg/mouse) and then sacrificed 1, 3, or 6 h after treatment. In mice administered 10 nm AgNPs, reduced activity and piloerection were observed at 5 h post administration, and lowered body temperature was observed at 6 h post administration, with histopathological changes of congestion, vacuolation, single cell necrosis, and focal necrosis in the liver; congestion in the spleen; and apoptosis in the thymus cortex. These histopathological changes were not evident following administration of either 60 or 100 nm AgNPs. These results suggested that smaller AgNPs, e.g., those measuring 10 nm in diameter, had higher acute toxicity in mice.

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