**4.1.5 Representation of NER activity by HCR assay**

Since the pCMV-Luc is damaged by UV, the DNA repair activity (responsible to UV) can be represented as the *Renilla*–calibrated firefly luciferase activity derived from UV-damaged pCMV-Luc verse to those from undamaged pCMV-Luc. By this way, one can compare the effects of various environmental toxicants on cellular DNA repair capacity. For example, an inhibitory effect of arecoline on the repair of UV-damaged pCMV-Luc can be found by using HCR assay (Fig. 1C).

Fig. 1. Schematic illustration of host cell reactivation (HCR) assay for examination of nucleotide excision repair.

(A) The reporter plasmid pCMV-Luc is prepared in *E. coli*.

(B) The pCMV-Luc is damaged by 1000 J/m2 of UV light.

(C) Comparison of the effects of arecoline (ARE, 0.3 mM) and its vehicle (distilled water) on the repair of UV-damaged pCMV-Luc in HEp-2 cells.
