Characterization of a UV-damage recognition factor in vitro that is associated with UV resistance in HeLa cells

We have previously reported a cisplatin-selected HeLa cell line showing cross-resistance to ultraviolet (UV) radiation and overexpression of UV-damage recognition factors (Chao et al., Mol. Cell. Biol., 11, 2075-2080, 1991). Here, we further characterize a UV-damage recognition factor in vitro using a gel mobility shift assay. The results indicate that the damage-recognition factor is (i) localized mostly in the nucleus, (ii) protease-sensitive, (iii) RNA-independent, (iv) active in a wide range of ionic strengths (50-400 mM NaCl), (v) with a high affinity for UV-damaged DNA (50-fold molar excess competitor causes 50% recognition loss), and (vi) resistant to agents and that modify protein conformation (urea and NP-40), but slightly sensitive to CaCl2. The significance of the identified UV-damage recognition factor in the sensitivity or resistance of cells to UV is also discussed.