ULTRAVIOLET-INDUCED MOVEMENT OF THE HUMAN DNA-REPAIR PROTEIN, XERODERMA-PIGMENTOSUM TYPE-G, IN THE NUCLEUS

Xeroderma pigmentosum type G (XPG) is a human genetic disease exhibiti ng extreme sensitivity to sunlight, XPG patients are defective XPG end onuclease, which is an enzyme essential for DNA repair of the major ki nds of solar ultraviolet (UV)-induced DNA damages. Here we describe a novel dynamics of this protein within the cell nucleus after UV irradi ation of human cells. Using confocal micropscopy, we have localized ti le immumofluorescent, antigenic signal of XPG protein to foci througho ut the cell nucleus, Our biochemical studies also established that XPG protein forms a tight association with nuclear structure(s). In human skin fibroblast cells, the number of XPG foci decreased within 2 h af ter UV irradiation, whereas total nuclear XPG fluorescence intensity r emained constant, suggesting redistribution of XPG from a limited numb er of nuclear foci to the nucleus overall. Within 8 h after UV, most X PG antigenic signal was found as foci, Using beta-galactosidase-XPG fu sion constructs (beta-gal-XPG) transfected into HeLa cells, we have id entified a single region of XPG that is evidently responsible both for foci formation and for the UV dynamic response. The fusion protein ca rrying the C terminus of XPG (amino acids 1146-1185) localized beta-ga l specific antigenic signal to foci and to the nucleolus regions, Afte r UV irradiation, antigenic beta-gal translocated reversibly from the subnuclear structures to the whale nucleus with kinetics very similar to the movements of XPG protein, These findings lead us to propose a m odel in which distribution of XPG protein may regulate the rate of DNA repair within transcriptionally active and inactive compartments of t he cell nucleus.