Ms. Park et al., ULTRAVIOLET-INDUCED MOVEMENT OF THE HUMAN DNA-REPAIR PROTEIN, XERODERMA-PIGMENTOSUM TYPE-G, IN THE NUCLEUS, Proceedings of the National Academy of Sciences of the United Statesof America, 93(16), 1996, pp. 8368-8373
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.