MULTIPLE NUCLEAR-LOCALIZATION SIGNALS IN XPG NUCLEASE

We report here evidence for the mechanism of nuclear localization of X PG nuclease in human cells, Several candidate nuclear localization sig nal (NLS) peptides have been proposed for XPG protein. We have identif ied XPG peptides containing functional NLS and a potential nuclear ret ention signal (NRS) using in situ immune-fluorescence localization of transiently expressed beta-galactosidase fusion proteins. Two XPG regi ons with putative NLS [amino acid (AA) coordinates: NLS-B (AA 1057-107 4) and NLS-C (AA 1171-1185)] were each shown to independently localize the beta-gal extensively (> 80%) to the nucleus of HeLa cells. The C- terminus peptide containing NLS-C, all NLS conserved evolutionarily be tween yeasts and humans, also directed sub-localization of beta-galact osidase to intranuclear foci reminiscent of native XPG protein, as wel l as to peri-nucleolar regions. Peptides in the putative XPG 'NLS doma in' (AA similar to 1051-1185) apparently function in concert for nucle ar localization and also for retention of XPG in nuclear matrix-associ ated foci. Evidence presented elsewhere (Park et al., 1995) indicates that the peptide containing NLS-C (AA 1146-1185) also regulates the dy namic localization of XPG in the nucleus following UV-irradiation.