POSSIBLE INVOLVEMENT OF A PERTUSSIS-TOXIN-SENSITIVE GTP-BINDING PROTEIN IN PROTEIN-TRANSPORT INTO NUCLEI ISOLATED FROM RAT-LIVER

Nuclear protein transport was inhibited in permeabilized HeLa cells wh ich had been prepared after culture with pertussis toxin, suggesting t hat the pertussis toxin-sensitive protein(s) might be involved in the nuclear protein transport. To investigate the mechanism whereby pertus sis toxin inhibited the nuclear protein transport, an accumulation of proteins containing a nuclear localization signal sequence (NLS) into isolated rat liver nuclei was investigated. The NLS-containing protein accumulation required ATP and cytosolic proteins, and was temperature - and wheat germ agglutinin-sensitive as had been observed in permeabi lized cells. Non-hydrolyzable GTP analogues, such as guanosine 5'-(gam ma-thio)triphosphate and guanosine 5'-(beta,gamma-methylene)triphospha te, but not ATP analogues, inhibited the NLS-containing protein accumu lation in the isolated nuclei. The NLS-containing protein accumulation was also inhibited by prior treatment of the nuclei with pertussis to xin plus NAD, and the effect of pertussis toxin was blocked when guano sine 5'-(gamma-thio)triphosphate was simultaneously added during the p retreatment with pertussis toxin. The inhibition induced by pertussin toxin and the blockage by guanosine 5'-(gamma-thio)triphosphate were w ell correlated to ADP-ribosylation of 40-kDa protein in nuclear fracti on. These results suggested that the nuclear pertussis toxin-sensitive GTP-binding protein is involved in a pathway of nuclear protein trans port.