Intranuclear location of the adenovirus type 5 E1B 55-kilodalton protein

The intracellular location of the adenovirus type 5 E1B 55-kilodalton (kDa) protein, particularly the question of whether it is associated with nuclear pore complexes, was examined. Fractionation of adenovirus type 5-infected HeLa cell nuclei by an ablished procedure (N. Dwyer and G. Blobel, J. Cell. Biol. 70: 581-591, 1976) yielded one population of E1B 55-kDa protein molecules released by digestion of nuclei with RNase A and a second poulation recovered in the pore complex-lamina fraction. Free and E1B 55-kDa protein-bound forms of the E3 34-kDa protein (P. Sarnow, C.A. Sullivan, and A.J. Levine, Virology 120: 387-394, 1982) were largely recovered in the pore complex-lamina fraction. Nevertheless, the association of E1B 55-kDa protein molecules with this nuclear envelope fraction did not depend on interaction of the E1B 55-kDa protein with the E4 34-kDa protein. Comparison of the immunofluorescence patterns observed with antibodies recognizing the E1B 55-kDa protein or cellular pore complex proteins and of the behavior of these viral and cellular proteins during in situ fractionation suggests that the E1B 55-kDa protein does not become intimately or stably associated with pore complexes in adenovirus-infected cells.