AN NLS IS SUFFICIENT TO ENGAGE FACILITATED TRANSLOCATION BY THE NUCLEAR-PORE COMPLEX AND SUBSEQUENT INTRANUCLEAR BINDING

We investigated the nuclear transport of a fusion protein consisting o f a nuclear localization signal linked to P-galactosidase, normally a cytoplasmic protein. We microinjected the radiolabeled fusion protein into the cytoplasm of living Xenopus oocytes or supplied it directly t o the surface of the oil-isolated oocyte nucleus and measured its tran sport into the nucleus. Our data confirm that a nuclear localization s ignal is sufficient to entrain a protein's facilitated transport throu gh the nuclear pore complex and its subsequent nuclear accumulation. M oreover, nuclear envelope micropuncture experiments determine that the fusion protein's accumulation results from its intranuclear binding, demonstrating that no specific region of a transported protein - other than the nuclear localization signal itself - is required for facilit ated transport and intranuclear binding. Finally, we present evidence that the intranuclear binding of a transported protein requires not on ly its nuclear localization signal, but also its prior facilitated tra nsport through the nuclear pore complex. (C) 1994 Academic Press, Inc.