We report that the expression of murine or human mutant p53 proteins in cells with no endogenous p53 proteins confers new or additional phenotypes upon these cells. Mutant p53 proteins expressed in cell lines lacking p53 resulted in either enhanced tumorigenic potential in nude mice ((10)3 cells) or enhanced plating efficiency in agar cell culture (human SAOS-2 cells). Also, mutant human p53 alleles, unlike the wild-type p53 protein, could also enhance the expression of a test gene regulated by the multi-drug resistance enhancer-promoter element. These data demonstrate a gain of function associated with p53 mutations in addition to the loss of function shown previously to be associated with mutations in this tumour suppressor gene.

Two cytosolic fractions (A and B) from Xenopus oocytes are sufficient to support protein import into the nuclei of digitonin-permeabilized cells. Fraction A recognizes the nuclear localization sequence (NLS) and binds the import substrate to the nuclear envelope, whereas fraction B mediates the subsequent passage of the bound substrate into the nucleus. Here we report that two interacting components are required for full fraction-B activity, purify one of these components to homogeneity, and show that it is the highly abundant GTP-binding protein Ran (Ras-related nuclear protein)/TC4.

We report the cDNA deduced primary structure of a wheat germ agglutinin-reactive nuclear pore complex (NPC) protein of rat. The protein, termed Nup98 (for nucleoporin of 98 kDa), contains numerous GLFG and FG repeats and some FXFG repeats and is thus a vertebrate member of a family of GLFG nucleoporins that were previously discovered in yeast. Immunoelectron microscopy showed Nup98 to be asymmetrically located at the nucleoplasmic side of the NPC. Nup98 functions as one of several docking site nucleoporins in a cytosolic docking activity-mediated binding of a model transport substrate. The docking site of Nup98 was mapped to its N-terminal half, which contains all of the peptide repeats. A recombinant segment of this region depleted the docking activity of cytosol. We suggest that the peptide repeat domain of Nup98, together with peptide repeat domains of other nucleoporins, forms an array of sites for mediated docking of transport substrate, and that bidirectional transport across the NPC proceeds by repeated docking and undocking reactions.