THE PEPTIDE REPEAT DOMAIN OF NUCLEOPORIN NUP98 FUNCTIONS AS A DOCKINGSITE IN TRANSPORT ACROSS THE NUCLEAR-PORE COMPLEX

We report the cDNA deduced primary structure of a wheat germ agglutini n-reactive nuclear pore complex (NPC) protein of rat. The protein, ter med Nup98 (for nucleoporin of 98 kDa), contains numerous GLFG and FG r epeats and some FXFG repeats and is thus a vertebrate member of a fami ly of GLFG nucleoporins that were previously discovered in yeast. Immu noelectron microscopy showed Nup98 to be asymmetrically located at the nucleoplasmic side of the NPC. Nup98 functions as one of several dock ing 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 r ecombinant segment of this region depleted the docking activity of cyt osol. We suggest that the peptide repeat domain of Nup98, together wit h peptide repeat domains of other nucleoporins, forms an array of site s for mediated docking of transport substrate, and that bidirectional transport across the NPC proceeds by repeated docking and undocking re actions.