RNA undergoing nuclear export first encounters the basket of the nuclear pore. 
Two basket proteins, Nup98 and Nup153, are essential for mRNA export, but their 
molecular partners within the pore are largely unknown. Because the mechanism of 
RNA export will be in question as long as significant vertebrate pore proteins 
remain undiscovered, we set out to find their partners. Fragments of Nup98 and 
Nup153 were used for pulldown experiments from Xenopus egg extracts, which 
contain abundant disassembled nuclear pores. Strikingly, Nup98 and Nup153 each 
bound the same four large proteins. Purification and sequence analysis revealed 
that two are the known vertebrate nucleoporins, Nup96 and Nup107, whereas two 
mapped to ORFs of unknown function. The genes encoding the novel proteins were 
cloned, and antibodies were produced. Immunofluorescence reveals them to be new 
nucleoporins, designated Nup160 and Nup133, which are accessible on the basket 
side of the pore. Nucleoporins Nup160, Nup133, Nup107, and Nup96 exist as a 
complex in Xenopus egg extracts and in assembled pores, now termed the Nup160 
complex. Sec13 is prominent in Nup98 and Nup153 pulldowns, and we find it to be 
a member of the Nup160 complex. We have mapped the sites that are required for 
binding the Nup160 subcomplex, and have found that in Nup98, the binding site is 
used to tether Nup98 to the nucleus; in Nup153, the binding site targets Nup153 
to the nuclear pore. With transfection and in vivo transport assays, we find 
that specific Nup160 and Nup133 fragments block poly[A]+ RNA export, but not 
protein import or export. These results demonstrate that two novel vertebrate 
nucleoporins, Nup160 and Nup133, not only interact with Nup98 and Nup153, but 
themselves play a role in mRNA export.