Tpr is a coiled-coil protein found near the nucleoplasmic side of the pore 
complex. Since neither the precise localization of Tpr nor its functions are 
well defined, we generated antibodies to three regions of Tpr to clarify these 
issues. Using light and EM immunolocalization, we determined that mammalian Tpr 
is concentrated within the nuclear basket of the pore complex in a distribution 
similar to Nup153 and Nup98. Antibody localization together with imaging of 
GFP-Tpr in living cells revealed that Tpr is in discrete foci inside the nucleus 
similar to several other nucleoporins but is not present in intranuclear 
filamentous networks (Zimowska et al., 1997) or in long filaments extending from 
the pore complex (Cordes et al., 1997) as proposed. Injection of anti-Tpr 
antibodies into mitotic cells resulted in depletion of Tpr from the nuclear 
envelope without loss of other pore complex basket proteins. Whereas nuclear 
import mediated by a basic amino acid signal was unaffected, nuclear export 
mediated by a leucine-rich signal was retarded significantly. Nuclear injection 
of anti-Tpr antibodies in interphase cells similarly yielded inhibition of 
protein export but not import. These results indicate that Tpr is a nucleoporin 
of the nuclear basket with a role in nuclear protein export.