RanGTP mediates nuclear import and mitotic spindle assembly by dissociating 
import receptors from nuclear localization signal (NLS) bearing proteins. We 
investigated the interplay between import receptors and the transmembrane 
nucleoporin Pom121. We found that Pom121 interacts with importin alpha/beta and 
a group of nucleoporins in an NLS-dependent manner. In vivo, replacement of 
Pom121 with an NLS mutant version resulted in defective nuclear transport, 
induction of aberrant cytoplasmic membrane stacks and decreased cell viability. 
We propose that the NLS sites of Pom121 affect its function in NPC assembly both 
by influencing nucleoporin interactions and pore membrane structure.