The membrane-spanning glycoprotein gp210 is a major component of the nuclear 
pore complex. This nucleoporin contains a large cisternal N-terminal domain, a 
short C-terminal cytoplasmic tail, and a single transmembrane segment. We show 
here that dimers of native gp210 can be isolated from cell extracts by 
immunoprecipitation, and from purified rat liver nuclear envelopes by velocity 
sedimentation and gel filtration. Cross-linking of proteins in isolated 
membranes prior to solubilization dramatically increases the proportion of 
dimers. The dimers are SDS-resistant, as previously observed for some integral 
membrane proteins of cis-Golgi and plasma membrane proteins, including 
glycophorin A. Larger oligomers of gp210 can also be obtained by gel filtration 
and denaturing electrophoresis, but unlike the dimers are dissociated by 
reduction and heating in the presence of SDS. We propose that gp210 is organized 
into the pore membrane as a large array of gp210 dimers that may constitute a 
luminal submembranous protein skeleton.