The nuclear pore complex is the predominant structure in the nuclear envelope 
that spans the double nuclear membranes of all eukaryotes. Yeasts have one 
additional organelle that is also embedded in the nuclear envelope: the spindle 
pole body, which functions as the microtubule organizing center. The only 
protein known to localize to and be important in the assembly of both of these 
yeast structures is the integral membrane protein, Ndc1p. However, no homologues 
of Ndc1p had been characterized in metazoa. Here, we identify and analyze NDC1 
homologues that are conserved throughout evolution. We show that the overall 
topology of these homologues is conserved. Each contains six transmembrane 
segments in its N-terminal half and has a large soluble C-terminal half of 
approximately 300 amino acids. Charge distribution analysis infers that the N- 
and C-termini are exposed to the cytoplasm. Limited proteolysis of yeast Ndc1p 
in cellular membranes confirms the orientation of its C-terminus. Although it is 
not known whether vertebrate NDC1 protein localizes to nuclear pores like its 
yeast counterpart, the human homologue contains three FG repeats in the 
C-terminus, a feature of many nuclear pore proteins. Moreover, a small region 
containing mutations that affect assembly of the nuclear pore in yeast is highly 
conserved throughout evolution. Lastly, we bring together data from another 
study to demonstrate that the human homologue of NDC1 is the known inner nuclear 
membrane protein, NET3.