The Prader-Willi syndrome (PWS) region in 15q11q13 harbours a cluster of 
imprinted genes expressed from the paternal chromosome only. Whereas loss of 
function of the SNORD116 genes appears to be responsible for the major features 
of PWS, the role of the other genes is less clear. One of these genes is 
C15orf2, which has no orthologues in rodents, but appears to be under strong 
positive selection in primates. C15orf2 encodes a 1156 amino acid protein with 
six nuclear localisation sequences. By protein BLAST analysis and InterProScan 
signature recognition search, we found sequence similarity of C15orf2 to the 
nuclear pore complex (NPC) protein POM121. To determine whether C15orf2 is 
located at nuclear pores, we generated a stable cell line that inducibly 
expresses FLAG-tagged C15orf2 and performed immunocytochemical studies. We found 
that C15orf2 is present at the nuclear periphery, where it colocalizes with NPCs 
and nuclear lamins. At very high expression levels, we observed invaginations of 
the nuclear envelope. Extending these observations to three-dimensional 
structured illumination microscopy, which achieves an 8-fold improved volumetric 
resolution over conventional imaging, we saw that C15orf2 is located at the 
inner face of the nuclear envelope where it strongly associates with the NPC. In 
nuclear envelope isolation and fractionation experiments, we detected C15orf2 in 
the NPC and lamina fractions. These experiments for the first time demonstrate 
that C15orf2 is part of the NPC or its associated molecular networks. Based on 
our findings, we propose 'Nuclear pore associated protein 1' as the new name for 
C15orf2.