Topology and functional domains of the yeast pore membrane protein Pom152p

Integral membrane proteins associated with the nuclear pore complex (NPC) are likely to play an important role in the biogenesis of this structure. Here we have examined the functional roles of domains of the yeast pore membrane protein Pom152p in establishing its topology and its interactions with other NPC proteins. The topology of Pom152p was evaluated by alkaline extraction, protease protection, and endoglycosidase H sensitivity assays. The results of these experiments suggest that Pom152p contains a single transmembrane segment with its N terminus (amino acid residues 1-175) extending into the nuclear pore and its C terminus (amino acid residues 196-1337) positioned in the lumen of the nuclear envelope. The functional role of these different domains was investigated in mutants that are dependent on Pom152p for viability. The requirement for Pom152p in strains containing mutations allelic to the NPC protein genes NIC96 and NUP59 could be alleviated by Pom152p's N terminus, independent of its integration into the membrane. However, complementation of a mutation in NUP170 required both the N terminus and the transmembrane segment. Furthermore, mutations in NUP188 were rescued only by full-length Pom152p, suggesting that the lumenal structures play an important role in the function of pore-side NPC structures.