Functional Characterization of a Nup159p-containing Nuclear Pore Subcomplex

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Abstract
Nup159p/Rat7p is an essential FG repeat–containing nucleoporin localized at the cytoplasmic face of the nuclear pore complex (NPC) and involved in poly(A)+RNA export and NPC distribution. A detailed structural–functional analysis of this nucleoporin previously demonstrated that Nup159p is anchored within the NPC through its essential carboxyl-terminal domain. In this study, we demonstrate that Nup159p specifically interacts through this domain with both Nsp1p and Nup82p. Further analysis of the interactions within the Nup159p/Nsp1p/Nup82p subcomplex using the nup82Δ108mutant strain revealed that a deletion within the carboxyl-terminal domain of Nup82p prevents its interaction with Nsp1p but does not affect the interaction between Nup159p and Nsp1p. Moreover, immunofluorescence analysis demonstrated that Nup159p is delocalized from the NPC in nup82Δ108 cells grown at 37°C, a temperature at which the Nup82Δ108p mutant protein becomes degraded. This suggests that Nup82p may act as a docking site for a core complex composed of the repeat-containing nucleoporins Nup159p and Nsp1p. In vivo transport assays further revealed that nup82Δ108and nup159-1/rat7-1 mutant strains have little if any defect in nuclear protein import and protein export. Together our data suggest that the poly(A)+RNA export defect previously observed in nup82 mutant cells might be due to the loss from the NPCs of the repeat-containing nucleoporin Nup159p.