Functional characterization of a Nup159p-containing nuclear pore subcomplex

Nup159p/Rat7p is an essential FG repeat-containing nucleoporin localized at the cytoplasmic face of the nuclear pore complex (NPC) and involved in pol y(A)(+) RNA export and NPC distribution. A detailed structural-functional a nalysis of this nucleoporin previously demonstrated that Nup159p is anchore d within the NPC through its essential carboxyl-terminal domain. In this st udy, we demonstrate that Nup159p specifically interacts through this domain with both Nsp1p and Nup82p. Further analysis of the interactions within th e Nup159p/Nsp1p/Nup82p subcomplex using the nup82 Delta 108 mutant strain r evealed that a deletion within the carboxyl-terminal domain of Nup82p preve nts 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 nup82 Delta 108 cells grown at 37 de grees C, a temperature at which the Nup82 Delta 108p mutant protein becomes degraded. This suggests that Nup82p may act as a docking site for a core c omplex composed of the repeat-containing nucleoporins Nup159p and Nsp1p. In vivo transport assays further revealed that nup82 Delta 108 and nup159-1/r at7-1 mutant strains have little if any defect in nuclear protein import an d 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 f rom the NPCs of the repeat-containing nucleoporin Nup159p.