GLE2, A SACCHAROMYCES-CEREVISIAE HOMOLOG OF THE SCHIZOSACCHAROMYCES-POMBE EXPORT FACTOR RAE1, IS REQUIRED FOR NUCLEAR-PORE COMPLEX STRUCTURE AND FUNCTION

To identify and characterize novel factors required for nuclear transp ort, a genetic screen was conducted in the yeast Saccharomyces cerevis iae. Mutations that were lethal in combination with a null allele of t he gene encoding the nucleoporin Nup100p were isolated using a colony- sectoring assay. Three complementation groups of gle (for GLFG lethal) mutants were identified. In this report, the characterization of GLE2 is detailed. GLE2 encodes a 40.5-kDa polypeptide with striking simila rity to that of Schizosaccharomyces pombe RAE1. In indirect immunofluo rescence and nuclear pore complex fractionation experiments, Gle2p was associated with nuclear pore complexes. Mutated alleles of GLE2 displ ayed blockage of polyadenylated RNA export; however, nuclear protein i mport was not apparently diminished. Immunofluorescence and thin-secti on electron microscopic analysis revealed that the nuclear pore comple x and nuclear envelope structure was grossly perturbed in gle2 mutants . Because the clusters of herniated pore complexes appeared subsequent to the export block, the structural perturbations were likely indirec t consequences of the export phenotype. Interestingly, a two-hybrid in teraction was detected between Gle2p and Srp1p, the nuclear localizati on signal receptor, as well as Rip1p, a nuclear export signal-interact ing protein. We propose that Gle2p has a novel role in mediating nucle ar transport.