A NOVEL NUCLEAR-PORE PROTEIN NUP133P WITH DISTINCT ROLES IN POLY(A)(-PORE DISTRIBUTION() RNA TRANSPORT AND NUCLEAR)

Temperature-sensitive nucleoporin nup49-316 mutant cells accumulate po ly(A)(+) RNA inside the nucleus when shifted to restrictive temperatur e. We performed a synthetic lethal screen with this mutant allele to i dentify further components of the mRNA export machinery. A synthetic l ethal mutant slv21 was isolated, which exhibited a ts phenotype and sh owed nuclear accumulation of poly(A)(+) RNA at 37 degrees C. The wild- type gene complementing slv21 was cloned and sequenced. It encodes a n ovel protein Nup133p which is located at the nuclear pore complex. NUP 133 is not an essential gene, but cells in which NUP133 is disrupted g row slowly at permissive temperatures and stop growing at 37 degrees C . Concomitant with the growth inhibition, nup133(-) cells accumulate p oly(A)(+) RNA inside the nucleus whereas nuclear import of a karyophil ic reporter protein is not altered. Strikingly, nup133(-) cells displa y extensive clustering of nuclear pore complexes at a few sites on the nuclear envelope. However, the nuclear pore clustering phenotype and intranuclear accumulation of poly(A)(+) RNA are not obligatorily linke d, since an amino-terminally truncated Nup133p allows normal poly(A)() RNA export, but does not complement the clustering phenotype of nup1 33(-) cells.