2 NOVEL RELATED YEAST NUCLEOPORINS NUP170P AND NUP157P - COMPLEMENTATION WITH THE VERTEBRATE HOMOLOG NUP155P AND FUNCTIONAL INTERACTIONS WITH THE YEAST NUCLEAR PORE-MEMBRANE PROTEIN POM152P

We have taken a combined genetic and biochemical approach to identify major constituents of the yeast nuclear pore complex (NPC). A syntheti c lethal screen was used to identify proteins which interact genetical ly with the major pore-membrane protein Pom152p. In parallel, polypept ides present in similar amounts to Pom152p in a highly enriched prepar ation of yeast NPCs have been characterized by direct microsequencing. These approaches have led to the identification of two novel and majo r nucleoporins, Nup170p and Nup157p. Both Nup170p and Nup157p are simi lar to each other and to an abundant mammalian nucleoporin, Nup155p (R adu, A., G. Blobel, and R. W. Wozniak. 1993. J. Cell Biol. 121: 1-9) a nd inter estingly, nup170 mutants can be complemented with mammalian N UP155. In addition, the synthetic lethal screen identified genetic int eractions between Pom152p and two other major nucleoporins, Nup188p (N ehrbass, U., S. Maguire, M. Rout, G. Blobel, and R. W. Wozniak, manusc ript submitted for publication), and Nic96p (Grandi, P., V. Doye, and E. C. Hurt. 1993. EMBO J. 12: 3061-71). We have determined that togeth er, Nup170p, Nup157p, Pom152p, Nup188p, and Nic96p comprise greater th an one-fifth of the mass of the isolated yeast NPC. Examination of the genetic interactions between these proteins indicate that while delet ion of either POM152, NUP170, or NUP188 alone is not lethal, pairwise combinations are. Deletion of NUP157 is also not lethal. However, nup1 57 null mutants, while lethal in combination with nup170 and nup188 nu ll alleles, are not synthetically lethal with pom152 null alleles. We suggest that Nup170p and Nup157p may be part of a morphologically symm etrical but functionally distinct substructure of the yeast NPC, e.g., the nucleoplasmic and cytoplasmic rings. Finally, we observed morphol ogical abnormalities in the nuclear envelope as a function of alterati ons in the expression levels of NUP170 suggesting a specific stoichiom etric relationship between NPC components is required for the maintena nce of normal nuclear structure.