Nonessential nucleoporins Nup2, Nup60 and Nup84 are required for normal meiosis in budding yeast

Abstract

The nuclear pore complex (NPC) selectively transports cargo between the nucleus and the cytoplasm. The inner nuclear membrane (INM) face of the NPC also serves as a hub where gene silencing and DNA repair are spatially coordinated. In Saccharomyces cerevisiae, partitioning of active and silenced chromatin at subtelomeric regions depends on the boundary activity of nonessential nucleoporin proteins Nup2 and Nup60, along with Htz1, the histone variant H2A.Z. The INM is also important for the chromosome events of meiosis since Ndj1-mediated telomere attachment and clustering at the INM is required for efficient homolog pairing, recombination, and segregation. Here we tested possible meiotic roles for Nup2, Nup60, Htz1, and other nonessential nucleoporins by analyzing the effects of deletion mutations on sporulation, spore viability and possible phenotypic epistasis with ndj1{Delta}. Deleting NUP2, NUP60, and HTZ1 reduced spore viability compared to wild-type (WT). A detailed analysis of spore lethality indicated that homolog nondisjunction in these mutants was elevated compared to WT, yet unlike ndj1{Delta}, this was not the predominant cause of spore death. Deleting NUP84 reduced meiosis I nuclear divisions, while deleting NUP53, NUP100, and NUP157 had no effect on sporulation, spore viability, or the kinetics of meiosis I progression. Surprisingly, nup2{Delta} ndj1{Delta} uniquely failed to undergo meiosis I nuclear divisions, suggesting Nup2 and Ndj1 function in partially redundant pathways or create a poisonous intermediate. The meiosis I division was also delayed by 2 hours in nup2{Delta} compared to WT pointing to a specialized role for Nup2 in the meiotic program.