Nuclear basket subunits Nup211 and Rsm1 influence RNA 3′-processing and transcription termination in fission yeast

The fission yeast phosphate acquisition (PHO) regulon is repressed under phosphate-replete conditions by upstream lncRNA-mediated transcriptional interference. Inositol-1-pyrophosphates control PHO gene expression via their action as agonists of precocious PHO lncRNA 3'-processing/termination. Inositol pyrophosphatase-inactivating asp1-STF mutations that increase inositol-1-pyrophosphates elicit derepression of the PHO genes and a severe growth defect in YES medium. Previous studies demonstrated suppression of inositol pyrophosphate toxicosis by loss-of-function and hypomorphic mutations in 11 of the 14 subunits of the fission yeast Cleavage and Polyadenylation Factor (CPF) complex. Here, we report the identification and characterization of mutations in the Nup211 and Rsm1 subunits of the nuclear basket of the nuclear pore complex that suppress inositol pyrophosphate toxicosis. We localize Nup211's activity in asp1-STF toxicosis to the C-terminal segment that forms a globular module appended to the dimeric Nup211 coiled-coil of the nuclear basket strut. A triple-alanine mutation of a conserved Nup211 1821RDD1823 peptide sufficed to suppress asp1-STF toxicosis. We find that: (i) induced overexpression of the Nup211 C-terminal segment is itself toxic to fission yeast, and that this toxicity was abolished by the RDD-AAA mutation; and (ii) Nup211 C-terminal truncation confers synthetic growth defects when combined with loss-of-function mutations in CPF subunits Ppn1, Swd22, and Ssu72. Our results implicate the Nup211 C-terminus as part of a protein-protein interface that abets 3'-processing/termination.