Translation initiation factor eIF1A rescues hygromycin B sensitivity caused by deleting the carboxy-terminal tail in the GPN-loop GTPase Npa3

• Published in: The FEBS journal Vol. 291; no. 10; pp. 2191 - 2208
• Main Authors: Félix-Pérez, Tania, Mora-García, Martín, Rebolloso-Gómez, Yolanda, DelaGarza-Varela, Alda, Castro-Velázquez, Grecia, Peña-Gómez, Sonia G, Riego-Ruiz, Lina, Sánchez-Olea, Roberto, Calera, Mónica R
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-05-2024
• Subjects: Amino acids; Aminoglycoside antibiotics; Aminoglycosides; Antibiotics; Biological activity; Cell growth; Cell Nucleus - genetics; Cell Nucleus - metabolism; Cell proliferation; DNA-directed RNA polymerase; Gene expression; Geneticin; GTP Phosphohydrolases - genetics; GTP Phosphohydrolases - metabolism; Hygromycin; Hygromycin B; Hygromycin B - pharmacology; Inhibitors; Localization; Mutants; Mycophenolic acid; Nuclear transport; Phenotypes; Polypeptides; Protein biosynthesis; Protein Biosynthesis - drug effects; Protein synthesis; Protein Synthesis Inhibitors - pharmacology; Proteins; Puromycin; RNA polymerase; RNA polymerase II; RNA Polymerase II - genetics; RNA Polymerase II - metabolism; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - growth & development; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Sensitivity; Transcription elongation; Yeast; Yeasts; Npa3; hygromycin B; protein synthesis; TIF11/eIF1A
• ISSN: 1742-464X; 1742-4658; 1742-4658
• DOI: 10.1111/febs.17106

The essential yeast protein GPN-loop GTPase 1 (Npa3) plays a critical role in RNA polymerase II (RNAPII) assembly and subsequent nuclear import. We previously identified a synthetic lethal interaction between a mutant lacking the carboxy-terminal 106-amino acid tail of Npa3 (npa3ΔC) and a bud27Δ mutant. As the prefoldin-like Bud27 protein participates in ribosome biogenesis and translation, we hypothesized that Npa3 may also regulate these biological processes. We investigated this proposal by using Saccharomyces cerevisiae strains episomally expressing either wild-type Npa3 or hypomorphic mutants (Npa3ΔC, Npa3K16R, and Npa3G70A). The Npa3ΔC mutant fully supports RNAPII nuclear localization and activity. However, the Npa3K16R and Npa3G70A mutants only partially mediate RNAPII nuclear targeting and exhibit a higher reduction in Npa3 function. Cell proliferation in these strains displayed an increased sensitivity to protein synthesis inhibitors hygromycin B and geneticin/G418 (npa3G70A > npa3K16R > npa3ΔC > NPA3 cells) but not to transcriptional elongation inhibitors 6-azauracil, mycophenolic acid or 1,10-phenanthroline. In all three mutant strains, the increase in sensitivity to both aminoglycoside antibiotics was totally rescued by expressing NPA3. Protein synthesis, visualized by quantifying puromycin incorporation into nascent-polypeptide chains, was markedly more sensitive to hygromycin B inhibition in npa3ΔC, npa3K16R, and npa3G70A than NPA3 cells. Notably, high-copy expression of the TIF11 gene, that encodes the eukaryotic translation initiation factor 1A (eIF1A) protein, completely suppressed both phenotypes (of reduced basal cell growth and increased sensitivity to hygromycin B) in npa3ΔC cells but not npa3K16R or npa3G70A cells. We conclude that Npa3 plays a critical RNAPII-independent and previously unrecognized role in translation initiation.