Genetic and Biochemical Interactions Among Yar1, Ltv1 and RpS3 Define Novel Links Between Environmental Stress and Ribosome Biogenesis in Saccharomyces cerevisiae

Abstract

In the yeast S. cerevisiae, ribosome assembly is linked to environmental conditions by the coordinate transcriptional regulation of genes required for ribosome biogenesis. In this study we show that two nonessential stress-responsive genes, YAR1 and LTV1, function in 40S subunit production. We provide genetic and biochemical evidence that Yar1, a small ankyrin-repeat protein, physically interacts with RpS3, a component of the 40S subunit, and with Ltv1, a protein recently identified as a substoichiometric component of a 43S preribosomal particle. We demonstrate that cells lacking YAR1 or LTV1 are hypersensitive to particular protein synthesis inhibitors and exhibit aberrant polysome profiles, with a reduced absolute number of 40S subunits and an excess of free 60S subunits. Surprisingly, both mutants are also hypersensitive to a variety of environmental stress conditions. Overexpression of RPS3 suppresses both the stress sensitivity and the ribosome biogenesis defect of ⌬yar1 mutants, but does not suppress either defect in ⌬ltv1 mutants. We propose that YAR1 and LTV1 play distinct, nonessential roles in 40S subunit production. The stresssensitive phenotypes of strains lacking these genes reveal a hitherto unknown link between ribosome biogenesis factors and environmental stress sensitivity.

Essential ribosome assembly factor Fap7 regulates a hierarchy of RNA–protein interactions during small ribosomal subunit biogenesis

“…Indeed Fap7 is not the only ribosome assembly factor described to be responsible for protecting a ribosomal protein from such detrimental effects before incorporation into the nascent ribosome. The chaperones Sqt1, Rrb1, and Yar1 have been shown to bind to the ribosomal proteins Rpl10, Rpl3, and Rps3, respectively, which all contain long basic N-or Cterminal extensions (29)(30)(31). The 50-aa C-terminal extension of Rpl10, for example, has been shown to directly interact with its chaperone Sqt1.…”

Ankyrin Repeat: A Unique Motif Mediating Protein−Protein Interactions

“…Besides CDK4 and CDK6, p16 binds to and negatively regulates transcription factor NF-κB (62) and c-Jun kinase (64) under physiological conditions (Figure 5b). As for gankyrin, its physiological partners include CDK4 (56,58), Rb (65), S6 ATPase of the 26S proteasome (61), MAGE-A4 antigen (66), and HDM2 (67) (Figure 5c). Binding of gankyrin to Rb, S6 ATPase of the 26S proteasome, and HDM2 facilitates the ubiquitin-mediated degradation of Rb, HDM2, and other proteins (65,(67)(68)(69), while binding of gankyrin to MAGE-A4 quenches the oncogenic activity of gankyrin through unknown mechanisms (66).…”

Genetic Analysis of the Ribosome Biogenesis Factor Ltv1 ofSaccharomyces cerevisiae

“…Cells lacking any Ltv1 (Dltv1) are slow growing at low temperature and produce about half as many 40S subunits as wild-type cells do (Loar et al 2004). If these phenotypes are due to a role of Ltv1 in pre-40S export, then expression of the export-defective Ltv1DNES protein should not complement these Dltv1 phenotypes.…”

“…Overexpression of Rps3 in cells overexpressing Ltv1ΔC13 did not rescue the dominant-negative phenotype. However, RpS3 has a binding partner and proposed chaperone, Yar1 (Loar et al 2004), which increases its solubility (Koch et al 2012). We therefore transformed cells overexpressing Ltv1ΔC13 with both YAR1 and RPS3 plasmids.…”

“…Titration of free RpS3 by overexpressed Ltv1DNES might deleteriously affect growth if free extraribosomal RpS3 plays a role in DNA surveillance and, hence, in cell division in yeast. The fact that both Dyar1 and Dltv1 cells are sensitive to oxidative stress (Loar et al 2004) might be related to their common affinity for and interaction with RpS3, perhaps in this nonribosomal role of the protein.…”