bims-tricox 2026-08-02 papers

Issue of 2026–08–02
three papers selected by
Yash Verma, Universität Zürich

Genetics. 2026 Aug 01. pii: iyag200. [Epub ahead of print]

Ribosome-associated chaperones integrate co-translational mitochondrial protein import, stress signaling and proteostasis in Saccharomyces cerevisiae.

J Ernesto Bravo-Arévalo, Ariann E Mendoza-Martínez, Teresa Ballado, Ericka Moreno-Méndez, Alexander DeLuna, Soledad Funes.

Mitochondrial biogenesis requires the coordinated synthesis, targeting, and import of nuclear-encoded mitochondrial precursor proteins. Although ribosome-associated chaperones support co-translational protein folding, their genetic contributions to mitochondrial protein import and cellular homeostasis remain incompletely defined. Here, we investigate the roles of the nascent polypeptide-associated complex (NAC) and the ribosome-associated Hsp70 system Ssb1/2 in Saccharomyces cerevisiae. We show that NAC and Ssb1/2 have distinct yet partially overlapping functions in the handling of mitochondrial precursor proteins. Loss of NAC activates the mitochondrial retrograde pathway and enhances growth on ethanol as a non-fermentable carbon source without compromising respiratory competence, indicating metabolic adaptation rather than overt mitochondrial dysfunction. In contrast, Ssb1/2 deficiency disrupts cytosolic proteostasis, sensitizes cells to TORC1 inhibition, and impairs autophagy and mitophagy. Using a TEV protease-based import reporter, we show that Ssb1/2 promotes efficient co-translational distribution of precursor proteins, whereas NAC limits the accumulation of misfolded proteins at the mitochondrial surface. Biochemical analyses further reveal that Ssb1/2 supports the association of translating cytosolic ribosomes with the mitochondrial outer membrane, while NAC loss partially restores this interaction in the absence of Ssb1/2. Together, these findings establish NAC and Ssb1/2 as key components of an integrated network linking co-translational targeting, mitochondrial signaling, and cellular homeostasis.

Keywords: Saccharomyces cerevisiae ; Ribosome-associated chaperones; TORC1 signaling; co-translational targeting; mitochondrial protein import; proteostasis; retrograde signaling

DOI: https://doi.org/10.1093/genetics/iyag200

Microbiol Mol Biol Rev. 2026 Jul 30. e0015925

Falling asleep: the importance of ribosome hibernation in bacteria.

Robert Karari Njenga, Hans-Georg Koch.

SUMMARYThe biogenesis of ribosomes and protein synthesis are among the most energy-consuming processes in living cells and therefore rate-limiting for growth, making them key targets for controlling the growth of competitors, predators, and pathogens. Cells also restrict their own protein synthesis under nutrient limitation or other stress conditions. A universally conserved strategy involves ribosome hibernation, in which specialized factors reversibly silence ribosomes. This protects ribosomes from being degraded by RNases and proteases, and at the same time allows for their fast reactivation when conditions improve. In bacteria, multiple hibernation factors act in parallel through distinct mechanisms. Well-characterized factors, such as ribosome modulation factor (RMF) and hibernation-promoting factor (HPF) and its homologs, block the mRNA channel and occupy the A- and P-sites of the small ribosomal subunit. Other factors, such as ribosome silencing factor S (RsfS), prevent the association of the 30S ribosomal subunit with the 50S subunit. Recently characterized factors include the paralogous C-tail-anchored membrane proteins YqjD, ElaB, and YgaM, which inactivate ribosomes by blocking the peptide exit tunnel. The coordinated production of these factors is tightly linked to broader stress response pathways, ensuring that ribosomal activity is modulated in accordance with cellular needs. In this review, we describe the diverse mechanisms that bacteria such as E. coli use to silence ribosomes and highlight the flexibility and significance of ribosome hibernation as a conserved strategy for saving energy and for cellular adaptation to stress conditions.

Keywords: dormancy; ribosome hibernation; stress response; stringent response

DOI: https://doi.org/10.1128/mmbr.00159-25