A new protein, SNOR, discovered in yeast cells acts as a master switch, putting ribosomes into a protective sleep during starvation and being essential for waking them up when food returns.
Scientists from EMBL and the University of Virginia have identified a novel protein in yeast cells that plays a critical role in managing cellular energy. The study, published in Nature, details how SNOR attaches to ribosomes during glucose deprivation, inducing a state of hibernation that is crucial for survival.
Key Discovery
Using advanced imaging techniques like cryo-electron tomography (cryo-ET) and visual proteomics, researchers visualized SNOR binding directly to ribosomes inside living cells. This binding event triggers a significant drop in the cell's protein-building efficiency.
Unlike many cellular processes that are simply shut down, SNOR's role is more nuanced. While its expression reduces translation efficiency, it does not single-handedly initiate dormancy. The process also requires a "hibernation factor" known as eIF5A. The true test of SNOR's importance came when glucose was reintroduced: in SNOR-knockdown cells, ribosomes remained inactive and could not restart protein synthesis even 30 minutes after nutrients returned.
A Window into Cellular Survival
The research builds on previous findings that yeast ribosomes cluster around mitochondria during starvation. The discovery of SNOR now provides a long-sought regulatory mechanism for this behavior.
The high-resolution 3D reconstructions made possible by cryo-ET were essential, revealing a previously uncharacterized protein that traditional methods had missed. This success highlights the power of "visual proteomics" for identifying unknown proteins and their functions directly within the cell.
Implications and Future Research
Understanding how cells enter and exit a dormant state has broad implications for medicine, agriculture, and biotechnology. For instance, controlling this mechanism could prevent the "waking up" of dormant cancer cells.
Future research will focus on how SNOR itself is activated to signal the restart of protein synthesis, as well as the signaling pathways governing this process. Scientists are also keen to understand why ribosomes specifically cluster around mitochondria during starvation.
A Key Limitation
It is important to note that SNOR has currently been found only in yeast and other fungi. The analogous factors that perform this crucial function in other organisms, including humans, remain to be discovered.