https://phys.org/news/2019-01-protein-cell-response-stress-immunity.html

The ability of an organism to cope with an ever-changing and challenging environment lies in its ability to activate stress responses. One of the most important biological components affected by stress are the mitochondria—the energy-producing machinery of our cells. Animals respond to mitochondrial stress by activating the UPR—a surveillance program that monitors mitochondrial function and signals to the nucleus (the control centre of the cell) - if something is wrong. Although some components of the UPR have been identified, exactly how it is controlled is still unclear.

"We had previously identified genes that are important for the activation of the mitochondrial stress response," explains lead author Kaiyu Gao, graduate student at the Institute of Molecular Medicine, Peking University, China. "Among these was the ulp-4 gene, which is an enzyme that removes a molecule called SUMO from proteins, dramatically affecting their function. In this study, we set out to see whether the ULP-4 enzyme was necessary for the stress response, and whether it influenced this response by removing SUMO groups."