To perform the task for which they have been synthesized, proteins must first assemble to form effective cellular “machines.” But how do they recognize their partners at the right time? Researchers at the University of Geneva (UNIGE) have deciphered the fundamental role of the Not1 protein, conserved in all eukaryotic organisms: by regulating the activity of ribosomes, the “protein factories” of cells, Not1 allows proteins that must work together to be synthesized in the same place and at the same time. The identification of this previously unknown mechanism helps to better understand one of the most fundamental elements of cellular machinery, which, if it malfunctions, causes many diseases. Results are published in Nature Structural & Molecular Biology.