Cells have their own quality control to prevent the production and accumulation of harmful proteins. This quality control is essential for correct embryonic development in all mammals and plays an important role in tumors and genetic diseases such as cystic fibrosis. A group of researchers from the University of Bern and the University of Basel have now made visible and cataloged for the first time, "blueprints" that give rise to defective proteins and are normally recognized and rapidly degraded in cells. This leads to a better understanding of this degradation mechanism and helps in the development of new therapeutic approaches.