The nucleolus is a well-known cellular structure that is easily visible under a light microscope. This nuclear structure is known as the site of ribosome production. In a recent study, researchers at the Max Planck Institute of Biochemistry in Martinsried, Germany, have shown that the nucleolus is also a site of quality control for proteins. When cells are stressed, proteins tend to misfold and to aggregate. To prevent proteins from clumping, some are temporarily stored in the nucleolus. The special biophysical conditions found in this organelle prevent harmful protein aggregation. The results of this study have now been published in the journal Science.