saw similar discrimination against youthful proteins when they treated the cells to spur production of reactive oxygen species. Older proteins escaped destruction even though they incurred damage. The results indicate that young proteins pass through a vulnerable stage that lasts around an hour. Folding into shape would probably take a few minutes at most, say the authors. But the proteins might also have to join with other proteins to form complexes, undergo structural modifi cations, or move to their home in the cell, during which time they are prone to damage and thus to destruction. Medicherla, B., and A.L. Goldberg. 2008. J. Cell Biol. doi:10.1083/jcb.200803022.