The ubiquitin proteasome system is important in the regulation of many nucleocytosolic processes. However, its regulatory reach was not thought to extend to the chloroplast. Using a forward-genetic screen in Arabidopsis, Ling et al. (see the Perspective by Kessler) identified a ubiquitin E3 ligase, termed SP1, embedded in the chloroplast outer envelope membrane. SP1 was found to target components of the chloroplast protein import machinery for degradation by the ubiquitin proteasome and was important for changes in chloroplast biogenesis.