F-box proteins everywhere.

The ubiquitin proteasome system is a key regulator of many biological processes in all eukaryotes. This mechanism employs several types of enzymes, the most important of which are the ubiquitin E3 ligases that catalyse the attachment of polyubiquitin chains to target proteins for their subsequent degradation by the 26S proteasome. Among the E3 families, the SCF is the best understood; it consists of a multi-protein complex in which the F-box protein plays a crucial role by recruiting the target substrate. Strikingly, nearly 700 F-box proteins have been predicted in Arabidopsis, suggesting that plants have the capacity to assemble a multitude of SCF complexes, possibly controlling the stability of hundreds of substrates involved in a plethora of biological processes. Interestingly, viruses and even pathogenic bacteria have also found ways to hijack the plant SCF and to reprogram it for their own purposes.