The transcription factor Krox20 is an E3 ligase that sumoylates its Nab coregulators

Covalent attachment of small ubiquitin-like modifier (SUMO) to proteins regulates many processes in the eukaryotic cell. This reaction is similar to ubiquitination and usually requires an E3 ligase for substrate modification. However, only a few SUMO ligases have been described so far, which frequently facilitate sumoylation by bringing together the SUMO-conjugating enzyme Ubc9 and the target protein. Ubc9 is an interaction partner of the transcription factor Krox20, a key regulator of hindbrain development. Here, we show that Krox20 functions as a SUMO ligase for its coregulators-the Nab proteins-and that Nab sumoylation negatively modulates Krox20 transcriptional activity in vivo. © 2011 EuropeEan MoleEcular Biology Oorganization.This work was supported by BFU2009-10986/BMC (MICINN) and Intramural 200920I085 (CSIC) grants.Peer Reviewe