E6-AP/UBE3A protein acts as a ubiquitin ligase toward SOX9 protein.

SOX9 is a transcription factor that acts as a key regulator at various stages of cartilage differentiation. There is ample evidence that intracellular SOX9 protein levels are tightly regulated both by sumoylation and by degradation through the ubiquitin-proteasome pathway. Using a proteomics approach, here we report the identification of a SOX9-binding protein, E6-AP/UBE3A, that may act as a ubiquitin ligase toward Sox9.