Files in this Data Supplement:

• Supplemental file 1 - Supplemental text, Table S1 (Complete list of known and predicted E3 ubiquitin ligases screened), and Fig. S1 (Results from the E3 ubiquitin ligase screen), S2 (Smad7 siRNA efficiently knockdown Smad7), S3 (Decrease of SnoN nuclear protein level upon TGF-β stimulation is due to its degradation by the proteasome), S4 (Knockdown of Arkadia with two different siRNAs abolishes SnoN degradation upon TGF-β stimulation), S5 (Smad2 and Smad3 are redundant for SnoN degradation), and S6 (The activator effect of Arkadia on Smad3/4-dependent transcription is abolished by SnoN overexpression)
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