Update data files. Update data files. We performed mass spectrometry analysis of Flag-tagged SMURF1 in the presence or absence of VPRBP. Analysis of the SMURF1 interactome and modification by mass spectroscopy examination of the co-immunoprecipitants of Flag-tagged SMURF1. We also applied tandem affinity purification (TAP) assay of the whole proteome to identify interacting proteins of SMAD7. HEK293T cells were transfected with TAP-tagged Smad7, followed by immunoprecipitation, SDS–PAGE, and coomassie staining. SDS–PAGE gels were minimally stained with Coomassie brilliant blue, cut into six molecular weight ranges based on heavy-chain IgG bands, and digested with trypsin. Immunocomplexes were identified on a Thermo Fisher LTQ mass spectrometer. Spectral data were then searched against the human protein RefSeq database in BioWorks or the Proteome Discoverer Suites using either SeQuest (for LTQ data) or Mascot (Orbitrap data) software. The immunoprecipitation–mass spectrometry results were transferred into a FileMaker-based relational database generated in-house,where protein identification numbers (protein GIs) were converted to GeneID identifiers according to the NCBI ‘gene accession’ table.