“…Anti-ubiquitin (P4D1) antibodies were purchased from Calbiochem, anti-Troponin T monoclonal (JLT-12) was purchased from Sigma, anti-HA epitope (12CA5) was purchased from Roche Diagnostics, anti-MyoD monoclonal (5.A8) was from Pharmingen, and anti-FLAG (M2) was from Kodak. To inhibit proteasome activity, cells were In Vitro and in Vivo Ubiquitination Assay-Ubiquitination assays were determined essentially as described (17,26) by using [ 35 S]-methionine-labeled in vitro translated HA-MyoD. The recombinant SCF MAFbx complex was produced in insect cells by infection with baculovirus encoding HA-MAFbx-His 6 , Skp1, Cul1, and Rbx1, purified by nickel-agarose chromatography, and added in roughly similar amount to the reaction.…”