C In vitro ubiquitination assay for NEMO-K326R. HEK293T cells were transfected with GST-tagged NEMO, GST-tagged NEMO-K326R or Strep-tagged MARCH2 individually. Immunoprecipitates were incubated with a reaction mixture containing ubiquitin, E1, and UbcH6 (E2), followed by immunoblotting with an anti-K48-linkage specific polyubiquitin antibody. 