D In vivo ubiquitination assay. 293T cells were transiently transfected with HA-ubiquitin and Myc-DNMT3A. After 24 hours, cells were treated with or without MG132 for 2 hours at the indicated concentrations, followed by ATO co-treatment for 6 hours at the indicated concentrations. Myc-DNMT3A was immunoprecipitated (IP) with anti-Myc antibody, followed by immunoblotting (IB) as indicated. 