Immunoblots of SDS lysates from M1 MEFs infected with HA-Sumo2 retroviral expression vector (lanes 2, 4, 6, and 8) or empty HA vector (lanes 1, 3, 5, and 7). Direct analysis with anti-HA (lane 2) or anti-HA immunoblotting of anti-HA immunoprecipitates (lane 4) shows HA-Sumo2/3 conjugates across the full range of molecular masses. Analysis of anti-HA immunoprecipitates with anti-Sumo1 (lane 8) reveals only HMM species (bracket), suggesting that these represent long poly-Sumo2/3 chains capped with Sumo1.