(a) Time course comparing the in vitro ubiquitination of 4xSUMO2, using both native and methylated Ub, by RNF4 in the presence of UBCH5B. Reactions contained 200 nM E1, 5 μM E2, 1 μM RNF4, 15 μM 4xSUMO-2 and 100 μM of native or methylated Ub, and were incubated at 37°C. Samples were analyzed by SDS-PAGE, followed by Coomassie Brilliant Blue stain. (b) Time course comparing the in vitro ubiquitination of 4xSUMO2, using both native and methylated Ub, by RNF4 in the presence of RAD6B. Reactions contained 200 nM E1, 5 μM E2, 1 μM RNF4, 15 μM 4xSUMO-2 and 100 μM of native or methylated Ub, and were incubated at 37°C. Samples were analyzed by SDS-PAGE, followed by Coomassie Brilliant Blue stain.