Role of the UBE2RHTH in diUb formation is determined from kinetic parameters (G-H) for mutants upon titrating the acceptor Ub in pulse-chase reactions following UBE2R2~*Ub Apparent Km and Vmax were determined using the Michaelis-Menten equation (n≥3 independent, technical replicates). Error bars: SEM. Data normalized to the WT apparent Vmax. 