J Negative charges at the E2HTH weakens the diUb synthesis activity of the E2 family. Electrostatic models of the UBE2S, UBE2C, UBE2D2, and UBE2R2 HTH motifs were generated using the PBEQ solver (Jo et al, 2008). Active site cysteine is indicated as a yellow sphere. Negative to positive charge represented as a red to blue gradient. 