E3 ubiquitin ligase that, together with UBE2N and UBE2V1, mediates the synthesis of 'Lys-63'-linked-polyubiquitin chains conjugated to proteins, such as ECSIT, IKBKG, IRAK1, AKT1 and AKT2.Also mediates ubiquitination of free/unanchored polyubiquitin chain that leads to MAP3K7 activation.