A ubiquitin ligase complex consisting of MUB1, RAD6 and UBR2 components. It ubiquitinates, and targets for destruction, the RPN4 transcription factor, which upregulates the proteasome genes. The binding of MUB1 may position the RPN4 ubiquitylation site proximal to the Ubiquitin-RAD6 thioester and allow the transfer of Ubiquitin from RAD6 to RPN4. One of its components, MUB1, is a short-lived protein ubiquitinated by the UBR2-RAD6 ubiquitin conjugating enzyme. [ http://www.ncbi.nlm.nih.gov/pubmed/18070918 ]