Recently, novel E3 ubiquitin ligases that target MHC molecules for lysosomal degradation have been discovered by several groups. All these E3s are membrane-bound and possess a variant type RING domain, termed the RING-CH or RING variant (RINGv) domain. They belong to a new E3 family designated Modulator of Immune Recognition (MIR), based on the name of the first identified family members. The discovery of the MIR family has provided fresh insight into viral pathogenesis and immune regulation.