This protein is found in archaea and viruses. Proteins in this family are typically between 265 to 342 amino acids in length. The proteins in this family are or are related to the m04 encoded protein gp34 of pathogenic microorganisms such as murine cytomegalovirus. m06 and m152 genes are expressed earlier in the intracellular replication phases of these microorganism' life cycles. They function to inhibit MHC-1 loading and export. gp34 is theorized to prevent immune reactions from NK cells which would ordinarily recognize and attack cells lacking MHC.