This family of proteins is found in eukaryotes and viruses. Proteins in this family are approximately 140 amino acids in length. UL139 product shared sequence homology with human CD24, a signal transducer modulating B-cell activation responses, and the sequences in the G1c variant of UL139 contained a specific attachment site of prokaryotic membrane lipoprotein lipid.

1: Human cytomegalovirus (HCMV) UL139 open reading frame: Sequence variants are clustered into three major genotypes. Qi Y, Mao ZQ, Ruan Q, He R, Ma YP, Sun ZR, Ji YH, Huang Y; J Med Virol. 2006;78:517-522. PMID:16482559