Structural domains comprising this superfamily share the structure of the C-terminal domain, designated domain 2, of the multifunctional birnavirus protein VP3, involved in virus morphogenesis. VP3 interacts with the structural protein VP2, with the double-stranded RNA genome, and with the virus-encoded, RNA-dependent RNA polymerase (RdRP), VP1, playing a role in both viral capsid formation, recruitment of VP1 into the capsid and encapsidation of the viral genome. The fold of this domain shows significant structural similarities with different transcription regulation factors which suggests it mediates interaction with both the genome and RdRP PMID:18184581.