Conserved structure/function of the orthoreovirus major core proteins.

Orthoreoviruses are infectious agents with genomes of 10 segments of double-stranded RNA. Detailed molecular information is available for all 10 segments of several mammalian orthoreoviruses, and for most segments of several avian orthoreoviruses (ARV). We, and others, have reported sequences of the L2, all S-class, and all M-class genome segments of two different avian reoviruses, strains ARV138 and ARV176. We here determined L1 and L3 genome segment nucleotide sequences for both strains to complete full genome characterization of this orthoreovirus subgroup. ARV L1 segments were 3958 nucleotides long and encode λA major core shell proteins of 1293 residues. L3 segments were 3907 nucleotides long and encode λC core turret proteins of 1285 residues. These newly determined ARV segments were aligned with all currently available homologous mammalian reovirus (MRV) and aquareovirus (AqRV) genome segments. Identical and conserved amino acid residues amongst these diverse groups were mapped into known mammalian reovirus λ1 core shell and λ2 core turret proteins to predict conserved structure/function domains. Most identical and conserved residues were located near predicted catalytic domains in the λ-class guanylyltransferase, and forming patches that traverse the λ-class core shell, which may contribute to the unusual RNA transcription processes in this group of viruses.