Molecular characterization of L class genome segments of a newly isolated turkey arthritis reovirus

- We have sequenced L class genes of newly isolated turkey arthritis reovirus.
- Turkey arthritis reovirus closely related to chicken arthritis reovirus.
- Point mutations and reassortments observed.
- Proposed new nucleotide cut-off value for each L gene for defining genotype of ARV.

Seven strains of turkey arthritis reovirus (TARV) isolated from cases of turkey arthritis were characterized on the basis of their L class genome segment sequences, which were then compared with those of turkey enteric reovirus (TERV) and chicken reovirus (CRV). All three L class gene segments of TARVs and TERVs and their encoded proteins λA, λB, and λC were similar in size to those of CRV reference strain S1133. The conserved motifs such as C2H2 zinc-binding motif and conserved polymerase region were present in λA and λB, respectively. A conserved motif for ATP/GTP-binding site and an S-adenosyl-l-methionine (SAM)-binding pocket for methyltransferase were observed in λC protein of TARVs and TERVs with only one substitution as compared to that in CRV. We propose a new genotype classification system for avian reoviruses (ARVs) based on the nt identity cut-off value for each of the L class. Based on this new genotype classification, all ARVs were divided into six, seven and eight genotypes in L1, L2 and L3 genes, respectively. Interestingly TARVs and TERVs grouped with three CRVs (two arthritic strains from Taiwan and one enteritic strain from Japan) in genotype L1-I and formed a different genotypes (L2-I, L3-I) from CRVs in L2 and L3 genes. The maximum nucleotide divergence was observed in genotypes of L1 and L2 genes but less at amino acid level indicates mostly changes were synonymous type. Compared to L1 and L2 genes, the nonsynonymous changes were more in L3 gene. Point mutations and possible reassortments among TARVs, TERVs and CRVs were also observed.