Molecular characterization of eight segments of Scylla serrata reovirus (SsRV) provides the complete genome sequence

Scylla serrata reovirus (SsRV) is one of the most prevalent viral pathogens of mud crabs (S. serrata). Of the 12 double-stranded RNA (dsRNA) genomic segments (S1–S12), the three largest (S1–S3) and S7 were sequenced previously and were shown to have no or only low sequence homology to known members within the family Reoviridae. The sequences of the remaining segments, S4–S6 and S8–S12, are reported here. With the exception of S4, all have single open reading frames (ORFs) on their positive strands, and the terminal sequences 5′-AUAAA^U/_C ^A/_U…G^A/_G ^A/_U ^A/_CAAC^G/_UAU-3′ are conserved among currently and previously sequenced segments. S4 contains two out-of-phase ORFs on the positive strand, suggesting that this segment is bicistronic. The ORFs of segments S4–S6 and S8–S12 have low or no homology to other reovirus genes, with the exception that all of the SsRV segments have high sequence similarity to those of mud crab reovirus (MCRV) and share the same 5′- and 3′-terminal nucleotide sequences, suggesting that the two viruses belong to the same species in the family Reoviridae. Analysis of virion proteins revealed that SsRV contains at least eight structural proteins, with sizes ranging from 25 to 160 kDa.