We reported a novel mammalian reovirus, designed BYD1, isolated from throat swabs of patients with severe acute respiratory syndrome （SARS）, in 2003. In the present study, we firstly compared the genome electrophoretic migration patterns of reovirus BYD1 with 3 prototype reovirus strains by polyacrylamide gel electrophoresis （PAGE） and determined the complete nucleotide sequence of the S1 gene segment of BYD1 by single primer amplification technique. The electropherogram of BYD1 was different from those of the 3 prototype strains and any other reovirus isolates reported before. The entire S1 segment sequence of BYD1 is 1437 bp long with two meaningful open reading frames （ORFs）. The longest ORF encodes σ1, the cell attachment protein, and the second longest ORF supposedly encodes σ1s, an important nonstructural virulence factor. The terminal sequences of SI segment are 5＇GCUA and 3＇UCAUC, which are consistent with those of other mammalian reoviruses. The highest homology of deduced σ1 amino acid sequence is 64% identity with known mammalian reoviruses. Phylogenetic analysis of both S1 nucleotide sequence and σ1 amino acid sequence indicated the BYD1 isolate belonged to a new clade of serotype 2 group. The results of this study showed that the BYD1 S1 segment was markedly different from those of isolates reported before and BYD1 was a novel human reovirus isolate.
