SEQUENCE DIVERSITY WITHIN THE REOVIRUS S3 GENE - REOVIRUSES EVOLVE INDEPENDENTLY OF HOST SPECIES, GEOGRAPHIC LOCALE, AND DATE OF ISOLATION

To better understand genetic diversity of mammalian reoviruses, we stu died sequence variability in the S3 gene segment of 17 field-isolate r eovirus strains and prototype strains of the three reovirus serotypes. Strains studied were isolated over a 37-year period from different ma mmalian hosts and geographic locations. A high degree of variability w as observed in the nucleotide sequences of the S3 gene, whereas the de duced amino acid sequences of the S3 gene product, sigma NS, were high ly conserved. When variability among the S3 nucleotide sequences was a nalyzed using pairwise comparisons, we found that 5' and 3' noncoding regions were significantly more conserved than the remainder of the ge ne. This high degree of sequence conservation was also observed within the first 15 nucleotides of the 5' coding region. Phylogenetic analys es showed that multiple alleles of the S3 gene cocirculate and that ge netic diversity in the S3 gene does not correlate with host species, g eographic locale, or date of isolation. Phylogenetic trees constructed from variation in the S3 sequences are distinct from those previously generated from sequences that encode attachment protein sigma 1, core protein sigma 2, and outer capsid protein sigma 3, which supports the hypothesis that reovirus gene segments reassert in nature. These find ings suggest that reovirus gene segments are well-adapted to mammalian hosts and that reovirus evolution has reached an equilibrium. (C) 199 6 Academic Press, Inc.