Characterization of the NSP4 gene of group A human rotavirus G1P[8] strains circulating in Sapporo, Japan from 1987 to 2000.

The genetic diversity of the NSP4 gene of rotavirus G1P[8] strains obtained in Sapporo was analyzed, Japan from 1987 to 2000. Sixty-four strains, which were distributed across the whole study period, were included. All G1P[8] NSP4 genes detected in this study belonged to genotype E1, which divided into at least three lineages. The Sapporo rotavirus G1P[8] isolates were found in each lineage. The mean estimated substitution rate was 1.40 × 10(-3) nucleotide substitutions per site per year, which was comparable to that of the G1P[8] VP7 gene. Comparison of the deduced NSP4 amino acid sequences showed genetic diversity at the center of antigenic site II, but not in the enterotoxic domain. This report represents the first investigation of the genetic diversity and evolution of group A rotavirus NSP4 genes in Asia.