SEQUENCE DIVERSITY OF SMALL, ROUND-STRUCTURED VIRUSES IN THE NORWALK VIRUS GROUP

We have determined the nucleotide sequences of a highly conserved regi on of the RNA dependent RNA polymerase of the prototype Snow Mountain agent (SMA) and of four other small, round-structured viruses (antigen ically Norwalk virus [NV]-like or SMA-like) following reverse transcri ption-PCR amplification of viral RNA obtained from human stools. The s tool samples were either from volunteers administered SMA or from spor adic cases and outbreaks of gastroenteritis that occurred in Japan and the United Kingdom between 1984 and 1992. The GLPSG and YGDD RNA poly merase motifs were in tile proper locations in the sequences of the fi ve SRSVs, but each sequence was distinct from the 8FIIa prototype NV s equence and from each other. Analysis of the sequences and reactivitie s in a new NV antigen enzyme-linked immunosorbent assay showed that th e five viruses could be divided into two groups (serogroups) with NV a nd SMA, respectively, being the prototypes. The sequences of the capsi d region and a nonstructural region (2C) were determined from one stra in from each group. One virus (SRSV-KY-89/89/J), isolated in Japan and antigenically similar to the prototype NV (isolated 21 years earlier in Ohio), showed a remarkable level of sequence similarity to NV. KY-8 9 and the 8FIIa NV shovved 87.2% nucleotide similarity over 2,516 cont inuous nucleotides amounting to 96 to 98.9% amino acid similarity in t hree distinct domains in two open reading frames. Between the prototyp e SMA and NV, the polymerase region showed 63% nucleotide and 59% amin o acid similarity, respectively. Two other antigenically SMA-like isol ates (SRSV-925/92/UK and SRSV-OTH-25/89/J), from the United Kingdom an d Japan, showed 80% nucleotide and 88 to 92% amino acid similarity in the polymerase region to tile prototype SMA isolated 16 and 13 years e arlier in the United States. The capsid region of the antigenically SR SMA-like OTH-25 virus showed 53% nucleotide and 65% amino acid simila rity to the prototype NV capsid region. Domains of sequence diversity and conservation were identified within the capsid protein of these tw o distinct prototype serotypes of virus. These results indicate that N V-like and SMA-like agents are still circulating, and sequence compari sons will be useful to identify and classify distinct viruses in the N V group.