CAPSID DIVERSITY IN SMALL ROUND-STRUCTURED VIRUSES - MOLECULAR CHARACTERIZATION OF AN ANTIGENICALLY DISTINCT HUMAN ENTERIC CALICIVIRUS

Studies of antigenic variation between small round-structured viruses (SRSVs) using immune electron microscopy have revealed 3 antigenic typ es currently circulating in the UK represented by the strains SRSV/Bri /93/UK, SRSV/Sot/91/UK and SRSV/Mel/89/ UK. Mel/89/UK RNA was isolated from a 1989 school outbreak of gastroenteritis. The 3'-terminal 3435 nucleotides (excluding the poly(A) tail) were determined by RT-PCR and cDNA sequencing, completing our molecular characterization of antigen ically diverse SRSVs. Coding regions for the calicivirus RNA polymeras e and capsid protein were found together with a 3' open reading frame of unknown function. The polymerase region was most highly conserved b etween Mel/89/UK and the other two SRSVs while the 3' open reading fra me exhibited extreme variation. Phylogenetic analysis of SRSV capsids showed that Mel/89/UK differed significantly from Bri/93/UK and Sot/91 /UK (62 and 39% identity, respectively) ana was distinct from 6 other non-UK SRSVs that had been previously characterized. This was consiste nt with the designation of Mel/89/UK as a novel antigenic variant. Com parison of the capsid amino acid sequences of the 3 UK strains togethe r with the antigenically distinct SRSV/Nor/68/US revealed a hypervaria ble region that could be surface-exposed and contain the SRSV antigeni c determinants.