Variation in ORF3 of genogroup 2 Norwalk-like viruses.

The nucleotide sequences of the 3'-terminal open reading frame (ORF3) and 3' untranslated region (3'UTR) were determined for four Norwalk-like viruses (NLVs) belonging to genogroup 2. Three of the viruses, isolated in 1995 and 1996, were closely related to Mexico virus (92-93% nucleotide identity in ORF3). The fourth virus, isolated in 1984, was unique, showing only 49-58% nucleotide identity with other NLVs. The variation in sequence of the 3'-terminal ORF of NLVs was greater than that observed for other caliciviruses. This variation was partly due to repeated sequences and frameshifting. To investigate the properties of the ORF3 encoded polypeptide, a signal sequence and N-linked glycosylation sites predicted for Camberwell virus were tested for function by in vitro translation in the presence of microsomes. Membrane insertion, cleavage of an N-terminal signal sequence, or glycosylation were not detected.