Snow Mountain virus genome sequence and virus-like particle assembly

Snow Mountain virus (SMV) belongs to the Norovirus genus of the Caliciviridae family. SMV is a genogroup II (GII) reference strain of human enteric caliciviruses associated with epidemic gastroenteritis. In this study, the positive sense RNA genome sequence of SMV was determined to be 7,537 nucleotides in length excluding the 3' polyadenylated tract. The genome is organized into three open reading frames typical of caliciviruses in the Norovirus genus. Pairwise sequence alignments showed SMV ORFI is highly conserved with other genogroup II noroviruses, and most closely related to GII strains Melksham and Hawaii virus. In addition, comparative sequence analyses indicated that SMV is likely a recombinant norovirus. VP1/VP2 proteins self-assembled into virus-like particles (VLPs) when expressed in insect cells by a recombinant baculovirus. Characterization of one clone that expressed VP1, but failed to assemble into VLPs, identified histidine residue 91 as important for particle assembly under standard conditions of expression.