Arch Virol (2005) 150: 2529–2538
Deletion analysis of the sapovirus VP1 gene
for the assembly of virus-like particles
G. S. Hansman, N. Matsubara, T. Oka, S. Ogawa, K. Natori,
N. Takeda, and K. Katayama
Department of Virology II, National Institute of Infectious Diseases,
Received February 1, 2005; accepted May 19, 2005
Published online August 1, 2005
Summary. Human sapovirus (SaV) strains are agents of gastroenteritis. They
cannot be grown in cell culture. In this study, constructs containing SaV N-
and C-terminal-deleted recombinant capsid proteins (rVP1) were expressed in
a baculovirus expression system to allow us to better understand the sequence
requirements for the formation of virus-like particles (VLPs). Only proteins de-
rived from N-terminal-deleted rVP1 constructs that began 49 nucleotides down-
stream assembled into VLPs, which included both small and native-size VLPs.
Our results were similar to those reported in a rabbit hemorrhagic disease virus
(RHDV) N- and C-terminal-deleted rVP1 expression study but were distinct from
those reported in a norovirus N- and C-terminal-deleted rVP1 expression study,
suggesting that SaV and RHDV may have similar expression requirements.
The family Caliciviridae contains four genera, Sapovirus, Norovirus, Lagovirus,
and Vesivirus, which include sapovirus (SaV), norovirus (NoV), rabbit hemor-
rhagic disease virus (RHDV), and feline calicivirus (FCV) strains, respectively.
Despite the fact that strains from these four genera are genetically and antigenically
distinct, some characteristics are common. For example, the major capsid gene
of SaV and RHDV is fused to the non-structural genes on open reading frame
1 (ORF1), whereas the major capsid gene of NoV and FCV is located on a
separate ORF (ORF2). This suggests that SaV/ RHDV and NoV/ FCV have similar
proteolytic processing or expression characteristics, respectively.
SaV strains can be divided into ﬁve genogroups (GI-GV), of which GI, GII,
GIV, and GV strains infect humans, while GIII strains infect porcine species. The
SaV GI, GIV, and GV genomes are predicted to each contain three main ORFs,