Biology Reference
In-Depth Information
with VP1 stability and FCV VP2 is essential for the production of
infectious virions.
6,7
The SaV GI, GIV, and GV genomes are predicted
to each contain three main ORFs, whereas the SaV GII and GIII
genomes (and RHDV genomes) each have only two main ORFs.
8
The SaV and RHDV ORF1 encode non-structural proteins and the
capsid protein. The SaV and RHDV ORF2 and SaV ORF3 encode
proteins of yet-unknown functions.
Genetic Analysis and Recombination
Human NoV can be divided into two genetically distinct genogroups
(GI and GII), which can be subdivided into at least 14 GI and 17 GII
clusters or genotypes.
9
Based on the capsid gene sequence, SaV can be
grouped into five distinct genogroups (GI to GV).
8
Human SaV
belong to GI, GII, GIV, and GV, whereas pig SaV belongs to GIII.
In both NoV and SaV, the genotypes are generally maintained across
the ORFs. However, a number of NoV and SaV strains failed to main-
tain their sequence identities for RdRp and VP1, and they were
shown to be recombinant.
10-16
Evidence suggested that the recombi-
nation site occurred at the polymerase and capsid junction on ORF1.
Phylogenetic analysis of the non-structural region (i.e. genome start to
capsid start) grouped these strains into one cluster, while the structural
region (i.e. capsid start to genome end) grouped these strains into two
distinct clusters. Figure 2 shows a possible mechanism for NoV and
SaV recombination.
10
Nucleotide sequence at the polymerase and cap-
sid junction generally is conserved among human NoV and SaV
strains,
14,17
likely facilitating a recombination event when nucleic acid
sequences of parental strains come into physical contact in infected
cells, e.g. during copy choice recombination. These data suggested
that these viruses could evade host immunity by readily changing their
structural region, i.e. the capsid protein that is immuno-reactive.
Expression in Insect Cells and Virus-like Particles
To date, all laboratory efforts to cultivate human NoV have failed,
18
but expression of the recombinant VP1 (rVP1) in insect or mammalian
