Biology Reference
In-Depth Information
juveniles. Once again, Asian scientists tend to use VNN to describe
the disease symptom, while Western scientists tend to use VER. The
concept differences between names may be clarified by whether the
nerve cells are affected, which has yet to be confirmed by any firm
evidence.
Genome of Fish Nodavirus
The genome of the nodaviruses is bipartite of single-stranded, positive-
sense RNAs: RNA1 assumedly encodes the viral replicase, whereas
RNA2 encodes the capsid protein. The complete sequence of RNA1
and RNA2 of striped jack nervous necrosis virus (SJNNV) was deter-
mined in 1995 and 1999, respectively, while we completed the RNA2
of grouper NNV in 1999 and RNA1 in 2001. The sequences of
RNA2 of
Dicentrarchus labrax
encephalitis virus (DlEV) and Atlantic
halibut virus (AHV) (Grotmol
et al.,
2000) were also determined.
RNA2 of MGNNV and DGNNV, two grouper nervous necro-
sis viruses isolated from Taiwanese
Epinephelus malabaricus
and
Epineph-
elus lanceolatus,
respectively, was cloned and sequenced using standard
procedures (Lu and Lin, 1999).
3
Both RNAs were 1390 nucleotides
(nt) long and contained a single open reading frame (ORF) encoding a
338-amino-acid protein of approximately 37 kDa, the putative capsid
protein. The ORF spanned nt 15-1031, leaving an untranslated region
of 14 nt at the 5´-end and 359 nt at the 3´-end. Alignment of the two
sequences showed that they were 99% identical at both the nucleotide
level and the amino acid level. Comparison with the recently deter-
mined sequence of RNA2 from the grouper virus GGNNV indicated
that the RNA2 of MGNNV and DGNNV contained shorter 5´ and 3´
non-coding regions. This may be due to the absence of authentic 5´ and
3´ termini in the MGNNV and DGNNV clones, which were generated
with primers based on the 5´- and 3´-end sequences of SJNNV RNA2.
Despite the discrepancy in length, RNA2 of all three grouper viruses
contained an ORF encoding a protein of 338 amino acids.
Based upon T4-region sequences from more than 20 other betan-
odavirus RNA2 segments, Nishizawa
et al.
(1997) classified the betan-
odaviruses into four groups: SJNNV, tiger puffer NNV (TPNNV),
barfin flounder NNV (BFNNV), and red grouper NNV (RGNNV).
