SEQUENCE HETEROGENEITY OF HERON HEPATITIS-B VIRUS GENOMES DETERMINED BY FULL-LENGTH DNA AMPLIFICATION AND DIRECT SEQUENCING REVEALS NOVEL AND UNIQUE FEATURES
Hj. Netter et al., SEQUENCE HETEROGENEITY OF HERON HEPATITIS-B VIRUS GENOMES DETERMINED BY FULL-LENGTH DNA AMPLIFICATION AND DIRECT SEQUENCING REVEALS NOVEL AND UNIQUE FEATURES, Journal of General Virology, 78, 1997, pp. 1707-1718
So far, only a single heron hepatitis B virus genome (HHBV-4) has been
cloned and sequenced. Therefore, neither the significance of its sequ
ence divergence from other avian hepadnaviruses nor the sequence varia
bility of HHBV genomes in general are known. Here we have analysed the
sequence heterogeneity of HHBV genome populations in several sera fro
m naturally infected herons. A highly sensitive PCR method for full-le
ngth HHBV genome amplification was established which allowed direct se
quencing of entire HHBV populations without prior cloning. Sequences o
f HHBV genomes from four sera were thus obtained which differed from t
hose of HHBV-4 by upto 7%. Some of the divergent nucleotides and the c
orresponding amino acids of the predicted viral proteins were conserve
d in all four new HHBV isolates and varied only in HHBV-4. This indica
tes that the HHBV-4 genome is not in all aspects representative of thi
s class of viruses. Interestingly, a highly conserved ORF upstream of
the C-gene present in a position analogous to that of the mammalian he
padnavirus X-gene became apparent in all HHBV genomes. In contrast to
the duck hepadnaviruses, the small (sAg-S) instead of the largest (sAg
-L) envelope protein of all HHBVs has a myristylation site. These data
confirm the significant sequence divergence of HHBV from other avian
hepadnaviruses. Moreover, they show that HHBV has low sequence variabi
lity and indicate two new and unique features not evident in other avi
hepadnaviruses: an additional, highly conserved gene and potential myr
istylation of the sAg-S instead of the sAg-L envelope protein.