Biology Reference
In-Depth Information
motifs upstream from the protease coding region, which show sequence
similarity to pestivirus RNA helicase sequences, have recently been
mapped by computational tools.
17
Upon infection, two large nonstructural proteins are translated
from the genomic RNA: nsP1a and nsP1a1b. These proteins mature
by proteolysis involving both the viral protease and cellular proteases,
and give rise to the viral proteins implicated in the transcription of a
full-length negative-strand RNA molecule (antigenomic RNA). It is
believed that this RNA molecule serves as a template for the tran-
scription of both the new full-length 6.8 kb-genomic and the ORF2-
containing 2.4 kb-subgenomic RNA molecule.
19
Translation of this
subgenomic RNA is used to produce large amounts of structural pro-
teins for the efficient assembly of the progeny viruses.
15
Both astro-
virus genome organization and replication/translation strategies have
frequently been compared to those of alphaviruses and caliciviruses
due to their similarities.
This review will focus on recent advances in the understanding of
the molecular biology, structure, and replication cycle of HAstV.
Current efforts are being undertaken to complete the characterization
of their genomic organization, to study virion assembly and morpho-
genesis, and to understand the relationships between the virus and the
host immune response. Major developments on these issues are
expected in the near future.
Molecular Virology and Replication Cycle:
New Insights
Structural Proteins
Considerable progress has been made in understanding the basics of
HAstV genomic organization; however, capsid protein processing and
assembly, as well as genome encapsidation, are not yet clear. Translation
of the structural polyprotein from ORF2 (782 to 794 amino acids,
depending on serotype) most likely occurs from the subgenomic
RNA. The presence of a conserved RNA sequence upstream from the
ORF2 initiation codon with a possible role in the regulation of the
