Biology Reference
In-Depth Information
The 5
UTR of 324-341 nucleotides contains an IRES element that
is required for the cap-independent translation of the viral genomic
RNA; a 3
′
-UTR of about 200 nucleotides is required for viral genome
replication. The coding region encodes the core, envelope 1 and 2
structural proteins, and the p7, NS2, NS3, NS4A, NS4B, NS5A, and
NS5B nonstructural proteins (Fig. 1c). The core protein can bind to
RNA to encapsidate the HCV genome. The envelope proteins E1 and
E2 form a heterodimer that makes up the viral envelope. The NS3
protein has serine protease and helicase activities, while the NS4A
protein functions as a cofactor for the NS3 protease activity.
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The
function of NS4B is unknown. The NS5 region encodes NS5A and
NS5B, of which the former is believed to play a role in RNA replica-
tion, while the latter has an RNA-dependent RNA polymerase activ-
ity.
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The NS5A protein also has an interferon sensitivity
determination region (ISDR), and mutations within this region
determine the efficacy of interferon
′
α
therapy for HCV infection.
Hepatitis D Virus
Hepatitis D virus (HDV) has a 1700-nucleotide single-stranded RNA
genome that encodes the only HDV protein, called the hepatitis delta
antigen (HDAg). This protein is expressed in large and small forms,
and these are involved in structural as well as regulatory functions.
HDV is a replication defective virus that requires the HBV helper
function in the form of HBsAg to envelope the HDAg/HDV RNA
core particle. The HDV envelope contains all three forms (S, M, and
L) of HBsAg, with a predominance of the major (small) form of
HBsAg. The nucleocapsid structure of HDV is composed of the viral
single-stranded RNA genome and about 60 copies of delta antigen in
its large and small forms.
Hepatitis E Virus
Hepatitis E virus (HEV) is a spherical, non-enveloped, RNA virus
with a positive sense RNA genome of ~7.2 kb that encodes three
overlapping open reading frames (ORFs). ORF1 (~5 kb) encodes the
