Description of Adenoviridae
adapted from
ICTVdb
Virion Properties
Morphology
Virions consist of a
capsid, fibers, a core, and associated protein(s). Virus capsid
is not enveloped, round with icosahedral symmetry. The isometric
capsid has a diameter of 80-110 nm. The capsid shells of virions
are composed of a single layer. Capsids appear hexagonal in
outline. The capsid surface structure reveals a regular pattern
with distinctive features. The capsomer arrangement is clearly
visible. The capsid consists of 252 capsomers; 12 of which are
pentons; 240 are hexons; each capsomer measures 8-10 nm in
diameter. Surface projections are distinct, one or two filaments;
protruding from the 12 vertices. Hexons; consist of a hexagonal
base with a central cavity. Penton bases are tightly associated
with one or two fibers; fiber proteins interact to form a shaft
of characteristic length with a distal knob. The length of fibers
is between 9-77.5 nm. The core consists of a nucleoprotein
complex.
Physicochemical and Physical Properties
The molecular mass (Mr) of
virions is 150-180 x 10
6. Virions have a buoyant
density in CsCl of 1.32-1.35 g cm
-3. The thermal
inactivation point (TIP) is at 56°C. Under
in vitro
conditions virions are stable when stored at -20°C; stable
in acid environment of pH 5-6. Virions are not sensitive to
treatment with lipid solvents.
Nucleic Acid
The genome is not segmented and contains a single
molecule of linear double-stranded DNA. The complete genome is
35800-36200 nucleotides long. The genome has a guanine + cytosine
content of 48-61% for
Mastadenovirus and 54-55% for
Aviadenovirus 55 %. The genome has terminally redundant
sequences. The terminally redundant sequences have inverted
terminal repetitions (ITR) (103bp for human adenovirus 2, ITR's
between 50-200 bp found in all viruses so far analyzed). The
genome has a virus coded terminal protein which is covalently
linked to the 5'-end of each DNA strand.
Replication is divided into EARLY and LATE phases, the latter
defined as beginning with the onset of DNA replication.
Attachment to cells is rather slow, taking several hours to reach
a maximum.
Genome Organization and Replication
Virions attach fibers to enter host cells by endocytosis.
The process of intracellular uncoating of virions is
understood. Virus uncoating occurs in the cytoplasm; the viral
core is delivered to the cell nucleus; the site of mRNA
transcription or DNA replication.
By itself, genomic nucleic acid is infectious.
Infection and
Replication: Host cell DNA synthesis is shut-off; early
in the replication cycle. Host cell RNA and protein synthesis is
shut-off; later in the replication cycle.
Transcription: Virus
transcription is temporally regulated; 2 classes of genes
recognized; they are termed EIA and E1B; E2A and E2B; E3 and E4
early and late (L1, L2 and L3; L4 and L5). The viral genome is
transcribed from both DNA strands by host cell enzymes.
During the early stage, the viral genome is transcribed by
eukaryotic nuclear RNA polymerase II; late stage, the viral
genome is transcribed by eukaryotic nuclear RNA polymerase III.
Cellular RNA polymerase III; encode products which facilitate
translation; of late mRNAs. Viral genes are expressed from an
early promoter (that is E1-E4, two intermediate), or a later
promoter (L). Viral mRNA(s) is/are transcribed from four early
E1-E4, two intermediate promoters and one major late (L) promoter
5 promoter(s, in an ambisense coding arrangement; all.
Primary transcripts are capped; polyadenylated. Viral mRNA
families are produced by complex splicing patterns.
Coding Strategy of Segment 1:
sequence encodes non-structural proteins. Sequence encodes
protease.
Translation: Structural
proteins, or non-structural proteins. Synthesized in the nucleus.
Translation of structural proteins occurs during the early
transcription phase of replication (TP), or intermediate
transcription phase of replication (IX and IVa2), or late
transcription phase of replication (II-VIII, X). Translation of
non-structural proteins occur in the early stage of replication
(DBP DNA pol and others), or late stage of replication
(maturation 52/55kDA, mu, 33kDa p protein and 100 kDa).
Structural proteins, or non-structural proteins (many). Are
modified by post-translational processes. Including proteolytic
cleavage, or phosphorylation, or glycosylation.
The genome replicates in the nucleus. Replication does not
involve a reverse transcription step. Genome replication occurs
by a strand-displacement. Genome replication uses a protein
priming mechanism (terminal protein) (together with a), or
virus-coded DNA polymerase (and), or DNA binding protein (in
concert with), or cellular factors.
Virions may provide helper functions to dependent virus during
replication. Virion acts as helper for a satellite virus.
Replication cycle The
precursor of capsid protein is found in the infected cell
nucleus. Viral proteins accumulate in the nucleus. Virions
accumulate in the cell nucleus.
Assembly and Egress:
Viruses assemble in the nucleus (sometimes in paracrystalline
arrays along with similar arrays of virus structural
proteins).
Maturation: Virions
mature after proteolysis of some structural proteins by the
virus-coded protease.
Release: Virus is
released from host cell. Virus is released from host cell by
disintegration.