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Avian Adenovirus | 295

adenovirus E4ORF6-like genes such as DAdV-1 E4 and aviad- the wild-type virus, seroconversion is significantly decreased
enovirus ORFs 24 and 14 may block p53-induced apoptosis. (Le Goff et al., 2005). It remains unknown whether FAdV-1
Adenovirus infection stimulates the host DNA damage ORFs 9, 10 and 11 are functional equivalents to mastadenovirus
response (DDR) as a consequence of viral genome replication. E3 proteins. FAdV-9 ORF1C has 36.8% amino acid identity to
The DDR is regulated by the phosphatidylinositol 3-kinase-like the E5 oncoprotein of bovine papillomavirus type 1 (Ojkic and
protein kinase family, including ataxia-telangiectasia mutated Nagy, 2000) and is predicted to down-regulate MHC-I molecules
(ATM) and ATM- and Rad3-related (ATR). DDR leads to cell during infection (Corredor and Nagy, 2010a).
cycle arrest and apoptosis. Mastadenovirus E4orf4 protein, in
concert with the cellular PP2A, reduces phosphorylation of ATM
and ATR and interferes with DDR signalling to favour virus repli- Genome structure and organization
cation (Brestovitsky et al., 2016). The mechanisms whereby avian Adenoviruses have a linear dsDNA as a genome whose size ranges
adenoviruses counteract DDR signalling remain undetermined. from 26,163 to 48,395 bps with 33.6 to 66.9% G + C content. In
Mastadenovirus E3 proteins are known to counteract the host general, the genome is covalently linked to the viral terminal pro-
antiviral response (Hansen and Bouvier, 2009). Mastadenovi- tein (TP) at the 5′ ends and consists of inverted terminal repeats
rus E3–14.7 kDa inhibits the NF-κB-induced transcription of (ITRs, 36–371 bp), early (E) gene clusters and a late (L) gene
inflammatory genes, whereas TNF-α and FAS ligand signalling is transcriptional unit.
inhibited by the viral E3-10.4 kDa/14.5 kDa proteins. The E3-19K To date, the whole nucleotide sequence of members rep-
glycoprotein retargets MHC-I molecules to the endoplasmic resenting each genus is available, except for the white sturgeon
reticulum to prevent peptide presentation (Thaci et al., 2011). adenovirus 1 (WAdV-1) genome (Harrach et al., 2011). Genome
Homologues to the mastadenovirus E3 19K gene are not found sequence data have provided further understanding of gene
in avian adenoviruses. FAdV-1 ORFs 9, 10 and 11 are predicted organization and evolutionary relationships among all adenovi-
to be type-1 transmembrane glycoproteins with Ig-like domains, rus genera.
as described for mastadenovirus E3 19K protein (Washietl and Fig. 10.6 illustrates the genome organization among genera. In
Eisenhaber, 2003). Deletion mutant FAdV-1 lacking these ORFs general, gene arrangement in the central region of the adenovirus
replicates slower in vivo, and, relative to chickens inoculated with genome, containing the E2 and L genes, is well conserved among

Mastadenovirus (Human adenovirus 2)

E1 region E3 region
E1B E1B 33 K
55k pX 22 K
E1A 19k IX pVII pVI Protease
VA 52K pIIIa III V hexon 100 K pVIII Fiber
pTP’
IVa2 pTP Pol’
pol DBP UXP’ UXP’’ 6/ 4 dUTPase
UXP 7 34 k 2
Aviadenovirus (Fowl adenovirus 9)
52K pVII pVI 33 K
ORFs 0, 1, 1A, 1B, 1C, 2 pX hexon Protease 100 K 22 K pVIII
pIIIa III Fiber Fiber Gam-1 11 25R
’ TR-1 TR-2
IVa2 pol pTP pTP’ DBP U-exon 22 20 19 17 23
ORFs 24, 14, 13, 12 20A
Atadenovirus (Ovine adenovirus 7)
LH region pIIIa pVII pVI Protease 33 K Fiber
E1B 55K III pX hexon 100 K 22 K pVIII
52 K
p32K
IVa2 pol pTP pTP’ DBP U exon 34 K E4.1 5 2
34 K 6 4 1
RH region
Siadenovirus (Frog adenovirus 1)
pVII 33 K pVIII
Hydrophobic pIIIa III pX 22 K E3
Sialidase 52 K pVI hexon Protease 100 K Fiber 7

IVa2 pol pTP pTP’ DBP U exon 8
10,000 20,000 30,000 40,000 bp
Figure 6. Genome organization among adenovirus genera (From Harrach, B., Benko,̈ M., Both, G.W., Brown, M., Davison, A J,
Echavarría, M., Hess, M., Jones, M.S., Kajon, A., Lehmkuhl, H.D., Mautner, V., Mittal, S,K., Wadell, G. Ninth Report of the
Figure 10.6 Genome organization among adenovirus genera (from Harrach, B., Benkö, M., Both, G.W., Brown, M., Davison, A J, Echavarría,
International Committee on Taxonomy of Viruses. 2012 with modifications.)
M., Hess, M., Jones, M.S., Kajon, A., Lehmkuhl, H.D., Mautner, V., Mittal, S,K., Wadell, G. Ninth Report of the International Committee on
Taxonomy of Viruses, 2011, with modifications).