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Morphology and virus structure involved in nuclear localization (RKRP) and penton base interac-
Adenoviruses are non-enveloped with an icosahedral capsid tions (VYPF) are conserved among aviadenoviruses (Grgić et al.,
and diameters of 70–90 nm. The relative molecular mass (Mr) 2014). VYPF motif is also found in the EDSV fibre protein (Hess
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of the virion is 150–180 × 10 and the buoyant density in CsCl et al., 1997). RKRP and VYPF motifs are equivalent to mastad-
is 1.31–1.36 g/cm (Harrach et al., 2011; Berk, 2013). Studies enovirus KRAR and VYPY, respectively (Grgić et al., 2014).
3
from our laboratory show that the buoyant density of FAdV-9 is The fibre protein is trimeric as a result of interaction of three
3
1.33 g/cm (J. Ackford, personal communication). Most struc- IV polypeptides. These interactions form a shaft of characteris-
tural studies have been conducted in human adenoviruses types tic length with a distal knob. Avian adenoviruses have one or
2 and 5 (HAdV-2 and HAdV-5). Structural proteins of TAdV-3, two fibre proteins per vertex. Avian adenoviruses such as EDSV
FAdVs and EDSV have been characterized by SDS-PAGE (Todd (genus Atadenovirus) and TAdV-3 (genus Siadenovirus) have
and McNulty, 1978; van den Hurk, 1992). Virions consist of a one fibre protein per vertex (Gelderblom and Maichle-Lauppe,
capsid surrounding the core – viral genome and associated pro- 1982; van den Hurk, 1992). FAdVs, and most likely all mem-
teins (Fig. 10.1A) (Berk, 2013). The viral capsid consists of 240 bers of the genus Aviadenovirus, possess two fibres per vertex
hexon capsomers (protein II, 8–19 nm in diameter), 12 penton as demonstrated by electron microscopy (EM) and structural
bases (protein III) and one or two fibre proteins (protein IV) per analysis (Gelderblom and Maichle-Lauppe, 1982; Hess et al.,
vertex. Serotype-specific determinants are located on both, the 1995). Except for FAdV-1, EM analysis shows nearly similar
fibre and the hexon. length within the fibre pair in the rest of the FAdV serotypes
The hexon protein consists of conserved pedestal regions P1 (Gelderblom and Maichle-Lauppe, 1982). Consistent with the
and P2 and the variable loops L1–L4. L1, L2 and L4 regions are EM analysis, FAdV-1 possess two genes that encode the fibre
located at the surface of the hexon protein and thus determine proteins with marked differences in length (Chiocca et al.,
adenovirus immunogenicity and neutralization (Roberts et al., 1996). Similarly, though not yet characterized by EM, other
1986). The L1 region has been extensively used for genotyping, aviadenoviruses, such as pigeon adenovirus 1 (PiAdV-1) and
phylogenetic studies and potential diagnosis of FAdVs using vari- turkey adenovirus 5 (TAdV-5), also possess two genes encoding
ous molecular approaches (Raue and Hess, 1998; ; Meulemans et fibre proteins with marked differences in length (Marek et al.,
al., 2004; Marek et al., 2010a; Pizzuto et al., 2010). 2014a,b). Consistent with the EM studies, FAdV-4, and probably
The fibres of all analysed adenoviruses range between 9 to FAdV-10, possesses two fibre genes that encode fibre proteins
77.5 nm in length (Harrach et al., 2011). The fibres of avian ade- (432 and 474 amino acids in fibres 1 and 2, respectively) (Griffin
noviruses analysed by electron microscopy (EM), including long and Nagy, 2011) with subtle differences in length (Gelderblom
and short fibres of aviadenoviruses, range between 11 to 46.8 nm and Maichle-Lauppe, 1982). Other aviadenoviruses that have
in length. The longest fibres are found in FAdV-1 (long fibre, not been characterized by EM and also possess two genes encod-
46.5–46.8 nm) and EDSV (41.7 nm), whilst the shortest fibres ing fibres with nearly similar lengths include goose adenovirus 4
are found in members of species FAdV-C (16.5–16.6 nm) and (GoAdV-4) and TAdV-1 (Kaján et al., 2012). Aviadenoviruses
TAdV-3 (17 nm) (Gelderblom and Maichle-Lauppe, 1982; van including members of species FAdV-B, FAdV-D and FAdV-E,
den Hurk, 1992). In general, the motifs present in the fibre tails TAdV-4 and duck adenovirus 2 (DAdV-2) have one fibre gene in

(A) (B)

Figure 10.1 (A) Structural proteins in the virus coat and core (reprinted from Nemerow, G.R., Pache, L., Reddy, V., Stewart, P.L. Virology, 2009;
384: 380–388, with permission from Elsevier). (B) Negatively stained fowl adenovirus 9 particles, showing the characteristic morphology of
adenoviruses (courtesy of James Ackford, Department of Pathobiology, University of Guelph).