Adenoviruses are nonenveloped icosahedral-shaped particles. The double
stranded viral DNA genome contains four major early transcription uni
ts, designated E1 (a and b), E2 (a and b), E3 and E4, which are expres
sed in a regulated manner soon after infection. The gene products of t
he region E3, shown to be nonessential for viral replication in vitro,
are believed to be involved in counteracting host immunosurveillance.
Human adenovirus type 5 DNA sequences of transcription units L4 and L
5 adjacent to E3 were used to localize E3 within the bovine adenovirus
type 2. The DNA sequences between 74.8 and 84.4 mu containing E3 and
the fiber gene were determined. The E3 region was found to consist of
about 2.3 kb pairs and to encode four proteins longer than 60 amino ac
ids. However, these four open reading frames did not show significant
homology to any other known adenovirus DNA or protein sequence.