Sequence and transcriptional analysis of terminal regions of the fowl adenovirus type 8 genome.

Fowl adenovirus (FAdV) type 1, CELO strain has no homologies to mastadenovirus E1A, E1B, E3 and E4, which regulate virus gene expression, DNA replication and virus-host interaction. Similarly, the right 5 kb and left 15 kb ends of CELO virus DNA are non-homologous to mastadenoviruses. To compare CELO virus with another FAdV, 7.5 kb of the left and 17 kb of the right ends of FAdV type 8 (strain A-2A) were sequenced and nine and 17 open reading frames (ORFs), respectively, were found. This FAdV-8 genome was similar to CELO virus in that (1) the central region contained the major structural protein genes including the fibre, pVIII, 100K, late 33K and pIVa2 genes, which were in the same order as in mastadenoviruses, (2) no homologues of mastadenovirus E1A, E1B, E3 and E4 were found in the ends, and (3) the left 6 kb and the right 13 kb ends showed no homology to mastadenoviruses. Several genomic features were unique to FAdV-8 compared to CELO virus. FAdV-8 contained one fibre gene in contrast to two in CELO virus. Three of eight unassigned ORFs in the left and five of 13 unassigned ORFs in the right ends were unique compared to CELO virus. Two sets of tandem repeats, one with five identical 33 bp repeats and the other with more than ten identical 135 bp repeats, mapped between 4.5 and 7.5 kb from the right terminus. No virus-associated RNA gene was found. Fifteen of 16 unique FAdV-8 ORFs tested were, as determined by RT-PCR, transcribed early.