| The fowl adenovirus 9 (FAdV-9) genome was sequenced and found to be 45,063 nucleotides in length, the longest adenovirus (AdV) genome whose complete nucleotide sequence has been reported so far. No regions homologous to early regions 1, 3 and 4 of mastadenoviruses were recognized. Gene homologues for early region 2 proteins, intermediate protein IVa2 and late proteins were found by their similarities to protein sequences from other AdVs. Two regions of repeated sequences were identified in the FAdV-9 genome. The shorter repeat region (TR-1) contained 5 identical and contiguous direct repeats that were each 33 by long, while the longer repeat region (TR-2) consisted of 13 identical and contiguous, 135 by long repeated subunits.; Sequence analysis of cDNAs representing selected early proteins identified untranslated leader sequences, precise locations of splice donor and acceptor sites as well as polyadenylation signals and polyadenylation sites. Expression of the major late transcriptional unit involved complex differential splicing and polyadenylation to give 6 families of late mRNAs and had several unique features. For example: late transcripts contained bipartite leader sequences, whereas late mRNAs from mastadenoviruses contain a tripartite leader. As well, the splicing patterns were more complex for some FAdV-9 late transcripts (pIII, pVII, pX, 100K, fiber) compared to corresponding mRNAs from mammalian AdVs.; An infectious FAdV-9 genomic clone was constructed by homologous recombination in Escherichia coli. A recombinant virus, in which the TR-2 was replaced by the enhanced green fluorescence protein (EGFP) coding sequence as a marker, was generated indicating that the TR-2 was non-essential and that foreign DNA could be inserted in that site. In vivo characterization of the recombinant and parental viruses was performed by PCR, to examine their distribution in experimentally infected chickens, and by ELISA, to evaluate antibody responses. The deletion of TR-2 did not significantly influence the immune response and the tissue distribution of the recombinant and parental viruses were similar. From the data it was concluded that TR-2 was dispensable for FAdV-9 replication both in vitro and in vivo. |
