THE E1 SEQUENCE OF BOVINE ADENOVIRUS TYPE 3 AND COMPLEMENTATION OF HUMAN ADENOVIRUS TYPE-5 E1A FUNCTION IN BOVINE CELLS

The bovine adenovirus type 3 (BAV3) genome was sequenced from the left end to the HindIII site at 11%. This region comprises the entire Fl t ranscription unit including the open reading frames (ORF) for proteins homologous to the E1A, E1B proteins and protein IX of human adenoviru s type 5 (Ad5). A portion of the BAV3 E1A protein showed significant h omology with conserved region 3 (CR3), the principal transactivation r egion of Ad5 E1A. The BAV3 E1A protein also contains a consensus seque nce known to be important for interaction with the cellular Rb protein but lacks most of the sequence corresponding to the second exon of Ad 5 E1A. Promoter sequences for BAV3 E1B were not defined though the rel evant region contains a 35-base pair repeat sequence. Two ORFs define the BAV3 E1B coding unit; one with regions homologous to sequences wit hin the Ad5 E1B 19k protein, and an overlapping ORF with significant h omology to the Ad5 E1B 55k protein. The encoded BAV3 E1B proteins of 1 57 and 420 amino acid residues (R) have predicted unmodified molecular weights of 17,393 and 46,734 respectively. Immediately following the E1B coding region there is a transcription unit containing an SP1 bind ing site and TATA box followed by an ORF which encodes a protein of 12 5R and predicted molecular weight of 13,706 with homology to protein I X of Ad5. Five concensus poly A addition sites are located in the 350 base pairs immediately following the protein IX coding region. The hom ology of sequences in the Ad5 E1A CR3 region and the corresponding BAV 3 protein suggested that the BAV3 protein could transactivate certain Ad5 genes normally transactivated by the Ad5 E1A product. Evidence for this hypothesis was obtained in studies in which bovine cells in cult ure were coinfected with BAV3 and a human adenovirus type 5 (Ad5) reco mbinant viral vector lacking the E1A region and having a lacZ reporter gene within the E3 region dependent on E1A for its expression. Coinfe ction resulted in the induction of beta-galactosidase activity and the increased expression of other Ad5 early (E2A 72k) and late (hexon) pr oteins.