Characterization of bovine adenovirus type 3 E1 proteins and isolation of E1-expressing cell lines

Like human adenovirus type 5 (HAV5), bovine adenovirus type 3 (BAV3) early region 1 (E1) consists of E1A and E1B transcriptional units. In order to characterize BAV3 E1 proteins and to isolate a cell line of bovine origin that expresses BAV3 E1, polyclonal antibodies specific to E1A, E1B-157R, and E1B-420R were raised in rabbits. BAV3 E1A, E1B-157R, and E1B-420R were identified as 40, 17, and 47 kDa proteins, and had a half-life of 45-60 min, and 4-6 and 4-6 h, respectively. It appeared that E1A and E1B-157R were phosphorylated at the serine/threonine residues, whereas, E1B 420R was phosphorylated at both the serine/threonine and tyrosine residues. Three cell lines, MDBK-221 (Madin Darby bovine kidney (MDBK) transfected with BAV3 E1), FBK-34 (primary fetal bovine kidney (FBK) cells transfected BAV3 E1), and FBRT-HE1 (bovine fetal retinal (FBRT) cells transfected with HAV5 E1) were isolated and characterized for E1 expression. FBK-34 or FBRT-HE1 supported the replication of an E1A-deleted BAV3 (BAV3DeltaE1AE3) to approximately 1-2 x 10(8) PFU/ml, whereas, the virus titers in MDBK-221 were approximately 10(7) PFU/ml. These cell lines will be useful in generating and growing BAV3 E1-deleted recombinants, and also for studying E1 protein interactions with a number of cellular and/or viral proteins.