Transcription units of E1a, E1b and pIX regions of bovine adenovirus type 3

The major mRNA species in the E1 region of the genome of bovine adenovirus type 3 (BAV3) have been defined by using a combination of PCR, 5' RACE, Nor thern analysis and DNA sequencing, Independent transcription initiation sit es were identified for each of the E1a, E1b and protein IX (pIX) transcript ion units, but all mRNA species terminated at the same poly(A) addition sit e immediately downstream of the pIX open reading frame, Thus, the BAV3 E1 r egion, which consists of the E1a and E1b genes together with that for pIX, functions as a nested overlapping transcription unit. One major mRNA specie s encoding the flat protein was found and two mRNAs encoding E1b species, t he smaller of which encodes the E1b 17K protein alone and the larger encode s both 17 K and 47 K E1b proteins, were identified. One mRNA species encode s pIX. The E1 a transcript, encoding the predicted 214 residue E1a protein, has four exons. The smaller E1b mRNA has two exons, the second of which co rresponds to the last exon of E1a. No introns were detected in the larger E 1b mRNA that encodes both the E1b 17K and 47K proteins nor in the mRNA enco ding pIX. The relative times of appearance of the mRNAs from the E1-pIX gen e region following infection of bovine cells with BAV3 was determined.