Transcription mapping and characterization of 284R and 121R proteins produced from early region 3 of bovine adenovirus type 3

We established the transcription map of early region (E) 3 of bovine adenov irus 3 (BAV-3) by Northern blot, S1 nuclease protection assays, cDNA sequen cing, and RT-PCR analysis. Five major classes of mRNAs were identified, whi ch shared the 3 ' ends. Four classes of mRNAs transcribed from the E3 promo ter also shared the 5 ' end, while one major class of mRNA transcribed from the major late promoter contained a tripartite leader sequence at the 5 ' end. These five transcripts have the potential to encode four proteins. nam ely 284R, 121R, 86R, and 82R. To identify the proteins, rabbit antiserum wa s prepared using a bacterial fusion protein encoding 284R or 121R protein. Serum against 284R immunoprecipitated protein of 26-32 kDa in in vitro tran slated and transcribed mRNA and three proteins of 48, 67, and 125 kDa from BAV-3-infected cells. Western blots and enzymatic digestions confirmed that the 284R protein is a glycoprotein, which contains only N-linked oligosacc harides, both high mannose (48 kDa) and complex types (67 kDa). Serum again st 121R immunoprecipitated a protein of 14.5 kDa from in vitro translated a nd transcribed mRNA and BAV-3-infected cells. Although 121R protein shows l imited sequence similarity to a 14.7-kDa protein of human adenovirus 5, the 284R protein appears to be unique to BAV-3. Since proteins encoded by the E3 region appear to influence adenovirus pathogenesis, the 284R protein may contribute to the unique pathogenic properties or BAV-3, (C) 1999 Academic Press.