PRODUCT OF THE ADENOVIRUS INTERMEDIATE GENE IVA2 IS A TRANSCRIPTIONALACTIVATOR OF THE MAJOR LATE PROMOTER

During the course of lytic infection, the adenovirus major late promot er (MLP) is induced to high levels after replication of viral DNA has started. We had previously shown that sequence elements located downst ream df the MLP start site were implicated in this late-specific trans criptional activation (DE1, between +85 and +98; DE2, between +100 and +120). Two positive transcription factors involved in this activation have been detected. DEF-A, which specifically binds to DE1 and also t o the 3' portion of DE2 (DE2a), and DEF-B, which interacts with the 5' part of DE2 (DE2b). When present together, these two proteins coopera tively assemble onto the DE2 element. We now report the purification o f DEF-B and show that it is identical to the product of the adenovirus IVa2 gene product. This conclusion is based on microsequence analysis of DEF-B as well as on the inhibitory effect of antibodies against IV a2 on the DNA-binding activity of DEF-B and also on DE-dependent in vi tro transcription. In addition, we show that bacterially synthesized I Va2 protein binds to the DE sequences with the same specificity as DEF -B. Finally, in transfected cells, a recombinant IVa2 protein stimulat es MLP activity in a DE-dependent fashion. The physiological implicati ons of these findings are discussed.