THE PRODUCT OF THE ADENOVIRUS INTERMEDIATE GENE-IX IS A TRANSCRIPTIONAL ACTIVATOR

Wt have investigated the functional properties of the product of the a denovirus type 5 gene IX. This gene, which is expressed at intermediat e times postinfection, encodes a small polypeptide (pIX) of 140 residu es that has previously been shown to be incorporated into the viral ca psid, Here, we show that pIX, in addition to its structural contributi on, exhibits transcriptional properties, In transient transfection exp eriments, expression of pIX stimulated adenovirus major late promoter. activity. The effect was independent of other viral proteins, but the level of promoter activation appeared strongly pIX dose dependent: si milar levels of induction were observed with other cellular or viral T ATA-containing (but not with TATA-less) promoters, This promoter speci ficity could be reproduced in a cell-free transcription system by the addition of pnrificd recombinant pIX, further stressing the transcript ional nature of the phenomenon, A preliminary structural analysis of p IX indicated that the integrity of a putative leucine zipper at the ca rboxy-terminal end of the molecule, as well as elements within the ami no-terminal half, was critical for pIX transcriptional activity. The r elevance of these findings in adenovirus infection is discussed.