Two functions encoded by adenovirus early region 1A are responsible for the activation and repression of the DNA‐binding protein gene.

Human adenovirus early region 1A (E1A) gene products differentially regulate the expression of early region 2A (E2A) encoding the DNA‐binding protein (DBP). In a microinjection system, plasmids containing the DBP gene associated with both its early (map coordinate 75) and late (coordinate 72) promoters, or only with the early promoter, are inefficiently expressed, and the presence of E1A DNA is required for full expression. In contrast, the E2A plasmid in which the DBP gene is associated solely with its late promoter, efficiently produces DBP, the synthesis of which is significantly inhibited by an E1A gene product. To identify which of the E1A products is responsible for either activation or repression of DBP gene expression, two E1A mutants (Ad5hr1 and Ad2/5pm975) have been tested in the microinjection system in the presence of different DBP plasmids containing either one or both promoters. The results obtained indicate that the product encoded by the E1A 13S mRNA is responsible for the stimulation of DBP produced from the early promoter and that the 12S mRNA codes for the product which represses the synthesis of DBP from the late promoter. These results were confirmed using clones in which the E2A early or late promoter was associated to the chloramphenicol acetyltransferase (CAT) gene and assayed for CAT activity after cell transfection in the absence or in the presence of wild‐type or mutant E1A plasmids, and we have also shown that this promoter‐dependent regulation is reflected in the relative amount of specific DBP mRNA.