EIa-mediated stimulation of the adenovirus EIII promoter involves an enhancer element within the nearby EIIa promoter

The transcriptional induction of adenovirus early genes by the viral immediate early gene EIa constitutes an attractive model system for the study of control mechanisms involved in eucaryotic promoter function. The EIa-mediated activation of the divergently transcribed EIIa early (EIIaE) and EIII promoters was investigated in experiments in which recombinant plasmids containing the entire EIIa-EIII control region were cotransfected with a plasmid expressing the EIa 13S mRNA. First, both promoters were activated by low levels of EIa, but the extent of EIII induction decreased with increasing EIa concentrations, whereas EIIaE stimulation remained unchanged. Second, transcriptional analysis of deletion mutants revealed that an element of the EIIaE promoter contributed to maximal EIa responsiveness of the nearby EIII promoter. This element, located between positions -82 and -71 with respect to the EIIaE major cap site, corresponded to the central portion of an EIa-dependent enhancer, originally mapped between about -110 and -50 (P. Jalinot and C. Kédinger, Nucleic Acids Res. 14:2651-2669, 1986). The implication of these observations in the coordinate expression from the EIIaE and EIII promoters during lytic infection is discussed.