Functional diversity of E1A gene autoregulation among human adenoviruses

Autoregulation of the adenovirus E1A gene involves its constitutive expression and positively and negatively regulated transcription. Dissection of this process will identify basal-level cis elements and autoregulatory targets of the E1A promoter and functional domains within the trans-acting E1A gene products. In this report, the DNA sequence of the human subgroup B adenovirus type 3 (Ad3) E1A gene is presented and compared with that of the E1A genes of similar and distantly related human adenoviruses. The cDNA forms of the Ad3 E1A gene, corresponding to two major early mRNA species, are cloned, sequenced, and subcloned into plasmid expression vectors. Cotransfections of cell cultures are performed with Ad5 or Ad3 E1A gene expression plasmids and a reporter gene under control of the Ad5 or Ad3 E1A promoter. The Ad5 and Ad3 E1A promoters are similarly repressed by either serotype's 12S cDNA gene products. The Ad3 E1A promoter responds much more strongly than the Ad5 E1A promoter to transactivation by 13S cDNA gene products. In contrast, the 13S cDNA gene of Ad5 has greater transactivation activity than that of Ad3. Experiments with missense mutations of the Ad5 E1A gene indicate that transactivation of the Ad5 E1A promoter is weak, just reversing or balancing negative autorepression. Single amino acid substitutions in the conserved, repressive functional domain 2 of the E1A gene modulate transactivating activity that is usually associated with the separate and distal conserved functional domain 3. These results suggest a strong structure-function relationship influenced by the variable sequences separating these conserved domains.