cis-dominant defect in activation of adenovirus type 5 E1b early RNA synthesis.

A cis-dominant mutation in the adjacent E1a gene disrupted the accumulation of adenovirus type 5 E1b mRNA during the early phase of infection. Steady-state levels of cytoplasmic and nuclear E1b RNAs in cells infected with dl312, a strain that lacks the E1a TATA box, cap site, and much of the coding sequence, were reduced 5- to 10-fold even when the E1a activator was provided in trans. The strain was defective for early E1b RNA synthesis but not for E1b RNA made late or during prolonged incubation in the presence of an inhibitor of DNA replication. The defect in E1b RNA synthesis could not be attributed to the E1a promoter sequences missing in dl312 DNA. If the E1a protein-coding region contains cis-acting regulatory sequences, they are not part of the previously mapped E1b transcriptional control region and may represent additional regulatory elements that ensure prompt and efficient E1b expression during the early phase of infection.