A cascade of adenovirus early functions is required for expression of adeno-associated virus.

One measurable biological activity of early adenovirus genes is their ability to promote growth of the defective adeno-associated virus, AAV. We have identified an ordered sequence of communications among the early genes of adenovirus type 2 (Ad2) that results in expression of the helper activity. We purified DNA fragments and mRNAs corresponding to early Ad2 regions E1, E2A, E3 and E4 and injected them via glass capillaries into AAV-infected cells. DNAs were placed in the nucleus, mRNAs in the cytoplasm. AAV DNA and proteins synthesized in response to the injected Ad2 nucleic acids were extracted from as few as 100 cells and identified by gel electrophoresis. Our results reveal a cascade of early Ad2 gene regulation, E1 leads to E2A leads to E4, with E4 providing the helper effect for AAV.