Adenovirus helper function for growth of adeno-associated virus: effect of temperature-sensitive mutations in adenovirus early gene region 2.

Adeno-associated virus (AAV) grows efficiently only in cells that are also infected with an adenovirus (Ad). We employed Ad mutants to determine which genes may be required for the AAV helper function. Two mutants of Ad type 5 (Ad5), Ad5ts125 and Ad5ts107, with temperature-sensitive lesions in the E72 DNA-binding protein coded by the Ad early region 2, were deficient for AAV helper functions at the nonpermissive temperature (40 degrees C). In contrast, Ad5ts149, with a temperature-sensitive lesion in the Ad early region 5, was an efficient helper of AAV at the nonpermissive temperature. In KB cells, with the Ad5ts125 or Ad5ts107 mutant as the helper, the accumulation of AAV capsid proteins and AAV particles was decreased by about two logs, whereas AAV DNA synthesis was decreased only severalfold. Cytoplasmic, polyadenylic acid-containing AAV RNA is composed of a set of overlapping, spliced RNAs having different 5' start points. With the ts125 helper at 40 degrees C there was a decreased accumulation of some but not all of these AAV RNAs. The Ad5 E72 protein may have an effect on transcription or more likely posttranscriptional processing of AAV RNA. These observations suggest additional pleiotropic effects of the multifunctional E72 protein and suggest further similarities in the actions of E72 and the simian virus 40 T-antigen.