Expression of Early Adenovirus Genes Requires a Viral Encoded Acidic Polypeptide

Host-range mutants of adenovirus 5 that contain a defect in region E1A (0-4.5 units) fail to replicate in HeLa cells and to transform rodent cells. In HeLa cells, these mutants synthesize only the two RNAs from E1A that share the same 5′and 3′termini but differ in length by the amount of internal sequence removed by splicing. RNA from wild-type virus, selected by hybridization to DNA from region E1A, translates into polypeptides of Mr51,000 and 48,000 that are highly acidic in isoelectric focusing gels. These acidic Mr51,000 and Mr48,000 polypeptides are encoded by the longer and shorter E1A RNAs, respectively. Two of the host-range mutants, H5hr1 and H5hr2, fail to synthesize the Mr51,000 polypeptide but do produce the Mr48,000 polypeptide and a novel polypeptide thought to be a truncated portion of the Mr51,000 polypeptide. H5hr1 and H5hr2 are hypothesized to have termination codons in sequences found only in RNA encoding the Mr51,000 polypeptide. This prediction is verified for H5hr1 by DNA sequence analysis. The other three hostrange mutants (H5hr3-5) synthesize both acidic polypeptides and are predicted to be missense. These results strongly imply that the Mr51,000 polypeptide, alone or in combination with the Mr48,000 polypeptide, is needed to regulate expression of adjacent viral genes during the early phase of adenovirus infection.