The early proteins of the nondefective Ad2-SV40 hybrid viruses: the 19K glycoprotein is coded by Ad2 early region 3

To determine which proteins are coded by early region 3 of Ad2, we compared Ad2-infected HeLa cells to cells infected with a series of nondefective Ad2-SV40 hybrid viruses (Ad2⁺ND) with progressively larger deletions of region 3. Both Ad2- and Ad2⁺ND-infected cells synthesized early proteins with apparent molecular weights of 72K, 16.5K, and 11K on sodium dodecyl sulfate- polyacrylamide gels. Ad2-infected cells contained, in addition, a 19K and a 17K glycoprotein and a 14K protein. None of the Ad2+ND-infected cells synthesized the 14K protein. Ad2⁺ND-infected cells also did not synthesize the 19K and 17K proteins, but cells infected with Ad2⁺ND₄, the ND with the smallest deletion in region 3, synthesized an 18K glycoprotein which had several methionine-containing peptides in common with the 19K and 17K proteins. We have, therefore, placed the genes for the 19K, 17K, and 14K proteins in early region 3. Two previous studies had assigned the 19K protein to early region 4 when in vitro translation of mRNA selected with restriction fragments from region 4 yielded a protein with an apparent molecular weight of 19K. However, our search of the literature revealed that the translation system used in those studies does not glycosylate proteins. Therefore, the 19K protein made in vitro was not glycosylated and could only have been the same protein as the 19K protein from infected cells if the glycosylated and nonglycosylated forms of the protein had the same molecular weight. By treating Ad2-infected cells with glucosamine or deoxyglucose we have determined that the nonglycosylated form of the 19K protein is a 15.5K protein.