A nonessential glycoprotein is coded by early region E3 of adenovirus type 7

The E3s of both Ad7 (group B) and Ad2 (group C) encode glycoproteins that are similar in apparent molecular weight, that have high-mannose oligosaccharides, and that are nonessential for virus growth on cultured KB cells.

Abstract

Ad7 was shown to induce polypeptides of 66,000 daltons (66K), 28K, and 16K during early stages of infection. The 28K could be labeled with [2-3H]mannose and it bound to concanavalin A-agarose, indicating that it is a glycoprotein. Neither the glycoprotein nor the 16K polypeptide were induced by a viable early region E3 deletion mutant or an E3 insertion mutant, indicating that the polypeptides are coded by early region E3, and that they are nonessential for growth of Ad7 on cultured KB cells. The Ad7 glycoprotein was compared to the Ad2 E3-coded glycoprotein in terms of size and oligosaccharide linkage. The Ad7 glycoprotein has an apparent molecular weight of 28K versus 25K for the Ad2 glycoprotein, as estimated by SDS-PAGE. The Ad7 glycoprotein and the purified 25K Ad2 glycoprotein were digested with endo-β-acetylglucosaminidase H (endo H) to determine the type of oligosaccharide linkages as well as the apparent molecular weights of the polypeptide chains. Endo H reduced the apparent molecular weights of the Ad7 and Ad2 glycopolypeptides from 28K and 25K, to 17.5K and 19K, respectively. This establishes that both proteins have Asn-linked oligosaccharides of the high-mannose type, and that the Ad7 polypeptide chain is slightly smaller than that of Ad2, 17.5K versus 19K. Thus, the E3s of both Ad7 (group B) and Ad2 (group C) encode glycoproteins that are similar in apparent molecular weight, that have high-mannose oligosaccharides, and that are nonessential for virus growth on cultured KB cells.