Studies of Nondefective Adenovirus 2-Simian Virus 40 Hybrid Viruses III. Base Composition, Molecular Weight, and Conformation of the Ad2 + ND 1 Genome

Abstract

The nondefective adenovirus 2 (Ad2)-simian virus 40 (SV40) hybrid virus, Ad2 ⁺ ND ₁ , differs from the defective Ad-SV40 hybrid populations previously described, in that this hybrid virus can replicate without the aid of nonhybrid adenovirus helper. Consequently, the deoxyribonucleic acid (DNA) from this virus, which can be obtained free of nonhybrid adenovirus DNA, is well suited for biophysical studies on Ad-SV40 hybrid DNA. Such studies have been performed and demonstrate Ad2 ⁺ ND ₁ DNA to have a buoyant density (1.715 g/cm ³ ) and thermal denaturation profile (T _m = 75.1 C) almost identical with nonhybrid Ad2 DNA. Furthermore, its molecular weight, as determined by analytical zone sedimentation and electron microscopy, was 22 × 10 ⁶ to 25 × 10 ⁶ daltons, which is also very similar to that determined for Ad2. Electron micrographs showed all of the hybrid molecules to be double-stranded and linear. By using this determination of the molecular weight of Ad2 ⁺ ND ₁ DNA and assuming that 1% of this molecule consists of covalently linked SV40 DNA ( see companion paper ), we calculate that the hybrid DNA molecule contains 220 × 10 ³ to 250 × 10 ³ daltons of SV40 DNA, or the equivalent of one-tenth of the SV40 genome.