Adenovirus DNA. I. Molecular weight and conformation.

Abstract

The intact DNA molecules isolated from 6 different human adenovirions, including the "highly" carcinogenic adenoviruses (Ad) 12 and 18, the "weakly" carcinogenic Ad 7 and 21, and the noncarcinogenic Ad 2 and 4 were studied. In all cases the molecules are linear, 11 to 13 u in length, as seen by protein-film electron microscopy. The molecular weights calculated from sedimentation coefficients agree with the observed lengths. The sedimentation rates under alkaline conditions (where the composite single chains of many other viral DNA molecules completely separate) predict molecular weights that are one hald those of the duplex adenovirus DNA molecules. The majority of duplexes consist of uninterrupted poly-nucleotide chains. Finally, sedimentation under alkaline conditions reveals no detectable "supercoil" [long dash] that compact structure formed by the denaturation of an uninterrupted circular helix. The DNA''s isolated from adenovirions are linear duplex DNA molecules of 20-25 million daltons. Partial degradation of these molecules by exonuclease III followed by annealing rendered only 1 or 2% of them circular in the cases of Ad 2,4,7, and 18, and none circular in Ad 12 and 21. The significance of this low incidence of artificial circles is uncertain.