Enhancement of the Infectivity of Simian Virus 40 Deoxyribonucleic Acid With Diethylaminoethyl-Dextran2

The infectivity of viral RNA for mammalian cells in culture is greatly enhanced by diethylaminoethyl-dextran (DEAE-D). In this work a similar enhancing effect is shown for the infectious DNA of simian virus 40 (SV40). This phenomenon has enabled the development of a sensitive plaque method for the assay of infectious viral DNA; the reliability of the assay is in part accounted for by elimination of the need for exposure of the assay cells to hypertonic media. DEAE-D in Tris-buffered isosmolar media in concentrations of from 100 to 3000 μg/ml increases the infectivity of SV40 DNA up to 100,000 times. With DEAE-D's of molecular weight 26,000 to 2,000,000, DNA infectivity was directly related to molecular weight of DEAE-D. Paradoxically, DEAE-D produced a 20-fold reduction in infectivity of intact SV40. The degree of inhibition also depended on the molecular weight of DEAE-D, the number of SV40 plaques being inversely related to molecular weight. Since as much as 0.1% of viral infectivity can be recovered in the extracted DNA, it is now possible to prepare SV40 DNA with an infectivity titer high enough to initiate synchronous infection of all the cells in a culture.