One-Step Release of DNA Rings From Polyoma Virions

Abstract

A tightly packed regularly coiled DNA ring is assumed to be present inside the polyoma virion. Applying the “one-step” technique of nucleic acid extraction from virions while being adsorbed to a protein monolayer, we studied the configurational changes of the DNA.Intact polyoma virions were mixed with DFP-trypsin (100μg/ml) and spread onto a subphase of a mixture of urea and sodium perchlorate (6M and 2M, or 3M and 1M respectively), at pH 8.2 and room temperature. After spreading the film, aliquots were transferred to grids at different periods of time, and the DNA stained by acetonic uranyl acetate.The length distribution of the DNA molecules measured from electron micrographs is shown in Fig. 1. The number of twists present at different times after spreading were also counted. At 12 minutes, with 3M urea and 1M sodium perchlorate in the subphase, the DNA was found to be 85% supertwisted (Fig. 2); 12% was opened to rings, and 3% existed as linear filaments.