Proceedings of the National Academy of Sciences of the United States of America
Spermidine-condensed phi X174 replicative form (RF) II DNA was digested with micrococcal nuclease to yield seven identifiable DNA bands forming an arithmetic fragment-length series. The DNA monomer unit length was found to be 780 +/- 80 base pairs. This result is most consistent with a proposed model for micrococcal nuclease cleavage of a DNA torus organized by the unidirectional, circumferential wrapping of B-geometry DNA. By a topological consideration, the blunt-end-rod-fusion model for torus formation [Eickbush, T. H. & Moudrianakis, E. N. (1978) Cell 13, 295-306] is shown to be inconsistent with our empirical solution results. We propose a continuous, circumferential DNA wrapping model in which a significant fraction of the collapsed circular phi X174 RFII DNA molecules form regular toruses comprised of seven complete, unidirectional double-helical wraps.
Marx, Kenneth A. and Reynolds, Thomas C., "Spermidine-Condensed Phi X174 DNA Cleavage by Micrococcal Nuclease: Torus Cleavage Model and Evidence for Unidirectional Circumferential DNA Wrapping." (1982). Open Dartmouth: Faculty Open Access Articles. 1244.