Structural variations of DNA + Mn 2+ complexes during helix‐coil transition

The helix‐coil transition in Phage T2 DNA in the presence of 6,4 · 10 −3 mol/l Mn 2+ is studied using light scattering and UV spectroscopy. The transition range is about 0,5°C. Near the temperature of the end of melting T f the molecular weight M w and the radius of gyration R z of the complex are observed to decrease to about one half. At a temperature 0,1–0,25°C higher than T f , M w and R z pass through a minimum, which implies that aggregation is preceded by unwinding of DNA strands. Thus, rise in temperature rather than Mn 2+ ‐induced aggregation causes DNA + Mn 2+ melting.