Role of Dna Concentration

M elting temperatures {T m ) o f several D N A ’s do not vary w ith the change o f D N A concentra­ tion. However, at any temperature above Tm , the fractional hyperchromism was always greater at the lower concentration. Th is result was also evident in the presence o f formaldehyde. Revers ib ility on renaturation decreased w ith the progress o f thermal denaturation along the m elting profile. The effect was much enhanced at low D N A concentration and for a D N A of low G — C content. The occurrence o f some permanent changes on the dissociated molecules has been suspected to be the only cause for the observed effects.