Effect of ionic conditions on DNA melting curve parameters

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Abstract
Systematic experimental data for the dependence of melting range width ΔT for phage T2 and calf thymus DNA's on sodium ion concentration was obtained. A mathematical description of helix‐coil transition was given for the case of DNA with a block sequence of nucleotides (such as calf thymus DNA). This description predicts an almost linear dependence of ΔT for DNA from higher organisms on the value TGC‐TAT. On the other hand, ΔT is proportional to (TGC‐TAT)1.6 for DNA's with quasi‐random sequences (such as phage T2 DNA). Experimental data fully confirmed the theoretical predictions.The dependence of TGC‐TAT on sodium ion concentration was determined. The most striking feature of this dependence is the sharp rise in TGC‐TAT in the region of low sodium ion concentration (< 3 × 10−3) up to 100°C. The dependence of TGC and of TAT on ionic strength was calculated separately. In the region of low ionic strength, these quantities show markedly different behavior.