[Nature of the easily melted portions of DNA with a quasi-random base sequence]

The influence of denaturation conditions upon the character of partial denaturation of DNA with random base distribution were thoroughly studied. Maps of partial DNA denaturation were obtained at T less than TAT for phage phiB DNA at pH 10.7 and 5.5; Tg9 DNA at pH 8.8; at T less than TAT for phiB DNA at pH 10.9 and Tg9 DNA at pH 8.8. The map quality was better when obtained at higher pH values; the peaks became sharper and higher against the background. We failed to obtain maps of partial denaturation at pH 5.5, T less than TAT. The improvement of the map quality and existence of the partial denaturation maps at T less than TAT at pH 10.9 were explained by the increase of primary melting probability of AT-rich DNA regions. At high pH the denaturation map quality was temperature independent. This was explained by a very weak temperature dependence of primary melting probability for all maps of equal quality. The map quality became worse, when the quantity of loops was increased.