[Construction of partial denaturation charts for DNA with random base distribution].

By measuring DNA temperature transition profiles the evidence was obtained that DNA of phages Tg9 and OB infecting Bacillus thuringiensis and Brevibacterium flavum respectively have a random base distribution. After alkaline treatment in the presence of 10 per cent formaldehyde at room temperature partially denatured molecules of phage Tg9 and OB DNA's with different degrees of denaturation were obtained. Using electron microscopy the maps of distribution of melted regions along these DNA's were obtained. The location of the main peaks on histograms did not vary with the increase of the degree denaturation and changes of pH values. The map of Tg9 DNA is characterized by four main peaks located at the positions 0.031, 0.075, 0.145 and 0.885 but the map of OB DBA is characterized by seven main peaks located at positions: 0.09, 0.20, 0.34 0.42,0.49, 0.80 and 0.88 from the left end (in relative units). The increase of denaturation up to a certain value did not change the half-width of the main peaks at the maps of these DNA's. It may be due to the presence in the DNA's some "heat stolle" sequences limiting early melting DNA regions.