[Peculiarities of primary and secondary structure of phage FI-1 DNA]

The composition of nitrous bases of phage FI-1 DNA was studied. As is evidenced from the values of buoyant density in CsCl (p=1,7093 g/cm(3)), melting temperature (T degrees m=86,05 degrees), spectral parameters and direct chromatographic determination, the DNA analysed contains 41,5 mole% pairs of guanine-cystosine. 5-hydroxymethylcytosine and other anomalous bases were not found. Chemical identification and jaxtposition of data of buoyant density in CsCl and Cs2SO4 (p=1,4466 g/cm(3)) and T degrees m. showed the presence of the extra-sugar component in DNA, most likely in the form of hentibiose. Spectral character of thermal denaturation of DNA in different solvents is indicative of the double helixity of its structure. DNA is characterized by enthalpies of conformational transitions "helix coil" (deltaH=12,3 kcal/g) and (deltaH=10 kcal/g) for the solvents, 1 x SSC, and 0,1 x SSC, correspondingly. The presence of extra-sugar in DNA with standard set of nitrous bases is discussed.