Computer analysis of conformational possibilities of double‐helical DNA

X-ray analysis has revealed the existence of several forms of the double-helical nucleic acid: A, B, C [1 ], T [2] and D [3]. It is therefore important to obtain a complete description of all possible conformations of the complementary helix. Tumanyan and Essipova [4] have suggested an algorithm which allows one to obtain the base pairs position, if four of the six independent dihedral angles, controlling DNA geometry, are known. Here we present an alternative approach which permits, starting from positions of the bases (Arnott's parameters [1]), to f'md all the poss~le structures of the sugar-phosphate backbone and to calculate energy values of the helices. With this method we are able to suggest a general classification of the forms of the regular double-helical nucleic acid and to obtain interrelationships between the variables, characterizing the spatial structure of the double helix.

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