[Conformational possibilities of the regular single-stranded polyribonucleotides].

It was shown that in case of C(3')-endo pucker of ribose two left and two right types of helices are possible from the energetical point of view. However, such helices with C(2')-endo conformation of ribose are extremely unfavourable due to the steric hindrance caused by 2'-OH group. In this case the low energy structures have bases outside and phosphate groups inside the helix. The right and the left poly(A) helices have similar energy values, the barrier of transition between them being rather small. Biregular structures, i.e. the helices on which dinucleotide serves as the repeating unit, were also considered. These forms proved to be energetically optimal in the case of poly(A-C).