Immunological recognition of polynucleotide structure.

Abstract

Since the discovery of polynucleotide Phosphorylase in 1955 and the availability of synthetic polynucleotides, a vast number of physical chemical studies have been pursued with such polymers, in particular by use of optical techniques. (For review see Michelson et al., 1967). It was early shown that complementary polynucleotides readily interacted to give DNA type double-stranded helical complexes. Since then, secondary structure in single strands, though less well defined, has been amply explored, as well as formation of triple-stranded complexes under certain conditions. All of these “natural” polymers and polymer complexes adopt a right-handed helical conformation in aqueous solution, and though left-handed structures have been proposed (these do indeed exist in polynucleotides containing L-ribose instead of D-ribose), no rigorous evidence of their existence in natural polynucleotides has been provided. Although the overall geometry is thus right-handed helical, a variety of geometrically distinct forms are known to exist, for example the A, B and C forms of DNA and the A form of double-helical RNA. In addition, chemical and physical studies have shown that synthetic polynucleotide complexes possess different absolute geometries in terms of double helix, and indeed two extreme DNAs, poly dAT from crab, and DNA from Micrococcus lysodeikticus (72% GC) show quite different structures.