THE ACCOMMODATION OF NONCOMPLEMENTARY BASES IN HELICAL POLYRIBONUCLEOTIDES AND DEOXYRIBONUCLEIC ACIDS

Abstract

A quantitative study has been made of the helical complex formation between poly-riboadenylic acid or polyuridylic acid and copolymers containing residues common to both members of this complementary pair. The interaction occurs in such a manner that the two-stranded helical complexes formed always contain equal moles of homopolymer residues and complementary residues in the copolymers. This indicates that the noncomplementary residues in the copolymers loop out of the helix. Model building shows that this can be done without altering the essential structural features of the helix, and that loops of one or more residues are feasible. While these loops do weaken the helix, it is apparent that the number of mismatchings which can be tolerated in a DNA-like helix is quite large. The relevance of these findings to DNA is considered, and hypothetical schemes for the accommodation of point mutations by forming such loops are presented.