Helix-with-loops structure of polynucleotide. II. Poly(I+CU).

Abstract

AbstractCopolymers of ribocytidylic acid (C) and ribouridylic acid (U) with C contents of 66.5 and 43 mole‐% have been prepared. Ultraviolet, absorption measurements were made of aqueous solutions of the mixtures of these copolymers (poly CU) and polyriboinosinic acid (poly I). In every set of examinations, a maximum hypochromicity (at 230, 248, or 260 mμ) was observed when the solution contained equal moles of C residue in the copolymer and I residue in the homopolymer. This fact was interpreted as indicating that a helix‐with‐loops structure, similar to that proposed by Fresco and Alberts7, is formed. It was shown that this structure is formed more rapidly and melts more sharply than that observed by Fresco and Alberts. An infrared examination was also made of this “helix‐with‐loops” structure. It was found that a few absorption bands are assignable to the helix part and a few other bands to the loop part of the structure.