2 DOUBLE HELICAL FORMS OF POLYRIBOADENYLIC ACID AND PH-DEPENDENT TRANSITION BETWEEN THEM

Well-oriented X-ray diffraction patterns from acid-drawn fibres of polyriboadenylic acid, show that it can exist in either of two phases, or a mixture of both, depending on pH, the transition being possible within the fibre. The X-ray diagrams of both phases agree with double-helical structures, which are closely related. The chains in the double helix formed at lower pH's (5 to 6) are more extended than those in the helix formed at higher pH's (6 to 7). © 1969.