The Effects of Polyamines on the Melting of Polyriboadenylic Acid Plus Polyribouridylic Acid Complexes in a Solution

Ultraviolet absorptions of aqueous systems of polyriboadenylic acid (poly A) plus polyribouridylic acid (poly U) have been examined with various Na+ and Mg2+ concentrations and at various temperatures. The transition temperatures (Tm) among the two-stranded conformation, poly(A+U), the three-stranded conformation, poly(A+2U), and the two single-stranded conformations, poly A and poly U, were determined. The effects upon the Tm of adding NH3+-(CH2)nNH3+-type diamines (n=2, 3, 4, 5, 6, and 8), spermine, and actinomycin D to the solutions were observed. It was found that these amines stabilize three-stranded poly(A+2U) more than they stabilize the two-stranded (poly(A+U)) and the single-stranded (poly A and poly U) conformations. Among the diamines examined, those with n=2 and 3 values show a greater effect than those with n=4, 5, 6, and 8 values.