Complex formation between spin-labeled polyuridylic acid and pyrimidine nucleosides.

Complex formation between poly (U) and pyrimidine nucleosides, uridine and cytidine, was observed using spin labeling technique. The binding of these nucleosides with poly (U) takes place within a narrow range of their concentration and is characterized by a relatively strong cooperativity. It is shown, that both hydrogen bonding and stacking interaction contribute to the complex stability. Some thermodynamic parameters of the process were obtained from the binding isotherms. At 21 degrees C the equilibrium constants for nucleation were found to be 0.23 M-1 and 0.42 M-1, and those for chain growth 2.63 M-1 and 2.19 M-1 for uridine and cytidine respectively. Complex formation of poly (U) with adenosine was also studied by spin labeling method.