FIG. 2.

Effect of spermine and spermine analogues on poly(U)-directed Ac[³H]Phe-tRNA binding to ribosomes. The binding mixture (25 μl) was prepared in the absence (A) or presence (B) of the FWR fraction (10 μg of protein) and contained 100 mM Tris-HCl (pH 7.2), 100 mM NH₄⁺, 6 mM Mg²⁺ (acetate), 25.6 A₂₆₀ units of washed ribosomes per ml, 320 μg of poly(U) per ml, and, finally, spermine (○), N⁴,N⁹-dibenzylspermine (●), N¹-ethylspermine (□), N⁴,N⁹-bis(ethyl)spermine (▵), or N¹,N¹²-bis(ethyl)spermine (▴) at the indicated concentrations. The time course of the reaction was monitored up to 30 min at 25°C. The values of bound Ac[³H]Phe-tRNA were estimated from the maximum level of binding curves.