Translation of poly(A) in eukaryotic cell-free systems

Translation of poly(A) in eukaryotic cell-free systems was investigated in comparison with that of poly(U), using the E. coli cell-free system as a control, and the following results were obtained. 1. Poly(A) was not translated in the eukaryotic cell-free systems prepared from yeast, wheat embryos, and rat liver, whereas poly(U) was well translated in these systems. On the other hand, fairly good translation of poly(A) as well as poly(U) was observed in the E. coli cell-free system. 2. The inefficient translation of poly(A) observed in the eukaryotic systems was not due to the lack of lysyl-tRNA synthetase, because of addition of [14C]lysyl-tRNA did not improve the synthesis of polylysine dependent on poly(A). 3. Eukaryotic ribosomes such as those prepared from Artemia salina did not bind [3H]poly(A) but bound [3H]poly(U) in the absence of tRNA, whereas they bound both polynucleotides if tRNA was present. Furthermore, the binding of [3H]poly(A) to A. salina ribosomes observed in the presence of tRNA was strongly dependent on the incubation temperature, indicating that the interaction between ribosomes and poly(A) was hampered by the base stacking known to be present in poly(A). Thus, tRNA seemed to be required for the formation of the stable ribosome-poly(A) complex. 4. Binding of [14C]lysyl-tRNA to ribosomes, either of A. salina or of E. coli, was observed as well as that of [14C]phenylalanyl-tRNA. In contrast, chain elongation of polylysine was extremely slow in the eukaryotic system as compared with the E. coli system, although chain elongation of polyphenylalanine proceeded equally well in both systems, and this resulted in poor synthesis of polylysine in the eukaryotic systems.