Binding of Aminoacyl‐tRNA to Ribosomes Programmed with Bacteriophage MS2‐RNA

The secondary and tertiary structure of bacteriophage RNA is possibly concerned in the regulation of the synthesis of the three proteins encoded by this RNA. The accessibility of the beginning of the three cistrons for ribosomes should therefore be different. We decided to use the aminocyl‐tRNA binding assay to obtain proof of difference in accessibility. Binding studies with aminoacyl‐tRNA to ribosomes, programmed with bacteriophage MS2‐RNA, revelaed that, besides formylmethionyl‐tRNA, alanyl‐tRNA is also extremely well bound to the initiation complex. This result was taken to indicate that the beginning of the coatgene is the major ribosomal binding site with intact RNA. In experiments with other aminoacyl‐tRNAs it was shown that seryl‐ and lysyl‐tRNA rection. In most experiments no significant binding of arginyl‐tRNA could be recorded. Similar experiments were performed with framented MS2‐RNA of which it is known that the secondary and tertiary structure content is much lower. Binding results with fragmented MS2‐RNA revealed that the accessibility of the beginning of the different cistrons reached similar levels as indicated by the amount of binding of the following aminoacyl‐tRNAs: alanyl‐, seryl‐, lysyl‐ and arginyl‐tRNA. The synthesis of the formylmethionyl‐peptides : F‐Met‐Ala, F‐Met‐Ser, F‐Met‐Arg, F‐Met‐Ala‐Ser and F‐Met‐Ser‐Lys does occur in this binding reaction, although the efficiency of the dipeptide reaction is different for the various dipeptides involved.