Ribosomal RNA supplementation highly reinforced cell-free translation activity of wheat germ

We have constructed an inexpensive, highly efficient eukaryotic cell-free translation system. Wheat germ rRNA (WG rRNA) was prepared by phenol/chloroform (P/C) extraction, a simple and quick method, from wheat germ, an inexpensive and commercially available by-product of flour production. Addition of a small amount of WG rRNA into a wheat germ cell-free translation system increased the protein productivity of the system 6- to 8-fold. Isolated 18S or 28S rRNA alone enhanced the protein production only 2-fold or 3.9-fold, respectively, at maximum. On the other hand, their equimolar mixture enhanced the production as much as the whole WG rRNA, indicating 18S and 28S rRNA synergistically functioned to enhance protein synthesis. Addition of WG rRNA slightly improved the stability of mRNA in the cell-free translation system, which explained only partly the enhancement of protein production. Addition of WGE or ribosome containing approximately the same amount of rRNA in the form of protein-rRNA complex as WG rRNA added to the system did not increase the protein production in the translation system. When ribosome in the cell-free translation system was replaced with WG rRNA, the system did not exhibit any detectable translation activity, indicating that the translation activity of WG rRNA is negligible in comparison with that of ribosome. These results indicated that WG rRNA affected some mechanisms regulating the translation rate in wheat germ cell-free system, resulting in increased protein production.