4. The genetic codes were deciphered by simply using the in vitro protein synthesis system Artificially synthesized poly(U), synthesized using polynucleotide phosphorylase, was added to 20 reaction tubes each containing the cell-free E coli extract, GTP, atp a mixture of 20 amino acids and one 14C labeled amino acid Radioactive polypeptide was only detected in the tube containing [4C]-Phe(with high concentration of Mg2+t When poly(a)and poly(c) were added, radioactive polypeptides were only detected in the tubes containing 14C-labeled L-Lys and L-Pro respectively4. The genetic codes were deciphered by simply using the in vitro protein synthesis system • Artificially synthesized poly(U), synthesized using polynucleotide phosphorylase, was added to 20 reaction tubes each containing the cell-free E.coli extract, GTP, ATP, a mixture of 20 amino acids, and one 14C labeled amino acid. • Radioactive polypeptide was only detected in the tube containing [14C]-Phe (with high concentration of Mg2+ ). • When poly (A) and poly (C) were added, radioactive polypeptides were only detected in the tubes containing 14C-labeled L-Lys and L-Pro respectively