Fig. 4. Ribosomal synthesis of N-terminal functionalized peptides with backbone-extended monomers.

a All backbone-extended amino acids (3–15) charged to tRNA^fMet(CAU) by Fx were incorporated into the N-terminus of a peptide by ribosome-mediated polymerization in the PURExpress^TM system. The peptides were purified via the Streptavidin tag (WSHPQFEK) and characterized by MALDI mass spectrometry. The observed mass of each peptide corresponds to the theoretical mass, which is b [M + H]⁺ = 1345; [M + Na]⁺ = 1367, c [M + H]⁺ = 1359; [M + Na]⁺ = 1381, d [M + H]⁺ = 1373; [M + Na]⁺ = 1395, e [M + H]⁺ = 1369; [M + Na]⁺ = 1391, f [M + Na]⁺ = 1351, g [M + H]⁺ = 1379; [M + Na]⁺ = 1401, h [M + H]⁺ = 1371; [M + Na]⁺ = 1393, i [M + H]⁺ = 1372; [M + Na]⁺ = 1394, j [M + H]⁺ = 1343; [M + Na]⁺ = 1365, k [M + Na]⁺ = 1365, l [M + H]⁺ = 1357; [M + Na]⁺ = 1379, m [M + H]⁺ = 1371; [M + Na]⁺ = 1393, n [M + H]⁺ = 1371; [M + Na]⁺ = 1393. The peaks denoted with an asterisk are a truncated peptide not bearing the target substrate at the N-terminus ([M + H]⁺ = 1246; [M + Na]⁺ = 1268). Data are representative of three independent experiments.