Overview of a system for cell-free production of natural products via nonribosomal peptide biosynthesis. From left to right, exogenous DNA is used as the input information for the production of biosynthetic enzymes. In the center, nonribosomal peptide synthetase proteins function in concert to select substrates and catalyze the formation of peptide bonds, ultimately resulting in the production of a 2,5-diketopiperazine. Right panel, detection of a d-Phe-l-Pro diketopiperazine natural product by LC–MS as the result of in situ production of biosynthesis proteins.