Expanding the Genetic Code of Escherichia coli with Phosphoserine

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Science  26 Aug 2011:
Vol. 333, Issue 6046, pp. 1151-1154
DOI: 10.1126/science.1207203

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O-Phosphoserine (Sep), the most abundant phosphoamino acid in the eukaryotic phosphoproteome, is not encoded in the genetic code, but synthesized posttranslationally. Here, we present an engineered system for specific cotranslational Sep incorporation (directed by UAG) into any desired position in a protein by an Escherichia coli strain that harbors a Sep-accepting transfer RNA (tRNASep), its cognate Sep–tRNA synthetase (SepRS), and an engineered EF-Tu (EF-Sep). Expanding the genetic code rested on reengineering EF-Tu to relax its quality-control function and permit Sep-tRNASep binding. To test our system, we synthesized the activated form of human mitogen-activated ERK activating kinase 1 (MEK1) with either one or two Sep residues cotranslationally inserted in their canonical positions (Sep218, Sep222). This system has general utility in protein engineering, molecular biology, and disease research.

  • Present address: Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.

  • Present address: Department of Chemistry, Angelo State University, San Angelo, TX 76909, USA.

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