Related Experiment Video
Updated: May 29, 2026

Site-Specific Lysine Lactylation via Genetic Code Expansion in E. coli and Mammalian Cells
Published on: February 24, 2026
Expanding the genetic code of Escherichia coli with phosphoserine
Hee-Sung Park1, Michael J Hohn, Takuya Umehara
1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
Abstract:
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 (tRNA(Sep)), 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-tRNA(Sep) 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 (Sep(218), Sep(222)). This system has general utility in protein engineering, molecular biology, and disease research.
Related Concept Videos
Stringent Response in E. coli
From DNA to Protein
Coordination of Gene Expression Processes in Bacteria
Leaky Scanning

