The yeast split-hybrid system

Progress toward an expanded eukaryotic genetic code

Expanding the eukaryotic genetic code to include unnatural amino acids with novel properties would provide powerful tools for manipulating protein function in eukaryotic cells. Toward this goal, a general approach with potential for isolating aminoacyl-tRNA synthetases that incorporate unnatural amino acids with high fidelity into proteins in Saccharomyces cerevisiae is described. The method is based on activation of GAL4-responsive HIS3, URA3, or lacZ reporter genes by suppression of amber codons in GAL4. The optimization of GAL4 reporters is described, and the positive and negative selection of active Escherichia coli tyrosyl-tRNA synthetase (EcTyrRS)/tRNA(CUA) is demonstrated. Importantly, both selections can be performed on a single cell and with a range of stringencies. This method will facilitate the isolation of a range of aminoacyl-tRNA synthetase (aaRS)/tRNA(CUA) activities from large libraries of mutant synthetases.

The use of selective adsorbents in capillary electrophoresis-mass spectrometry for analyte preconcentration and microreactions: a powerful three-dimensional tool for multiple chemical and biological applications

Much attention has recently been directed to the development and application of online sample preconcentration and microreactions in capillary electrophoresis using selective adsorbents based on chemical or biological specificity. The basic principle involves two interacting chemical or biological systems with high selectivity and affinity for each other. These molecular interactions in nature usually involve noncovalent and reversible chemical processes. Properly bound to a solid support, an "affinity ligand" can selectively adsorb a "target analyte" found in a simple or complex mixture at a wide range of concentrations. As a result, the isolated analyte is enriched and highly purified. When this affinity technique, allowing noncovalent chemical interactions and biochemical reactions to occur, is coupled on-line to high-resolution capillary electrophoresis and mass spectrometry, a powerful tool of chemical and biological information is created. This paper describes the concept of biological recognition and affinity interaction on-line with high-resolution separation, the fabrication of an "analyte concentrator-microreactor", optimization conditions of adsorption and desorption, the coupling to mass spectrometry, and various applications of clinical and pharmaceutical interest.