This invention provides compositions and methods for generating components of protein biosynthetic machinery including orthogonal tRNAs, orthogonal aminoacyl-tRNA synthetases, and orthogonal pairs of tRNAs/synthetases. Methods for identifying orthogonal pairs are also provided. These components can be used to incorporate unnatural amino acids into proteins in vivo.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
 The invention was made with United States Government support under Grant No. N0001498F0402 from the Office of Naval Research, Contract No. NIH GM62159 from the National Institutes of Health, and Contract Nos. DE-FG03-00ER45812, DE-AC03-76SF00098 from the Department of Energy. The United States Government has certain rights in the invention.