to be of practical use, catalytic antibodies have provided important new insights in our understanding of biocatalysis, structural plasticity of proteins, evolution of biochemical function, and the immune system itself. Schultz then applied molecular diversity—the strategy of creating a large community of different molecules, plus a method for fishing out and identifying the ones that do what you want—to a range of problems in chemistry, biology and materials science. Along with Richard Lerner, he was one of the critical players in the development of phage-display libraries, and surface-library chips. For high-throughput bioassays which require freely soluble test-compounds, he uses microrobotic fluid-manipulation systems, adapted for 1,536-microwell cell-culture plates, to separately treat very small cell colonies with large numbers (hundreds of thousands) of different compounds. Using these various high-throughput and combinatorial experimental approaches, Schultz has identified materials with novel optical, electronic, and catalytic properties; also, proteins and small molecules which control important biological processes such as aging, cancer, autoimmunity, and stem-cell differentiation and de-specialization back to pluripotency. Unnatural amino acids Schultz has pioneered a method for adding new building blocks, beyond the common twenty amino acids, to the genetic codes of prokaryotic and eukaryotic organisms. This is accomplished by screening libraries of mutant amino acyl tRNA synthetases for mutants which charge nonsense-codon tRNAs with the desired unnatural amino acid. The organism which expresses such a synthetase can then be genetically programmed to incorporate the unnatural amino acid into a desired protein in the usual way, with the nonsense codon now coding for the unnatural amino acid. Normally, the unnatural amino acid itself must be synthesized in the lab and supplied to the organism by adding it to the organism's growth medium. The unnatural amino acid must also be able to pass through the organism's cell membrane into the interior of the organism. More than seventy unnatural amino acids have been genetically encoded in bacteria, yeast, and mammalian cells, including photoreactive, chemically reactive, fluorescent, spin-active, sulfated, pre-phosphorylated, and metal-binding amino acids. This technology allows chemists to probe, and change, the properties of proteins, in vitro or in vivo, by directing novel, lab-synthesized chemical moieties specifically into any chosen site of any protein of interest. A bacterial organism has been generated which biosynthesizes a novel, previously unnatural amino acid (p-aminophenylalanine) from basic carbon sources and includes this amino acid in its genetic code. This is the first example of the creation of an autonomous