Project Summary/Abstract This proposal explores three major aspects of synthetic biology- all under the related theme of the evolution of life: a look forward into evolution by creating organisms with an expanded genetic code, and a look back into evolution by exploring the evolution of mitochondria in a well- defined “synthetic” endosymbiont system, and by exploring one possible mechanism for the transition from the RNA to DNA world through the generation and characterization of bacteria with chimeric DNA-RNA genomes. Specifically, we will genetically encode D-amino acids in bacteria and create and apply a genetically encoded tool to study protein folding/unfolding on a sub-microsecond timescale; we will begin to minimize our bacterial endosymbiont genome by deleting metabolic and cell wall biosynthetic genes, as well as exploring those factors that contribute to the stability of this chimeric system; and create a biorthogonal replication system and use it to explore those factors that allow the incorporation of large numbers of ribonucleotides into bacterial DNA.