IN NATURE RNA AND PROTEINS ARE THE MATERIALS OF CHOICE FOR EVOLVING COMPLEX NANOMACHINES. ALTHOUGH MODERN LIVING ORGANISMS RELY HEAVILY ON PROTEINS FOR CATALYZING CHEMICAL REACTIONS ALL ENCODED PROTEINS ARE SYNTHESIZED BY THE RNA COMPONENT OF THE RIBOSOME ONE OF THE MOST ANCIENT CELLULAR MACHINERIES. THIS STRONGLY CORROBORATES THE RNA WORLD HYPOTHESIS THAT PROPOSES THAT EARLY LIFE WAS ESSENTIALLY BASED ON RNA AS THE KEY INFORMATIONAL BIOPOLYMER ABLE TO REPLICATE THE GENETIC INFORMATION AND ENABLING THE EVOLUTION OF PROTO-CELLS TOWARDS THE LAST UNIVERSAL COMMON ANCESTOR (LUCA) OF ALL LIVING ORGANISMS. AS SUCH THE RNA WORLD LIKELY PREDATED THE CURRENT BIOLOGICAL WORLD BASED ON DNA RNA AND PROTEINS. NEVERTHELESS MOLECULAR TRACES OF THE ANCESTRAL RNA POLYMERASE RIBOZYME HAVE REMAINED ELUSIVE WITHIN LIVING ORGANISMS. WHILE TREMENDOUS PROGRESS HAS BEEN ACHIEVED TOWARDS THE DEMONSTRATION OF RNA-BASED POLYMERIZATION IN VITRO SELECTED AND EVOLVED RNA POLYMERASE RIBOZYMES ARE STILL FAR FROM THE REMARKABLE EFFICIENCY OF MODERN PROTEINACEOUS RNA POLYMERASES. USING A COMBINATION OF RNA RATIONAL DESIGN SELECTION AND EVOLUTION TECHNIQUES AND BIOCHEMICAL CHARACTERIZATION APPROACHES THIS PROJECT AIMS AT ISOLATING COMPLEX RNA-BASED NANOMACHINES WITH ACTIVITY AND EFFICIENCY MATCHING THOSE OF MODERN PROTEINACEOUS RNA POLYMERASES. POSITED ON THE HYPOTHESIS THAT THE EVOLUTION OF PROTEIN TRANSLATION WAS TIGHTLY COUPLED TO THE EVOLUTION OF RNA REPLICATION MOLECULAR PALEONTOLOGY OF THE RIBOSOME HAS REVEALED THE EXISTENCE OF A REMARKABLE ARCHITECTURAL DOMAIN THAT WILL BE USED AS A STRUCTURAL SCAFFOLD FOR EVOLVING RNA POLYMERASE RIBOZYMES. THE EARLY CONDITIONS OF LIFE ON EARTH WERE VERY DIFFERENT FROM THE PRESENT ONES AND THE RNA WORLD AND PRE-LUCA ORGANISMS LIKELY EVOLVED IN AN ANOXIC ENVIRONMENT WITH IRON AND MANGANESE READILY SOLUBLE IN WATER. THEREFORE THE RETRO-SYNTHESIS OF RNA POLYMERASE RIBOZYMES WILL BE ACHIEVED BY IN VITRO EVOLUTION EXPERIMENTS PERFORMED IN PRESENCE OF IRON MANGANESE AND MAGNESIUM IN ANOXIC CONDITIONS PRESUPPOSED TO BE THOSE PREVAILING BEFORE THE EMERGENCE OF LUCA. THE RECOVERY OF EFFICIENT RNA-BASED NANOMACHINES SIMILAR TO THE ANCESTRAL RNA REPLICASE REPRESENTS ONE OF THE MOST FORMIDABLE CHALLENGES FOR UNAMBIGUOUSLY VALIDATING THE RNA WORLD HYPOTHESIS. MOREOVER THE CREATION OF RNA-BASED NANOMACHINES REPRESENTS A FORMIDABLE CHALLENGE FOR WHICH NEW STRATEGIES ARE NEEDED. COMPARISON OF THE OUTCOME OF IN VITRO EVOLUTION EXPERIMENTS PERFORMED IN ANOXIC VERSUS OXIC CONDITIONS WILL BE PARTICULARLY USEFUL FOR UNDERSTANDING BETTER HOW THE RNA WORLD MIGHT HAVE STRIVE BEFORE BEING SUPERSEDED BY AN RNA/DNA/PROTEIN WORLD. BESIDES DEMONSTRATING THE EXISTENCE OF THE MISSING LINK BETWEEN THE ANCESTRAL RNA WORLD AND THE LAST UNIVERSAL COMMON ANCESTOR THIS PROJECT WILL ALSO PROVIDE DESIGN PRINCIPLES OF BIOLOGICAL NANOMACHINES AND GENERATE REMARKABLE ORTHOLOGOUS MOLECULAR TOOLS FOR ENABLING THE FUTURE DEVELOPMENT OF NOVEL TECHNOLOGIES. THIS STUDY WILL CONTRIBUTE TO A BETTER UNDERSTANDING OF THE ORIGIN AND EVOLUTION OF FUNCTIONAL BIOMOLECULES TOWARDS GREATER COMPLEXITY. AS SUCH IT WILL HAVE TRANSFORMATIVE IMPACT IN THE FIELD OF ASTROBIOLOGY AS WELL AS IN THE NASCENT FIELD OF RNA SYNTHETIC BIOLOGY.