Ribozymes with aldolase-activity by in vitro-evolution

All higher life on Earth appears to rely on DNA genomes and protein enzymes. It is generally accepted, however, that this DNA-protein-world was preceded by a time when all of the functions of life were carried out by RNA- molecules, referred as the "RNA-world". This scenario has gained credence with the recent discoveries of ribozymes capable of catalyzing various steps in RNA biosynthesis. These ribozymes were obtained by "in vitro evolution", a model of evolution in the RNA world, which applies Darwinian principles to molecular systems improving the fitness of RNA enzymes by repetitive rounds of mutation and selective amplification. Yet there is no ribozyme that catalyzes the synthesis of crucial RNA-building blocks, in particular ribose. One potential biosynthetic pathway to ribose is the aldol reaction from glycoaldehyde and glyceraldehyde. We aim to utilize in vitro evolution to obtain a ribozyme with aldolase activity, which is required to explain the present-day dominance of ribose (and deoxyribose) as the only sugar building block of genetic material. Furthermore, the aldol reaction is broadly utilized for C-C-bond formation in organic chemistry, and a method for obtaining selective catalysts for this reaction is highly desired. We aim to develop a family of aldolase ribozymes employing both conventional and "continuous" in vitro evolution methods, that later approach enabling a dramatically increased speed of evolution. The selection scheme will involve covalent attachment of a promoter-containing oligonucleotide as a consequence of the aldol reaction. Successful catalysts will have this oligonucleotide joined to their 5` end through a ribose linker, thus becoming eligible for selective amplification. Similar methods might be applied to develop selective catalysts for a number of organic reactions that involve a joining reaction between two attached substrates.