EMPIRICAL EXPLORATIONS OF SEQUENCE SPACE - HOST-GUEST CHEMISTRY IN THE RNA WORLD

Using data from a number of recent in vitro selection experiments, gen eral conclusions have been drawn about the shapes of landscapes that m ap nucleic acid sequences to functions (in particular, the ability to bind a ligand). It appears that local optima on these landscapes are d ispersed; that is, that there are a variety of sequences that can bind to a given ligand. In addition, though, there are usually one or two apparently global optima. A comparison of aptamer shapes suggests that nucleic acids can easily form simple pockets by using short helical s egments. These results have implications for the origin and evolution of metabolism: short nucleic acids may be much better suited to ligand -binding than short peptides or other biopolymers.