Boundaries for an RNA world.

Before large, specific peptides could be made, in an RNA world our ancestors may have used an RNA-like molecule for both catalysis and information storage. Taken together, RNA activities suggest RNA could have performed most of the essential informational functions of an ancient organism (i.e. those functions most similar to RNA's role today). In contrast, though compellingly reasoned optimism about RNA-catalyzed small-molecule metabolism is plentiful, fundamental problems remain to be solved.