Artificial evolution and natural ribozymes.

In vitro selection techniques have been used to probe the sequence, structure, and function of natural ribozymes such as the viroid hammerheads and group I self-splicing introns. These artificial evolution experiments help to delimit the range of alternative structures and functions that are available to catalytic RNAs, and thus can provide insights into why particular sequences or mechanisms were fixed during the course of natural selection. Further, the wide variety of forms and functions that ribozymes have been found to assume in the laboratory provides inferential support for the hypothesis that much of modern metabolism may have been distantly derived from biochemistry centered on RNA rather than protein catalysts.