Published in: Science, vol. 289, no. 5478, pp. 448-452 (July 21, 2000):

Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge, MA 02142

* To whom correspondence should be addressed.
E-mail: dbartel@wi.mit.edu

We describe a single RNA sequence that can assume either of two ribozyme folds and catalyzes the two respective reactions. The two ribozyme folds share no evolutionary history and are completely different, with no base pairs (and probably no hydrogen bonds) in common. Minor variants of this sequence are highly active for one or the other reaction, and can be accessed from prototype ribozymes through a series of neutral mutations. Thus, in the course of evolution, new RNA folds could arise from preexisting folds, without the need to carry inactive intermediate sequences. This raises the possibility that biological RNAs having no structural or functional similarity might share a common ancestry. Furthermore, functional and structural divergence might, in some cases, precede rather than follow gene duplication.

1. "Oncogenes as Molecular Targets within Active Chromatin".

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