View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Leading Edge Essay Discovering the RNA Double Helix and Hybridization Alexander Varshavsky1,* 1Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA *Contact:
[email protected] DOI 10.1016/j.cell.2006.12.008 The discovery, 50 years ago, that RNA could form a double helix made possible a number of advances, including an understanding that led, decades later, to the discovery of micro- RNAs and RNA interference. Remarkably, the first nucleic acid hybridization reaction was also described in the same report. It is difficult to imagine today how little two papers in which they analyzed naturally occurring RNA. These syn- was known about the molecular basis X-ray diffraction photographs of thetic RNA chains were apparently of living cells 50 years ago. The DNA RNA fibers (Rich and Watson, 1954a, linear, suggesting that the natural double helix, described in the 1953 1954b). The diffraction patterns they RNA molecules would not contain Watson and Crick Nature paper (Wat- saw were too diffuse for a definitive significant branching. son and Crick, 1953), was a uniquely statement about the underlying RNA important insight into a molecular structure. It was puzzling that the The Key Discovery structure that could both contain same diffraction pattern was pro- In the spring of 1956, Rich and Dav- genetic information and replicate it. duced by RNA molecules that had ies found that, on mixing sodium However, the role of the other nucleic vastly different base ratios, unlike the salts of polyadenylic acid (poly A) and acid, RNA, was clothed in uncertainty.