The unfolding of our understanding of RNA structure: a personal reflection

In this article, I review how our research on RNA began, how it led us to demonstrate the single-stranded nature of RNA, and the ways in which it differs from double-stranded DNA. It was based on the development of a method for the isolation of undegraded rRNA and the observation that in rRNA preparations due to their viscosity behavior resemble a flexible, contractile coil. In support of this assumption, birefringence of flow measurements showed that rRNA solutions gave moderate positive values, which disappeared upon addition of salt. This is in contrast with DNA solutions where considerable negative birefringence persists even in the presence of salt. Further studies on RNA showed a close correlation of the ionic strength dependencies of optical rotation, optical density and hydrodynamic properties. These early results indicated that rRNA and tRNA possess a significant secondary structure. I then review the basis of the hairpin model for the secondary structure of RNA and finally, summarize current understanding of the tertiary structure of RNA.