1964: The first model for the shape of a transfer RNA molecule. An account of an unpublished small-angle X-ray scattering study

The shape of non-fractionated Escherichia coli transfer RNA molecules in solution was investigated using small-angle X-ray scattering during the years 1960-1962 at the Centre de Recherche sur les Macromolécules in Strasbourg. The innermost region of the scattering curve yielded the average molecular weight (Mr) and the radius of gyration (Rg) of the particles, whereas the experimental data at large angles could be approximated at best by the scattering curve of a kinked rod-shaped molecule. The simplest model that was compatible with Mr, Rg, and the mass per unit length of the rod was a boomerang-shaped particle made of two double helical stems connected by a sharp kink. This model that eventually proved similar to the high-resolution L-shaped structure, was presented in my Ph.D. dissertation (J. Witz, Etude de la structure de quelques polynucléotides en solution par diffusion centrale des rayons X, Ph.D. dissertation, University of Strasbourg, France, 1964) but has never been published in detail. It is the purpose of this note to recall this story.