Square-shaped RNA particles from different RNA folds.

The structural information encoding specific conformations of natural RNAs can be implemented within artificial RNA sequences to control both three-dimensional (3D) shape and self-assembling interfaces for nanotechnology and synthetic biology applications. We have identified three natural RNA motifs known to direct helical topology into approximately 90 degrees bends: a five-way tRNA junction, a three-way junction, and a two-helix bend. These three motifs, embedded within rationally designed RNAs (tectoRNA), were chosen for generating square-shaped tetrameric RNA nanoparticles. The ability of each motif to direct the formation of supramolecular assemblies was compared by both native gel assays and atomic force microscopy. While there are multiple structural solutions for building square-shaped RNA particles, differences in the thermodynamics and molecular dynamics of the 90 degrees motif can lead to different biophysical behaviors for the resulting supramolecular complexes. We demonstrate via structural assembly programming how the different 90 degrees motifs can preferentially direct the formation of either 2D or 3D assemblies.