A Packing-Density Metric for Exploring the Interior of Folded RNA Molecules

The intricate architectures of RNA molecules often contain expansive close‐packed interfaces. The folding of the well‐defined P4‐P6 RNA domain was challenged by using a series of 2′‐modified nucleotides with a narrow range of molecular volumes. The resulting folding interferences (see picture) reflect the spatial environment of the 2′‐hydroxy groups and thereby define a packing‐density metric.