Cryo-EM Reveals Protein-Free RNA Structures in Bacterial Cells

Cryogenic electron microscopy showed for the first time that large RNA complexes can assemble without the help of proteins, expanding our understanding of RNA folding and function. 

Ribonucleic acid (RNA) molecules may be best known for their job ferrying the genetic information encoded in DNA to a cell’s protein factories, but these molecules aren’t just a middleman for protein production. In fact, some RNA molecules don’t code for proteins at all and serve various other important functions in cells, such as regulating gene expression and catalyzing chemical reactions. However, the functions of many non-coding RNAs remain mysterious.

Now, searching for hints about the roles of a trio of non-coding RNA molecules produced en masse in bacterial cells, researchers from Stanford University, the Department of Energy’s SLAC National Accelerator Laboratory, and the National Institutes of Health stumbled upon unexpectedly extravagant, multistrand complexes made entirely of RNA, which the team reported today in the journal Nature.

We discovered that these RNAs fold into beautiful symmetric complexes without any proteins or other molecules to support them. This is something we haven't seen before in nature.”

Rachael Kretsch, Stanford graduate student and lead author 

The discovery expands our current understanding of how RNA assembles into large, complex structures, and it could even inspire the design of similar structures for biomedical or biotechnological purposes, the researchers said.