Scientists have figured out what makes DNA, not RNA, the best molecule to store genetic information. The findings are in a study just published in the journal Nature Structural and Molecular Biology.
Deoxyribonucleic acid, or DNA, stores instructions for making proteins that support life and reproduction. Another nucleic acid, RNA, plays roles in gene translation and expression but does not store genetic information on its own. While DNA consists of two strands in a double-helix shape, RNA is generally single-stranded. Scientists have assumed that the double-helix shape is critical for DNA’s function but whether or not RNA could maintain the same form was unknown.
Researchers from the Duke University School of Medicine wanted to investigate what would happen if RNA took the shape of a double-helix. It’s well-known that DNA lines up according to Watson-Crick base pair rules but the molecule also takes on a different form for brief periods of time. While in what’s called the Hoogsteen configuration, geometry is slightly changed and base pairs are rotated. The research team wondered if RNA would be able to take on this alternative configuration.
By using a technique called NMR relaxation dispersion, the team was able to track and observe molecular changes in the RNA strands. They found no evidence of Hoogsteen base pair rules in the RNA. To further confirm the results, the researchers used a chemical to force RNA into a Hoogsteen configuration. The RNA helix fell apart, showing an inability to change shape from the standard Watson-Crick form.
The researchers speculate that RNA lacks the flexibility to change shape because its structure is more compressed than DNA’s structure. RNA can’t easily move its bases around without bumping into other molecules, potentially leading to breakage. Since switching to a Hoogsteen configuration helps DNA repair damage, RNA would be a poor molecule for storing all of our genetic information. These results provide new insights into how DNA and RNA function while outlining the importance of DNA’s flexible shape.
Huiqing Zhou et al. m1A and m1G disrupt A-RNA structure through the intrinsic instability of Hoogsteen base pairs. Nature Structural and Molecular Biology (2016).