RNA Strand, Trefoil Knot (IMAGE) International School of Advanced Studies (SISSA) Caption Pictured is a computer-generated RNA structure tied in a trefoil knot. C. Micheletti et al. screened the several thousand RNA chains in the Protein Data Bank for the presence of knots. Only three knotted instances were found, though their comparison with higher resolution homologs indicates that their knotted state is likely artifactual. The practical absence of physical knots in known RNA chains contrasts with the documented incidence of knots in other biomolecules (proteins and viral DNA) and suggests that thermodynamic or kinetic mechanisms may be at play for minimizing the entanglement of naturally-occurring structured RNAs. Credit SISSA (Micheletti) Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.