This suggests that the conformational fluctuations of the M5 active site, which we quantified with enhanced sampling simulations, may have a broader relevance for RNases. We found that these distinct conformations of the active sites where correlated with larger scale conformational fluctuations of the interface, and notably with fraying motions at the RNA ends. Here, we have to pause and note that in vivo, the RNA 3 ′ end is much longer than in our simulations (42 nucleotides), but this part of the RNA is unstructured and not resolved in the cryoEM structure of the complex. This suggests that the RNA 3 ′ end is indeed very flexible and prone to adopt varied conformations. While the exact populations of different conformational states may differ in the full-length system, we can thus reasonably assume that large conformational fluctuations may occur at the RNA ends and lead to distinct populations of active site structure.