The principal component analysis was conducted for the coordinates of the CA atoms of the protein and the P and C4' atoms of the RNA. The simulation frames plotted against the first two principal components (PC) are shown in Figure on the left panel. On the right panel are shown the loadings of the atoms that were used to calculate the first PC. The PC loadings and weights show that the different force fields are generally not sampling a similar conformational space and the largest movements are not contributed by a certain part of the complex in all cases. The residue numbers that had the highest weights for the first PC are shown in Supporting Information Table .