Abstract We describe the modeling method for RNA tertiary structures employed by team AIchemy_RNA2 in the 15 th Critical Assessment of Protein Structure Prediction (CASP15). The method consists of the following steps. Firstly, secondary structure information was derived from various manually-verified sources. With this information, the full length RNA was fragmented into structural motifs. The structures of each motif were predicted and then assembled into the full structure. To reduce the searching conformational space, a RNA structure was organized into an optimal base folding tree. And to further improve the sampling efficiency, the energy surface was smoothed at high temperatures during the Monte Carlo sampling to make it easier to move across the energy barrier. The statistical potential energy function BRiQ was employed during Monte Carlo energy optimization.

RNA tertiary structure modeling with BRiQ potential in CASP15