As you may already know, the
Protein Data Bank (PDB) holds
experimentally determined 3D structures of macromolecules, including DNA, RNA, and their complexes with proteins and small molecules. Other than that, there exist computataional tools to predict 3D RNA structures from given base sequence, see
RNA Puzzles. However, it is up to the users to decide whether a specific prediction is meaningful.
It is worth noting that, by and large, 3DNA does
not predict 3D structures from 1D sequences. It does the opposite: by starting from a 3D model, 3DNA calculates a set of geometrical parameters to characterize the structure.
Xiang-Jun