There are several algorithms which attempt to predict the secondary structure of RNA molecules such as Vienna, but, it seems, precious little experimental data. Some structures, such as tRNA, have been solved via X-Ray crystallography and NMR, but there seems to be no general repository of RNA structures, akin to the RCSB PDB repository for proteins. I have very little knowledge of NMR/X-ray crystallography, but it seems that determination of RNA structures would be simpler than protein structures due to their smaller sizes (though perhaps this is offset by their greater flexibility?). I'd wager that experimentally derived structure data would be vastly useful for RNA-targeted drug design, and evaluation of secondary-structure prediction algorithms.

What I'd like to hear opinions on is: a) Are there ongoing efforts to determine tertiary RNA structures, and if not, why not - is it a lack of interest, or is there a technical barrier? and b) Is there a central repository for RNA structures akin to RCSB PDB database, and if so, where is it located? The only thing I found was RNABase which returns an error and an ugly message saying it has been discontinued.