Folding and catalysis by the VS ribozyme.

The VS ribozyme is a 154 nt self-cleaving RNA molecule that can be divided into a trans-acting five-helix ribozyme and stem-loop substrate. The structure of the ribozyme is organised by two three-way helical junctions, the structure of which has been determined by a combination of comparative gel electrophoresis and fluorescence resonance energy transfer experiments. From this, the overall global architecture of the ribozyme has been deduced. The substrate is then thought to dock into the cleft formed between helices II and VI, where it makes a close interaction with the loop containing A730. The A730 loop is the probable active site of the ribozyme, and A756 within it is a strong candidate to play a direct role in the transesterification chemistry, possibly by general acid-base catalysis.