Minihelix-loop RNAs: minimal structures for aminoacylation catalysts.

We report here an in vitro selected ribozyme, KL17, which is active in charging amino acids on its own 5'-OH group. The ribozyme consists of two catalytic domains, one of which (consisting of P5/P6/L6) recognizes amino acid substrates based on the steric environment of the side chain, whereas the other recognizes an aminoacylated oligonucleotide. The secondary structure of this ambidextrous ribozyme arranges into a pseudoknot, where L6 docks onto the 3'-terminal single-stranded region. The formation of this pseudoknot structure brings the P6 region, in which the essential catalytic core is most likely embedded, into the proximity of the 5'-OH group. Our studies show that the P6-L6 domain can be separated from the main body of KL17 and the derived P6-L6 minihelix-loop RNA can act as a trans-aminoacylation catalyst. In this report, we also compare this ribozyme with an analogous aminoacylation system previously characterized in our laboratory and illuminate the similarities and differences between these catalytic systems.