Ribozymes

In most cases, proteins called enzymes (or abzymes-see here) catalyze chemical reactions. It turns out, however, that some RNA molecules, called ribozymes are capable of catalyzing chemical reactions too. Figure 11.29 shows the site of action of the RNA-protein complex called ribonuclease P. The RNA portion of the complex can, by itself, catalyze the hydrolysis of the specific bond indicated by the red wedge in the figure.

Tom Cech identified an interesting protein-independent self-splicing agent from the preribosomal RNA of the protist, Tetrahymena. In this reaction, the rRNA itself catalyzes removal of an RNA intron from itself. The RNA molecule involved in the catalysis is altered, so it is not technically considered a catalyst, but the sequence which is removed (called L-19 IVS) does have true catalytic activity. It can either lengthen or shorten small oligonucleotides, in the manner shown in Figure 11.30.

RNAs can catalyze reactions in which evolution of more efficient molecules based on selection can occur. Such processes may have been of importance in a pre-protein world during the origin of life.

1. Ribozyme Enzymology