Some RNAs Are Self-Splicing

In 1982, Tom Cech discovered that when the pre-rRNA of the protozoan Tetrahymena was incubated with Mg2+ and guanosine monophosphate, splicing of the RNA occurred without the involvement of any protein. This ability of RNA to carry out its own splicing has given rise to the term ribozyme.  

The mechanism of self-splicing in this case is somewhat different from that observed in the spliceosome reaction (fig. 28.21). First the 3 hydroxyl group of the guanosine cofactor attacks the phosphodiester bond at the 5 splice site. This is followed by another transesterification reaction in which the 3 hydroxyl group of the upstream RNA attacks the phosphodiester bond at the 3 splice site, thereby completing the splicing reaction. The final reaction products include the spliced rRNA and the excised oligonucleotide. 

Since its initial discovery, self-splicing has been found to occur for RNAs from a wide variety of organisms. Certain precursor RNAs that exhibit self-splicing produce lariats, just like those seen in the commonly observed splicing reactions that are catalyzed by spliceosomes (see fig. 28.19). These findings suggest that at one time all splicing reactions were RNA-catalyzed. 

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Some RNAs Function Like Enzymes Some RNAs Are Self-Splicing Some Ribonucleases Are RNAs Ribosomal RNA Catalyzes Peptide Bond Formation Catalytic RNA May Have Evolutionary Significance Inhibitors of RNA Metabolism... 

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