Splicing internal guide sequence

The RNA world hypothesis requires a nucleotide polymer to reproduce itself. Can a ribozyme bring about its own synthesis in a template-directed manner The self-splicing rRNA intron of Tetrahymena (Fig. 26-26) catalyzes the reversible attack of a guanosine residue on the 5 splice junction (Fig. 26-37). If the 5 splice site and the internal guide sequence are removed from the intron, the rest of the intron can bind RNA strands paired with short oligonucleotides. Part of the remaining intact intron effectively acts as a template for the... 

The sequence shown is for the Tetrahymena thermophila pre-tRNA. Exons and introns are shown in normal and bold letters respectively. The internal guide sequence (boxed) forms base pair with both exons to form a precise alignment structure for RNA splicing. Similar structures can be drawn for most of group I intervening sequences. 

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