Selection of the 3'-splice site in group I introns.

A model for selection of 3'-splice sites in splicing of RNA precursors containing group I introns is presented. The key feature of this model is a newly identified tertiary interaction between the catalytic core of the intron and the 3'-splice site. This tertiary pairing would bring the 3'-splice site into the core of the intron, which is known to contain RNA sequences and structures essential for catalyzing the splicing reactions. The proposed tertiary interaction can coexist with P10, a pairing between 3'-exon sequences and the 'internal guide sequence' near the 5'-end of the intron. The model predicts that three RNA-RNA interactions are important in selection of 3'-splice sites: (i) binding of intron sequences with the core; (ii) pairing of exon sequences with the internal guide sequence; and (iii) binding of the terminal guanosine to an unknown site within the core.