Efficient trans-splicing of a yeast mitochondrial RNA group II intron implicates a strong 5' exon-intron interaction.

The reaction mechanism for self-splicing introns requires the existence of a 5' exon binding site on the intron. Experimental evidence is now presented consistent with the existence of such a binding site by demonstrating efficient and accurate trans-self-splicing of a yeast mitochondrial group II intron. Partial and complete trans-splicing reactions take place in the absence of branch formation, part of the usual pathway of nuclear splicing and group II self-splicing. In addition to indicating the existence of a 5' exon binding site on the intron, the results have mechanistic implications for group II self-splicing and perhaps for nuclear splicing as well.