The eucaryal tRNA splicing endonuclease recognizes a tripartite set of RNA elements

The tRNA splicing endonuclease cleaves intron-containing tRNA precursors on both sides of the intron. The prevailing belief has been that the enzyme binds only to the mature domain through the invariant bases. We show instead that, for recognition, the endonuclease utilizes distinct sets of structural elements, several of which are within the intron. One subset of recognition elements, localized in the mature domain, is needed for recognition of both cleavage sites, while two other subsets, localized at the exon-intron boundaries, are used for recognition of either one or the other cleavage site. The two cleavage sites are essentially independent: neither is required by the other for cleavage to take place. These results support a two-active-site model for the eucaryal endonuclease.