Determinants of plant U12-dependent intron splicing efficiency.

Factors affecting splicing of plant U12-dependent introns have been examined by extensive mutational analyses in an in vivo tobacco (Nicotiana tabacum) protoplast system using introns from three different Arabidopsis thaliana genes: CBP20, GSH2, and LD. The results provide evidence that splicing efficiency of plant U12 introns depends on a combination of factors, including UA content, exon bridging interactions between the U12 intron and flanking U2-dependent introns, and exon splicing enhancer sequences (ESEs). Unexpectedly, all three plant U12 introns required an adenosine at the upstream purine position in the branchpoint consensus UCCUURAUY.