Higher eukaryotes contain a minor class of introns which are spliced by a novel spliceosome (the U12-dependent spliceosome) which differs from the U2-dependent spliceosome, responsible for removal of the majority of introns. The minor class of introns are called U12-dependent introns or AT-AC introns as many of them contain AT and AC as 5' and 3' splice sites respectively, although some contain the normal GT and AG combination. AT-AC introns also differ in the sequence and position of their branchpoints.

The U12-dependent spliceosome contains U11, U12, U4atac and U6atac snRNPs instead of the normal U1, U2, U4 and U6 snRNPs. U5snRNP is common to both U2- and U12-dependent spliceosomes.

In collaboration with Professor Artur Jarmolowski, University of Poznan, Poland, we analysed the splicing efficiency of plant pre-mRNAs containing AT-AC introns (CBP20, GSH and Ld). We found evidence that the 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. A major determinant for high splicing efficiency in the LD U12 intron was the presence of the upstream exon sequence. We are investigating the possible exon splicing enhancers located within this exon.

Kmieciak et al. (2002) Gene 283, 171-183.
Lewandowska et al. (2004) Plant Cell 16, 1340-1352.
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