Spliced leader trans-splicing

What is spliced leader (SL) trans -splicing? It is an mRNA maturation process, similar to intron splicing, which has been shown to occur in a limited number of eukaryotes. In SL trans-splicing, the cell replaces nucleotides at the 5' end of some pre-mRNAs with those of a special class of small nuclear RNAs, called SL RNAs. These are short molecules with two functionally distinct halves: the 5' half consists of the leader sequence that is transferred to a pre-mRNA, along with the SL RNA's methylguanosine cap; the 3' half contains a binding site for the Sm protein complex, which binds many of the RNAs involved in intron splicing. These two halves are separated by a splice donor site, a GT dinucleotide. Nuclear machinery trans-splices the leader sequence to splice acceptor sites (AG dinucleotides) in the 5' region of target pre-mRNAs. As a result, many mRNAs in SL trans-splicing species have a common sequence at the 5' end.