[
Wiley Interdiscip Rev RNA,
2011]
Trans-splicing is the joining together of portions of two separate pre-mRNA molecules. The two distinct categories of spliceosomal trans-splicing are genic trans-splicing, which joins exons of different pre-mRNA transcripts, and spliced leader (SL) trans-splicing, which involves an exon donated from a specialized SL RNA. Both depend primarily on the same signals and components as cis-splicing. Genic trans-splicing events producing protein-coding mRNAs have been described in a variety of organisms, including Caenorhabditis elegans and Drosophila. In mammalian cells, genic trans-splicing can be associated with cancers and translocations. SL trans-splicing has mainly been studied in nematodes and trypanosomes, but there are now numerous and diverse phyla (including primitive chordates) where this type of trans-splicing has been detected. Such diversity raises questions as to the evolutionary origin of the process. Another intriguing question concerns the function of trans-splicing, as operon resolution can only account for a small proportion of the total amount of SL trans-splicing.
[
Annual Review of Microbiology,
1993]
In nematodes, many mRNAs contain a common 5' terminal 22-nt sequence. This sequence, the spliced leader (SL), is acquired from a small (approximately 100 nt) SL RNA via trans-splicing. Parallel in vitro and in vivo experiments have begun to clarify both the mechanism and biological role of trans-splicing. In vitro analysis (in cell free extracts) has shown that trans-splicing is remarkably similar to the snRNP mediated removal of intervening sequences from pre-mRNAs (cis-splicing). Additionally, this analysis has suggested a mechanism that may explain how the two substrates of trans-splicing (the SL RNA and pre-mRNA) efficiently associate with one another in the absence of sequence complementarity. In vivo experiments suggest that a major biological function of trans-splicing in nematodes may be to process polycistronic transcription units. Results obtained from the study of both parasitic and free-living species are discussed, and trans-splicing in nematodes is compared and contrasted to the analogous process in trypanosomatid protozoans.
[
BioEssays,
1993]
In trans-splicing, the pre-mRNA products of two different genes are spliced together to form a single, mature mRNA. In one type of trans-splicing, pre-mRNAs of many different genes receive a single, short leader, called spliced leader or SL. This type of trans-splicing was first discovered in the primitive eukaryotes, the trypanosomes, where it is apparently the only kind of nuclear mRNA splicing. Subsequently, it was discovered in nematodes (round worms), trematodes (flat worms), and euglena. Although this type of trans-splicing has never been found in any of the other well-studied organisms, Bruzik and Maniatis have recently reported that mammalian cells are capable of performing the reaction when they are provided with the appropriate pre-mRNAs.