Exon trans-splicing

Removal of introns Maturation of eukaryotic mRNA usually involves the removal of RNA sequences, which do not code for protein (introns, or intervening sequences) from the primary tran script. The remaining coding sequences, the exons, are spliced together to form the mature mRNA. The molecular machine that accomplishes these tasks is known as the spliceosome. [Note A few eukaryotic primary transcripts contain no introns. Others con tain a few introns, whereas some, such as the primary transcripts for the a-chains of collagen, contain more than fifty intervening sequences that must be removed before mature mRNA is ready for translation.]... 

Spliced leader RNA trans-splicing is a form of RNA editing in which a short RNA exon (the... 

Surprisingly, exon sequences (the 22 nt SL) are irrelevant for SL RNA function in trans-splicing in vitro (36). The fact that the 22 nt SL was not important for SL RNA participation in trans-splicing was not anticipated since this sequence has been stringently conserved in evolutionarily distant nematodes. However, this sequence conservation can be explained in part by the fact that at the DNA level, the SL sequence itself is a promoter element essential for SL RNA synthesis by RNA polymerase II (see above). 

Vellard, M., Sureau, A., Soret, J., Martinerie, C. Perbal, B. (1992) Proc. Natl. Acad. Sci. USA 89, 2511 -2515. A potencial splicing factor is encoded by the oposite strand of the frara-spliced c- myb exon. Breen, M.A. Ashcroft, S.J.H. (1997) FEBSLett. 409, 375-379. A truncated isoform of Ca /calmod-ulin-dependent protein kinase 11 expressed in human islets of Langerhand may result from trans-splicing. 

The three exons of psaA are far apart on the chloroplast genome of C. reinhardtii with exon 1 and exon 2 oriented in opposite direction (10,20, fig. 1). This rules out that the psaA mRNA could result from the processing of a large continuous chloroplast transcript. The data strongly suggest that this mRNA results from two trans-splicing reactions that fuse the transcripts of exon 1 and exon 2 and those of exon 2 and exon 3. 

Conrad et demonstrated that a c -splice acceptor can act as a trans-spMce acceptor when the 5 donor splice site is not well defined. The fra 5-splicing was dominant over the cw-splicing with a poorly-defined, short, untranslated exon. This is apparently the case shown here. The short, untranslated, poorly-defined exon 1 with 30nt may not be long enough to define intron 1, and it becomes outron-like, which allows trans-splicing and cw-splicing to take place simultaneously. 

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