Trans-splicing in protozoa and helminths.

Trans-splicing is defined as the process whereby exons derived from two separately transcribed RNAs are joined together. In one type of trans-splicing, nuclear pre-mRNAs acquire their 5' terminal exon (the spliced leader) from a small spliced leader RNA (SL RNA) via an RNA processing reaction that is directly analagous to the removal of intervening sequences (cis-splicing). Such leader-addition by trans-splicing has been extensively studied in trypanosomatid protozoans and in nematodes. This review summarizes recent advances in research on trans-splicing in these two systems. Progress in elucidating functionally significant sequence elements within SL RNAs and progress in understanding the mechanism and biological role of trans-splicing is discussed.