Discontinuous transcription; the formation of a chimeric mRNA from two transcripts of unlinked loci. trans-Splicing, as distinct from cis-splicing, the more familiar process of excision of introns from pre-mRNA, is common in trypanosomes. An untranslated sequence at the 5΄ end of the mature trypanosome mRNA is a transcript of a tandemly repeated mini-exon and is termed mini-exon-derived RNA (medRNA). It is ligated to a transcript of the coding sequence by displacement of a mini-intron (minRNA) at the 5΄ end in a process mechanistically akin that of cis-splicing.