Evidence for Trans splicing in trypanosomes

The 5′ ends of trypanosome mRNAs consist of an identical sequence of 35 nucleotides. This “mini-exon” sequence is derived from the 5′ end of a 137 nucleotide RNA (medRNA). The remainder of each mRNA is derived from a protein-coding exon that is not linked to the mini-exon. We propose that medRNA is spliced in trans to de-novo-initiated transcripts of protein-coding genes. This trans splicing model predicts that the downstream portion of medRNA will be part of a branched structure and then be released as a free product (minRNA). We demonstrate that significant levels of minRNA exist in trypanosome RNA. Furthermore, minRNA can be released from high molecular weight RNA by a HeLa cell S100 “debranching” extract. We conclude that trnas splicing is the physiological process by which mature mRNA molecules are synthesized in trypanosomes.