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. 1987 Dec 10;15(23):9861–9879. doi: 10.1093/nar/15.23.9861

Direct analysis of the mini-exon donor RNA of Trypanosoma brucei: detection of a novel cap structure also present in messenger RNA.

M S Freistadt 1, G A Cross 1, A D Branch 1, H D Robertson 1
PMCID: PMC306536  PMID: 2447560

Abstract

The mini-exon, a short segment found at the 5' end of trypanosome mRNAs, is contributed by a small RNA, the mini-exon donor (medRNA). In vivo 32P-labeled medRNA, a set of smaller RNAs related to it, and mRNA, were purified from Trypanosoma brucei by hybrid selection and gel electrophoresis. Using RNA fingerprinting and sequencing techniques, mini-exon oligonucleotides were identified and characterized. We detected a novel 5' terminal capped oligonucleotide present in both medRNA and mRNA. This structure contained m7G and at least four modified nucleotides, not identified previously. If the T. brucei mini-exon has exactly four transcribed nucleotides upstream from its originally designated 5' end, it would begin with the sequence: m7GpppA*A*C*U*AA*CG (asterisks denote modification) and medRNA would be 140 nucleotides long, excluding the m7G residue. The mini-exon contains, and retains during its transfer to mRNA, a novel 5' terminal structure whose presence could confer unique functional attributes.

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