Direct analysis of the mini-exon donor RNA of Trypanosoma brucei: detection of a novel cap structure also present in messenger RNA.
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.
D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D005091:Exons; D009693:Nucleic Acid Hybridization; D009841:Oligonucleotides / Q000235:genetics; D012313:RNA / Q000096:biosynthesis / Q000235:genetics*; D012315:RNA Caps / Q000302:isolation & purification*; D012333:RNA, Messenger / Q000235:genetics*; D012260:Ribonucleases / Q000302:isolation & purification; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism
D009841:Oligonucleotides; D012315:RNA Caps; D012333:RNA, Messenger; D012313:RNA; D012260:Ribonucleases