Freistadt M S, Cross G A, Branch A D, Robertson H D
Laboratory of Molecular Parasitology, Rockefeller University, New York 10021.
Nucleic Acids Res. 1987 Dec 10;15(23):9861-79. doi: 10.1093/nar/15.23.9861.
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: m7GpppAACUAA*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.
微小外显子是在锥虫mRNA 5'端发现的一小段序列，由一种小RNA即微小外显子供体（medRNA）提供。通过杂交筛选和凝胶电泳从布氏锥虫中纯化出体内经32P标记的medRNA、与其相关的一组较小RNA以及mRNA。利用RNA指纹图谱和测序技术，对微小外显子寡核苷酸进行了鉴定和表征。我们检测到medRNA和mRNA中都存在一种新的5'末端加帽寡核苷酸。该结构包含m7G和至少四个先前未鉴定的修饰核苷酸。如果布氏锥虫微小外显子在其最初指定的5'端上游恰好有四个转录核苷酸，那么它将以序列m7GpppAACUAA*CG（星号表示修饰）开始，并且medRNA将长140个核苷酸，不包括m7G残基。微小外显子包含一种新的5'末端结构，并且在其转移到mRNA的过程中保留该结构，其存在可能赋予独特的功能特性。
