Feagin J E, Stuart K
Seattle Biomedical Research Institute, Washington 98109-1651.
Mol Cell Biol. 1988 Mar;8(3):1259-65. doi: 10.1128/mcb.8.3.1259-1265.1988.
The mitochondrial respiratory system is absent in slender bloodstream forms of Trypanosoma brucei, incomplete in stumpy bloodstream forms, and complete in procyclic (insect) forms. The steady-state abundance of transcripts of some mitochondrially encoded components of the respiratory system correlates with its differential expression in different life cycle stages. Recently, it was reported that uridines which are not encoded in the genome are added to cytochrome b and cytochrome oxidase II transcripts. We now report that the (U)+ transcripts of both genes are found in procyclic forms and to some degree in stumpy forms but are absent in slender forms. The uridine additions to cytochrome oxidase II correct a frameshift in the gene and presumably allow production of a full-length protein, whereas those added to cytochrome b create an in-frame AUG which extends the N terminus of the predicted protein by 20 amino acids. The stage specificity of uridine additions to these transcripts thus reflects the life cycle stage during which the protein products would be used. Transcripts of MURF2, a gene of unknown function, have additional uridines in both slender and procyclic forms which create two in-frame AUGs. MURF2 transcripts additionally differ from the DNA sequence in ways which cannot be explained by uridine addition alone, implying that other processes alter these transcripts.
线粒体呼吸系统在布氏锥虫的细长血流形式中不存在，在粗短血流形式中不完整，而在前期（昆虫）形式中是完整的。呼吸系统中一些线粒体编码成分的转录本的稳态丰度与其在不同生命周期阶段的差异表达相关。最近，有报道称基因组中未编码的尿苷被添加到细胞色素b和细胞色素氧化酶II的转录本中。我们现在报告，这两个基因的（U）+转录本在前期形式中存在，在某种程度上在粗短形式中也存在，但在细长形式中不存在。添加到细胞色素氧化酶II的尿苷纠正了该基因中的移码，推测允许产生全长蛋白质，而添加到细胞色素b的尿苷产生了一个框内AUG，使预测蛋白质的N末端延伸了20个氨基酸。因此，这些转录本上尿苷添加的阶段特异性反映了蛋白质产物将被使用的生命周期阶段。MURF2是一个功能未知的基因，其转录本在细长形式和前期形式中都有额外的尿苷，这些尿苷产生了两个框内AUG。MURF2转录本与DNA序列的差异方式不能仅用尿苷添加来解释，这意味着其他过程会改变这些转录本。
