Finnegan P. M., Brown G. G.
Department of Biology, McGill University, Montreal, Quebec, Canada H3A 1B1.
Plant Cell. 1990 Jan;2(1):71-83. doi: 10.1105/tpc.2.1.71.
Relatively little is known about the mechanisms that govern the expression of plant mitochondrial genomes. We have addressed this problem by analyzing the transcriptional activity of different regions of the maize mitochondrial genome using both in vivo and isolated mitochondrial pulse-labeling systems. The regions examined included the protein genes atpA, atp6, and coxII, the 26S, 18S, and 5S rRNA genes, and sequences surrounding the rRNA genes. The rRNAs were found to be transcribed at rates fivefold to 10-fold higher than the protein genes. These rate differences are comparable with the differences in abundance of these species in the total or steady-state RNA population. Pulse-labeled RNA unexpectedly detected transcription of all regions examined, including approximately 21 kilobases of presumed noncoding sequences flanking the rRNA genes for which stable transcripts were not detected. The results obtained with RNA labeled for short pulses in vivo and in isolated mitochondria were similar, suggesting that isolated mitochondria provide a faithful run-on transcription assay. Our results indicate that the absence in total RNA of transcripts homologous to a given region of maize mitochondrial DNA does not necessarily exclude transcriptional activity of that region and that both transcriptional and post-transcriptional processes play important roles in maize mitochondrial genome expression.
关于调控植物线粒体基因组表达的机制，人们了解得相对较少。我们通过使用体内和分离线粒体脉冲标记系统分析玉米线粒体基因组不同区域的转录活性，来解决这个问题。所检测的区域包括蛋白质基因atpA、atp6和coxII，26S、18S和5S rRNA基因，以及rRNA基因周围的序列。发现rRNA的转录速率比蛋白质基因高5到10倍。这些速率差异与这些物种在总RNA群体或稳态RNA群体中的丰度差异相当。脉冲标记的RNA意外地检测到了所有检测区域的转录，包括rRNA基因侧翼约21千碱基的假定非编码序列，而未检测到这些序列的稳定转录本。在体内和分离线粒体中用短脉冲标记RNA得到的结果相似，这表明分离的线粒体提供了一种可靠的连续转录测定方法。我们的结果表明，玉米线粒体DNA特定区域的同源转录本在总RNA中不存在，并不一定排除该区域的转录活性，并且转录和转录后过程在玉米线粒体基因组表达中都起着重要作用。
