Valverde J R, Marco R, Garesse R
Departamento de Bioquímica, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Proc Natl Acad Sci U S A. 1994 Jun 7;91(12):5368-71. doi: 10.1073/pnas.91.12.5368.
A search of sequence data bases for a tridecamer transcription termination signal, previously described in human mtDNA as being responsible for the accumulation of mitochondrial ribosomal RNAs (rRNAs) in excess over the rest of mitochondrial genes, has revealed that this termination signal occurs in equivalent positions in a wide variety of organisms from protozoa to mammals. Due to the compact organization of the mtDNA, the tridecamer motif usually appears as part of the 3' adjacent gene sequence. Because in phylogenetically widely separated organisms the mitochondrial genome has experienced many rearrangements, it is interesting that its occurrence near the 3' end of the large rRNA is independent of the adjacent gene. The tridecamer sequence has diverged in phylogenetically widely separated organisms. Nevertheless, a well-conserved heptamer--TGGCAGA, the mitochondrial rRNA termination box--can be defined. Although extending the experimental evidence of its role as a transcription termination signal in humans will be of great interest, its evolutionary conservation strongly suggests that mitochondrial rRNA transcription termination could be a widely conserved mechanism in animals. Furthermore, the conservation of a homologous tridecamer motif in one of the last 3' secondary loops of nonmitochondrial 23S-like rRNAs suggests that the role of the sequence has changed during mitochondrial evolution.
在序列数据库中搜索一种十三聚体转录终止信号，该信号先前在人类线粒体DNA中被描述为导致线粒体核糖体RNA（rRNA）相对于其他线粒体基因过量积累的原因，结果显示这种终止信号在从原生动物到哺乳动物的多种生物的等效位置出现。由于线粒体DNA的紧凑组织，十三聚体基序通常作为3'相邻基因序列的一部分出现。因为在系统发育上广泛分离的生物中，线粒体基因组经历了许多重排，所以有趣的是它在大rRNA的3'末端附近的出现与相邻基因无关。十三聚体序列在系统发育上广泛分离的生物中已经发生了分歧。然而，可以定义一个高度保守的七聚体——TGGCAGA，即线粒体rRNA终止框。虽然扩展其作为人类转录终止信号作用的实验证据将非常有趣，但其进化保守性强烈表明线粒体rRNA转录终止可能是动物中广泛保守的机制。此外，在非线粒体23S样rRNA的最后一个3'二级环之一中同源十三聚体基序的保守性表明该序列的作用在线粒体进化过程中发生了变化。
