Reichert A S, Mörl M
Max-Planck-Institute for Evolutionary Anthropology, Inselstrasse 22, 04103 Leipzig, Germany.
Nucleic Acids Res. 2000 May 15;28(10):2043-8. doi: 10.1093/nar/28.10.2043.
The integrity of 3'-ends of tRNAs is essential for aminoacylation and consequently for protein synthesis. The CCA-termini are generated and, if truncated by exonucleolytic activity, restored by tRNA nucleotidyltransferase. However, further truncations at the 3'-end can occur by exonuclease activity or during processing of overlapping tRNA primary transcripts in metazoan mitochondria. In the latter case, the upstream tRNA is released in a 3'-truncated form (lacking up to six bases) and subsequently completed. In human mitochondria, tRNA(Tyr)(missing the discriminator nucleotide A(73)) is completed by a discriminator adding activity followed by CCA addition. Since in vivo a high percentage of further 3'-terminally degraded human tRNA(Tyr)transcripts could be observed, it was tested in an in vitro system whether this repair mechanism for tRNA 3'-ends acts also on these further degraded tRNA versions. Additionally, 3'-truncated versions of two non-overlapping mitochondrial tRNAs (tRNA(Thr)and tRNA(Phe)) were examined. The results show that these transcripts can be repaired during incubation. A similar base incorporating activity was observed in mouse mitochondria, indicating that a repair mechanism for the 3'-end of several tRNAs exists in mitochondria of humans and possibly other metazoans which goes beyond the CCA addition.
tRNA 3'末端的完整性对于氨酰化作用至关重要，因此对于蛋白质合成也至关重要。CCA末端是生成的，如果被核酸外切酶活性截断，则由tRNA核苷酸转移酶恢复。然而，3'末端的进一步截断可通过核酸外切酶活性或在后生动物线粒体中重叠tRNA初级转录本的加工过程中发生。在后一种情况下，上游tRNA以3'截断的形式释放（最多缺少六个碱基），随后完成。在人类线粒体中，tRNA(Tyr)（缺少判别核苷酸A(73)）通过判别添加活性随后添加CCA来完成。由于在体内可以观察到高比例的进一步3'末端降解的人类tRNA(Tyr)转录本，因此在体外系统中测试了这种tRNA 3'末端的修复机制是否也作用于这些进一步降解的tRNA版本。此外，还检查了两种非重叠线粒体tRNA（tRNA(Thr)和tRNA(Phe)）的3'截断版本。结果表明，这些转录本在孵育过程中可以被修复。在小鼠线粒体中观察到类似的碱基掺入活性，表明在人类以及可能其他后生动物的线粒体中存在一种针对几种tRNA 3'末端的修复机制，该机制超出了CCA添加的范围。
