Repair of tRNAs in metazoan mitochondria.
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.
Reichert
A S
AS
Max-Planck-Institute for Evolutionary Anthropology, Inselstrasse 22, 04103 Leipzig, Germany.
Mörl
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D020413:3' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016133:Polymerase Chain Reaction; D012360:RNA, Transfer, Phe / Q000235:genetics*; D012363:RNA, Transfer, Thr / Q000235:genetics*; D012365:RNA, Transfer, Tyr / Q000235:genetics*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D020413:3' Untranslated Regions; D012360:RNA, Transfer, Phe; D012363:RNA, Transfer, Thr; D012365:RNA, Transfer, Tyr