RNAseq sequencing of 5 unrelated individuals to study RNA-DNA Differences in Human Mitochondria Restore Ancestral Form of 16S Ribosomal RNA

RNA sequences are generally identical to the underlying DNA sequences but there are known exceptions. These RNA-DNA differences (RDDs) have been found in the nuclear genomes of human cells and in the mitochondria of plants and animals but not in human mitochondria. Here by deep sequencing of DNA and RNA of human mitochondria, we identified 3 RDD sites including an A-to-U and an A-to-G RDD at position 2617. Examination of the precursor polycistronic mitochondrial transcripts shows that the RDD formation occurs post-transcriptionally. Phylogenetic analysis shows that the ancestral allele at position 2617 was a thymine or a guanine. Thus the RDD formation recapitulates the ancestral form of 16S rRNA. Our findings show that RDD formation like other RNA processing steps is conserved across species and likely has functional significance.

RNA序列通常与作为其转录模板的DNA序列保持一致，但已知存在例外情形。这类RNA-DNA差异（RNA-DNA Differences, RDDs）已在人类细胞的核基因组以及动植物的线粒体中被观测到，但尚未在人类线粒体中发现。本研究通过对人类线粒体的DNA与RNA进行深度测序，共鉴定出3个RDD位点，其中2617号位点同时存在A→U型与A→G型RDD。对线粒体多顺反子前体转录本的分析证实，RDD的形成发生在转录后阶段。系统发育分析显示，2617号位点的祖先等位基因为胸腺嘧啶或鸟嘌呤。由此可见，RDD的形成重现了16S核糖体RNA (16S rRNA) 的祖先序列形式。本研究结果表明，与其他RNA加工步骤类似，RDD的形成在各物种间具有保守性，且可能具备重要的生物学功能意义。