During the noncanonical deletion transcription, k nucleotides are systematically skipped/deleted after each transcribed trinucleotide producing deletion-RNAs (delRNAs). Peptides matching delRNAs either result from (a) canonical translation of delRNAs; or (b) noncanonical translation of regular transcripts along expanded codons. Only along frame "0" (start site) (a) and (b) produce identical peptides. Here, mitochondrial mass spectrometry data analyses assume expanded codon/del-transcription with 3 + k (k from 0 to 12) nucleotides. Detected peptides map preferentially on previously identified delRNAs. More peptides were detected for k (1–12) when del-transcriptional and expanded codon translations start sites coincide (i.e. the 0^th frame) than for frames +1 or +2. Hence, both (a) and (b) produced peptides identified here. Biases for frame 0 decrease for k > 2, reflecting codon/anticodon expansion limits. Further analyses find preferential pyrrolysine insertion at stop codons, suggesting Pyl-specific mitochondrial suppressor tRNAs loaded by Pyl-specific tRNA synthetases with unknown origins. Pyl biases at stops are stronger for regular than expanded codons suggesting that Pyl-tRNAs are less competitive with near-cognate tRNAs in expanded codon contexts. Statistical biases for these findings exclude that detected peptides are experimental and/or bioinformatic artefacts implying both del-transcription and expanded codons translation occur in human mitochondria.

在非规范性缺失转录过程中，每个转录的三核苷酸产生缺失RNA（delRNA）后，系统地跳过/删除k个核苷酸。匹配delRNA的肽要么来自（a）delRNA的规范翻译；或（b）常规密码本沿扩展密码子的非规范翻译。仅沿着框架“ 0”（起始位点）（a）和（b）产生相同的肽。在这里，线粒体质谱数据分析假定扩展的密码子/ del转录具有3 + k（k从0到12）个核苷酸。检测到的肽优先定位在先前鉴定的delRNA上。当del转录和扩展的密码子翻译起始位点重合时（即第0^位），检测到更多的k（1-12）肽段。帧），而不是帧+1或+2。因此，（a）和（b）均产生了此处鉴定的肽。框架0的偏差在k> 2时减小，反映了密码子/反密码子扩展极限。进一步的分析发现在终止密码子上优先插入了吡咯赖氨酸，这表明由Pyl特异性tRNA合成物加载的Pyl特异性线粒体抑制性tRNA来源不明。规则密码子在终止时的Pyl偏向性强于扩展密码子，这表明在扩展密码子环境中，Pyl-tRNA与近同源tRNA的竞争性较低。这些发现的统计偏倚不包括检测到的肽是实验性和/或生物信息性伪像，这暗示了人类线粒体中同时发生了del转录和扩展的密码子翻译。