Alternative translation initiation codons for the plastid maturase MatK: unraveling the pseudogene misconception in the Orchidaceae

Background: The plastid maturase MatK has been implicated as a possible model for the evolutionary “missing link” between prokaryotic and eukaryotic splicing machinery. This evolutionary implication has sparked investigations concerning the function of this unusual maturase. Intron targets of MatK activity suggest that this is an essential enzyme for plastid function. The matK gene, however, is described as a pseudogene in many photosynthetic orchid species due to presence of premature stop codons in translations, and its high rate of nucleotide and amino acid substitution. Results: Sequence analysis of the matK gene from orchids identified an out-of-frame alternative AUG initiation codon upstream from the consensus initiation codon used for translation in other angiosperms. We demonstrate translation from the alternative initiation codon generates a conserved MatK reading frame. We confirm that MatK protein is expressed and functions in sample orchids currently described as having a m...背景：质体成熟酶MatK（plastid maturase MatK）被认为是原核与真核生物剪接机制之间进化层面“缺失环节”的潜在模型。这一进化推论引发了针对这种特殊成熟酶功能的相关研究。针对MatK活性的内含子靶标分析表明，该酶是质体功能正常发挥所必需的关键酶类。然而，由于翻译过程中存在提前终止密码子，且其核苷酸与氨基酸替换速率极高，matK基因在诸多光合兰花物种中被归类为假基因。结果：对兰花matK基因的序列分析发现，在其他被子植物翻译所用的共有起始密码子上游，存在一个偏离读码框的备用AUG起始密码子。本研究证实，由该备用起始密码子启动的翻译可产生保守的MatK读码框。我们证实，在目前被描述为含有……（原文此处未完结）的兰花样本中，MatK蛋白能够表达并行使功能。