Magnesium chelatase chlIDH and cobalt chelatase cobNST enzymes are required for biosynthesis of (bacterio)chlorophyll and cobalamin (vitamin B12), respectively. Each enzyme consists of large, medium, and small subunits. Structural and primary sequence similarities indicate common evolutionary origin of the corresponding subunits. It has been reported earlier that some of vitamin B12 synthesizing organisms utilized unusual cobalt chelatase enzyme consisting of a large cobalt chelatase subunit (cobN) along with a medium (chlD) and a small (chlI) subunits of magnesium chelatase. In attempt to understand the nature of this phenomenon, we analyzed >1,200 diverse genomes of cobalamin and/or chlorophyll producing prokaryotes. We found that, surprisingly, genomes of many cobalamin producers contained cobN and chlD genes only; a small subunit gene was absent. Further on, we have discovered a diverse group of chlD genes with functional programed ribosomal frameshifting signals. Given a high similarity between the small subunit and the N-terminal part of the medium subunit, we proposed that programed translational frameshifting may allow chlD mRNA to produce both subunits. Indeed, in genomes where genes for small subunits were absent, we observed statistically significant enrichment of programed frameshifting signals in chlD genes. Interestingly, the details of the frameshifting mechanisms producing small and medium subunits from a single chlD gene could be prokaryotic taxa specific. All over, this programed frameshifting phenomenon was observed to be highly conserved and present in both bacteria and archaea.

中文翻译：

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通过编程移码可从单个chlD基因产生两个钴螯合酶亚基。

镁螯合酶chlIDH和钴螯合酶cobNST酶分别是（细菌）叶绿素和钴胺素（维生素B12）的生物合成。每种酶均由大，中和小亚基组成。结构和一级序列的相似性表明相应亚基的共同进化起源。早先有报道说，一些合成维生素B12的生物体利用了不寻常的钴螯合酶，该酶由一个大的钴螯合酶亚基（cobN）以及一个中等的（chlD）和一个小的（chlI）镁螯合酶的亚基。为了了解这种现象的性质，我们分析了钴胺素和/或产生叶绿素的原核生物的1,200多个不同基因组。令人惊讶的是，我们发现许多钴胺素生产者的基因组仅包含cobN和chlD基因。没有一个小的亚基基因。进一步地，我们发现了具有功能性编程核糖体移码信号的各种chlD基因。鉴于小亚基和中等亚基的N端部分之间的相似度很高，我们建议程序化翻译移码可以允许chlD产生两个亚基的mRNA。确实，在缺少小亚基基因的基因组中，我们观察到了chlD基因中编程移码信号的统计学显着富集。有趣的是，由单个chlD基因产生中小亚基的移码机制的细节可能是原核生物分类群特异性的。到处可见，这种程序化的移码现象是高度保守的，并存在于细菌和古细菌中。