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首页> 外文期刊>Journal of bacteriology >The Trimethylamine Methyltransferase Gene and Multiple Dimethylamine Methyltransferase Genes of Methanosarcina barkeri Contain In-Frame and Read-Through Amber Codons
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The Trimethylamine Methyltransferase Gene and Multiple Dimethylamine Methyltransferase Genes of Methanosarcina barkeri Contain In-Frame and Read-Through Amber Codons

机译:巴氏甲烷八叠球菌的三甲胺甲基转移酶基因和多个二甲胺甲基转移酶基因含有框内和直读琥珀色密码子

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Three different methyltransferases initiate methanogenesis from trimethylamine (TMA), dimethylamine (DMA) or monomethylamine (MMA) by methylating different cognate corrinoid proteins that are subsequently used to methylate coenzyme M (CoM). Here, genes encoding the DMA and TMA methyltransferases are characterized for the first time. A single copy of mttB, the TMA methyltransferase gene, was cotranscribed with a copy of the DMA methyltransferase gene,mtbB1. However, two other nearly identical copies ofmtbB1, designated mtbB2 and mtbB3, were also found in the genome. A 6.8-kb transcript was detected with probes to mttB and mtbB1, as well as tomtbC and mttC, encoding the cognate corrinoid proteins for DMA:CoM and TMA:CoM methyl transfer, respectively, and with probes to mttP, encoding a putative membrane protein which might function as a methylamine permease. These results indicate that these genes, found on the chromosome in the ordermtbC, mttB, mttC, mttP, and mtbB1, form a single transcriptional unit. A transcriptional start site was detected 303 or 304 bp upstream of the translational start of mtbC. The MMA, DMA, and TMA methyltransferases are not homologs; however, like the MMA methyltransferase gene, the genes encoding the DMA and TMA methyltransferases each contain a single in-frame amber codon. Each of the three DMA methyltransferase gene copies from Methanosarcina barkeri contained an amber codon at the same position, followed by a downstream UAA or UGA codon. The C-terminal residues of DMA methyltransferase purified from TMA-grown cells matched the residues predicted for the gene products of mtbB1,mtbB2, or mtbB3 if termination occurred at the UAA or UGA codon rather than the in-frame amber codon. ThemttB gene from Methanosarcina thermophilacontained a UAG codon at the same position as the M. barkeri mttB gene. The UAG codon is also present in mttBtranscripts. Thus, the genes encoding the three types of methyltransferases that initiate methanogenesis from methylamine contain in-frame amber codons that are suppressed during expression of the characterized methyltransferases.
机译:三种不同的甲基转移酶通过甲基化不同的同源皮质类固醇蛋白使三甲胺(TMA),二甲基胺(DMA)或单甲胺(MMA)引发甲烷生成,随后将其用于甲基化辅酶M(CoM)。在此,首次表征了编码DMA和TMA甲基转移酶的基因。将TMA甲基转移酶基因 mttB 的单个副本与DMA甲基转移酶基因 mtbB1 的副本共转录。但是,在基因组中还发现了另外两个 mtbB1 几乎相同的副本,分别称为 mtbB2 mtbB3 。使用 mttB mtbB1 以及 mtbC mttC 的探针检测到6.8-kb的转录本,分别编码用于DMA:CoM和TMA:CoM甲基转移的同源类海rin蛋白,并带有 mttP 的探针,编码可能用作甲胺通透酶的假定膜蛋白。这些结果表明,这些基因以 mtbC mttB mttC mttP ,和 mtbB1 ,形成一个转录单元。在 mtbC 的翻译起始位点上游303或304 bp处检测到一个转录起始位点。 MMA,DMA和TMA甲基转移酶不是同源物;但是,与MMA甲基转移酶基因一样,编码DMA和TMA甲基转移酶的基因每个都包含一个单一的框内琥珀密码子。来自 Methanosarcina barkeri 的三个DMA甲基转移酶基因拷贝中的每一个都在相同位置包含一个琥珀色密码子,随后是一个下游UAA或UGA密码子。从TMA生长的细胞中纯化的DMA甲基转移酶的C末端残基与 mtbB1 mtbB2 mtbB3 的基因产物预测的残基匹配如果终止发生在UAA或UGA密码子而不是框架内琥珀色密码子。 嗜热甲烷球菌 mttB 基因在与 M相同的位置包含一个UAG密码子。 barkeri mttB 基因。 UAG密码子也存在于 mttB 抄本中。因此,编码从甲胺引发甲烷生成的三种类型的甲基转移酶的基因含有框内琥珀密码子,该密码子在表征的甲基转移酶的表达过程中被抑制。

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