The trimethylamine methyltransferase gene and multiple dimethylamine methyltransferase genes of Methanosarcina barkeri contain in-frame and read-through amber codons
The trimethylamine methyltransferase gene and multiple dimethylamine methyltransferase genes of Methanosarcina barkeri contain in-frame and read-through amber codons
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DOI：
10.1128/jb.182.9.2520-2529.2000
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发表时间：
2000-05-01
影响因子：
3.2
通讯作者：
Krzycki, JA
中科院分区：
文献类型：
--
作者：
Paul, L;Ferguson, DJ;Krzycki, JA
三种不同的甲基转移酶通过甲基甲基甲基甲基甲基胺（MMA）从三甲胺（TMA），二甲胺（DMA）或单甲胺（MMA）启动甲烷发生，随后用于甲基甲酸盐酶M（COM）。在这里，编码DMA和TMA甲基转移酶的基因首次表征。用DMA甲基转移酶基因MTBB1的副本共转录MTTB的单一副本TMA甲基转移酶基因。但是，在基因组中也发现了另外两个几乎相同的MTBB1副本，指定为MTBB2和MTBB3。用对MTTB和MTBB1的探针以及MTBC和MTTC检测到6.8-Kb转录本，分别编码DMA和TMA的同源类蛋白：COM和TMA：COM甲基转移，以及探针，以及对MTTP的探测蛋白质可能充当甲胺粘酶。这些结果表明，在MTBC，MTTB，MTTC，MTTP和MTBB1的染色体上发现的这些基因形成单个转录单元。检测到MTBC翻译起点上游的303或304 bp的转录启动位点。 MMA DMA和TMA甲基转移酶不是同源物。但是，像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架内琥珀色密码子。来自甲烷核酸菌的三个DMA甲基转移酶基因拷贝中的每一个都在同一位置包含一个琥珀色密码子，然后是下游UAA或UGA密码子，DMA甲基转移酶的C末端残基从TMA生长的细胞中纯化的TMA生长细胞纯化了基因的残基，该残基与该基因相匹配。 MTBB1，MTBB2或MTBB3的产物如果发生在UAA或UGA密码子，而不是框架内琥珀色密码子。来自甲烷菌的MTTB基因在与Barkeri M. barkeri MTTB基因相同的位置中包含一个UAG密码子。 UAG密码子也存在于MTTB转录本中。因此，编码从甲胺中引发甲烷生成的三种类型的甲基转移酶的基因含有框架内琥珀色密码子，这些密码子在表达表达的甲基转移酶表达过程中被抑制。
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 of mtbB1, 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 to mtbC 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 order mtbC, 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. The mttB gene from Methanosarcina thermophila contained a UAG codon at the same position as the M. barkeri mttB gene. The UAG codon is also present in mttB transcripts. 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.