Methyltransferase

14,000,000 Leading Edge Experts on the ideXlab platform

Scan Science and Technology

Contact Leading Edge Experts & Companies

Scan Science and Technology

Contact Leading Edge Experts & Companies

The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Timothy H. Bestor - One of the best experts on this subject based on the ideXlab platform.

  • Methylation of tRNAAsp by the DNA Methyltransferase Homolog Dnmt2
    Science (New York N.Y.), 2006
    Co-Authors: Mary G. Goll, Finn Kirpekar, Steven E Jacobsen, Jeffrey A. Yoder, Keith A. Maggert, Chih-lin Hsieh, Xiaoyu Zhang, Kent G. Golic, Timothy H. Bestor
    Abstract:

    The sequence and the structure of DNA Methyltransferase-2 (Dnmt2) bear close affinities to authentic DNA cytosine Methyltransferases. A combined genetic and biochemical approach revealed that human DNMT2 did not methylate DNA but instead methylated a small RNA; mass spectrometry showed that this RNA is aspartic acid transfer RNA (tRNAAsp) and that DNMT2 specifically methylated cytosine 38 in the anticodon loop. The function of DNMT2 is highly conserved, and human DNMT2 protein restored methylation in vitro to tRNAAsp from Dnmt2-deficient strains of mouse, Arabidopsis thaliana, and Drosophila melanogaster in a manner that was dependent on preexisting patterns of modified nucleosides. Indirect sequence recognition is also a feature of eukaryotic DNA Methyltransferases, which may have arisen from a Dnmt2-like RNA Methyltransferase.

  • A Candidate Mammalian DNA Methyltransferase Related to pmt1p of Fission Yeast
    Human molecular genetics, 1998
    Co-Authors: Jeffrey A. Yoder, Timothy H. Bestor
    Abstract:

    Trace levels of 5-methylcytosine persist in the DNA of mouse embryonic stem cells that are homozygous for null mutations in Dnmt1 , the gene for the one previously recognized metazoan DNA Methyltransferase. This residual 5-methylcytosine may be the product of a candidate second DNA Methyltransferase, Dnmt2, that has now been identified in human and mouse. Dnmt2 contains all the sequence motifs diagnostic of DNA (cytosine-5)-Methyltransferases but appears to lack the large N-terminal regulatory domain common to other eukaryotic Methyltransferases. Dnmt2 is more similar to a putative DNA Methyltransferase of the fission yeast Schizosaccharomyces pombe than to Dnmt1. Dnmt2 produces multiple mRNA species that are present at low levels in all tissues of human and mouse and is not restricted to those cell types known to be active in de novo methylation. The human DNMT2 gene was mapped to chromosome 10p12-10p14 in a panel of radiation hybrids. Dnmt2 is a candidate for the activity that methylates newly integrated retroviral DNA and maintains trace levels of 5-methylcytosine in the DNA of embryonic stem cells homozygous for null mutations in Dnmt1.

  • dna cytosine 5 Methyltransferases in mouse cells and tissues studies with a mechanism based probe
    Journal of Molecular Biology, 1997
    Co-Authors: Jeffrey A. Yoder, Neilesh S Soman, Gregory L Verdine, Timothy H. Bestor
    Abstract:

    The mechanisms that establish and maintain methylation patterns in the mammalian genome are very poorly understood, even though perturbations of methylation patterns lead to a loss of genomic imprinting, ectopic X chromosome inactivation, and death of mammalian embryos. A family of sequence-specific DNA Methyltransferases has been proposed to be responsible for the wave of de novo methylation that occurs in the early embryo, although no such enzyme has been identified. A universal mechanism-based probe for DNA (cytosine-5)-Methyltransferases was used to screen tissues and cell types known to be active in de novo methylation for new species of DNA Methyltransferase. All identifiable de novo Methyltransferase activity was found to reside in Dnmt1. As this enzyme is the predominant de novo Methyltransferase at all developmental stages inspected, it does not fit the definition of maintenance Methyltransferase or hemimethylase. Recent genetic data indicate that de novo methylation of retroviral DNA in embryonic stem cells is likely to involve one or more additional DNA Methyltransferases. Such enzymes were not detected and are either present in very small amounts or are very different from Dnmt1. A new method was developed and used to determine the sequence specificity of intact Dnmt1 in whole-cell lysates. Specificity was found to be confined to the sequence 5′-CpG-3′; there was little dependence on sequence context or density of CpG dinucleotides. These data suggest that any sequence-specific de novo methylation mediated by Dnmt1 is either under the control of regulatory factors that interact with Dnmt1, or is cued by alternative secondary structures in DNA.

  • activation of mammalian dna Methyltransferase by cleavage of a zn binding regulatory domain
    The EMBO Journal, 1992
    Co-Authors: Timothy H. Bestor
    Abstract:

    Mammalian DNA (cytosine-5) Methyltransferase contains a C-terminal domain that is closely related to bacterial cytosine-5 restriction Methyltransferase. This Methyltransferase domain is linked to a large N-terminal domain. It is shown here that the N-terminal domain contains a Zn binding site and that the N- and C-terminal domains can be separated by cleavage with trypsin or Staphylococcus aureus protease V8; the protease V8 cleavage site was determined by Edman degradation to lie 10 residues C-terminal of the run of alternating lysyl and glycyl residues which joins the two domains and six residues N-terminal of the first sequence motif conserved between the mammalian and bacterial cytosine Methyltransferases. While the intact enzyme had little activity on unmethylated DNA substrates, cleavage between the domains caused a large stimulation of the initial velocity of methylation of unmethylated DNA without substantial change in the rate of methylation of hemimethylated DNA. These findings indicate that the N-terminal domain of DNA Methyltransferase ensures the clonal propagation of methylation patterns through inhibition of the de novo activity of the C-terminal domain. Mammalian DNA Methyltransferase is likely to have arisen via fusion of a prokaryotic-like restriction Methyltransferase and an unrelated DNA binding protein. Stimulation of the de novo activity of DNA Methyltransferase by proteolytic cleavage in vivo may contribute to the process of ectopic methylation observed in the DNA of aging animals, tumors and in lines of cultured cells.

Peter W Laird - One of the best experts on this subject based on the ideXlab platform.

  • cpg island hypermethylation in human colorectal tumors is not associated with dna Methyltransferase overexpression
    Cancer Research, 1999
    Co-Authors: Cindy A Eads, Kathleen D Danenberg, Kazuyuki Kawakami, Leonard Saltz, Peter V Danenberg, Peter W Laird
    Abstract:

    The molecular basis of aberrant hypermethylation of CpG islands observed in a subset of human colorectal tumors is unknown. One potential mechanism is the up-regulation of DNA (cytosine-5)-Methyltransferases. Recently, two new mammalian DNA Methyltransferase genes have been identified, which are referred to as DNMT3A and DNMT3B . The encoded proteins differ from the predominant mammalian DNA Methyltransferase DNMT1 in that they have a substantially higher ratio of de novo to maintenance Methyltransferase activity. We have used a highly quantitative 5′ nuclease fluorogenic reverse transcription-PCR method (TaqMan) to analyze the expression of all three DNA Methyltransferase genes in 25 individual colorectal adenocarcinoma specimens and matched normal mucosa samples. In addition, we examined the methylation patterns of four CpG islands [ APC , ESR1 (estrogen receptor), CDKN2A (p16), and MLH1 ] to determine whether individual tumors show a positive correlation between the level of DNA Methyltransferase expression and the frequency of CpG island hypermethylation. All three Methyltransferases appear to be up-regulated in tumors when RNA levels are normalized using either ACTB (β-actin) or POLR2A (RNA pol II large subunit), but not when RNA levels are normalized with proliferation-associated genes, such as H4F2 (histone H4) or PCNA . The frequency or extent of CpG island hypermethylation in individual tumors did not correlate with the expression of any of the three DNA Methyltransferases. Our results suggest that deregulation of DNA Methyltransferase gene expression does not play a role in establishing tumor-specific abnormal DNA methylation patterns in human colorectal cancer.

  • cpg island hypermethylation in human colorectal tumors is not associated with dna Methyltransferase overexpression
    Cancer Research, 1999
    Co-Authors: Cindy A Eads, Kathleen D Danenberg, Kazuyuki Kawakami, Peter V Danenberg, Leonard B Saltz, Peter W Laird
    Abstract:

    The molecular basis of aberrant hypermethylation of CpG islands observed in a subset of human colorectal tumors is unknown. One potential mechanism is the up-regulation of DNA (cytosine-5)-Methyltransferases. Recently, two new mammalian DNA Methyltransferase genes have been identified, which are referred to as DNMT3A and DNMT3B. The encoded proteins differ from the predominant mammalian DNA Methyltransferase DNMT1 in that they have a substantially higher ratio of de novo to maintenance Methyltransferase activity. We have used a highly quantitative 5' nuclease fluorogenic reverse transcription-PCR method (TaqMan) to analyze the expression of all three DNA Methyltransferase genes in 25 individual colorectal adenocarcinoma specimens and matched normal mucosa samples. In addition, we examined the methylation patterns of four CpG islands [APC, ESR1 (estrogen receptor), CDKN2A (p16), and MLH1] to determine whether individual tumors show a positive correlation between the level of DNA Methyltransferase expression and the frequency of CpG island hypermethylation. All three Methyltransferases appear to be up-regulated in tumors when RNA levels are normalized using either ACTB (beta-actin) or POLR2A (RNA pol II large subunit), but not when RNA levels are normalized with proliferation-associated genes, such as H4F2 (histone H4) or PCNA. The frequency or extent of CpG island hypermethylation in individual tumors did not correlate with the expression of any of the three DNA Methyltransferases. Our results suggest that deregulation of DNA Methyltransferase gene expression does not play a role in establishing tumor-specific abnormal DNA methylation patterns in human colorectal cancer.

Steven E Jacobsen - One of the best experts on this subject based on the ideXlab platform.

  • the de novo cytosine Methyltransferase drm2 requires intact uba domains and a catalytically mutated paralog drm3 during rna directed dna methylation in arabidopsis thaliana
    PLOS Genetics, 2010
    Co-Authors: Hang-gyeong Chin, Angelique Deleris, Gregory A Horwitz, Krystyna A Kelly, William Wong, Xuehua Zhong, Sriharsa Pradhan, Ian R Henderson, Steven E Jacobsen
    Abstract:

    Eukaryotic DNA cytosine methylation can be used to transcriptionally silence repetitive sequences, including transposons and retroviruses. This silencing is stable between cell generations as cytosine methylation is maintained epigenetically through DNA replication. The Arabidopsis thaliana Dnmt3 cytosine Methyltransferase ortholog DOMAINS REARRANGED Methyltransferase2 (DRM2) is required for establishment of small interfering RNA (siRNA) directed DNA methylation. In mammals PIWI proteins and piRNA act in a convergently evolved RNA–directed DNA methylation system that is required to repress transposon expression in the germ line. De novo methylation may also be independent of RNA interference and small RNAs, as in Neurospora crassa. Here we identify a clade of catalytically mutated DRM2 paralogs in flowering plant genomes, which in A.thaliana we term DOMAINS REARRANGED Methyltransferase3 (DRM3). Despite being catalytically mutated, DRM3 is required for normal maintenance of non-CG DNA methylation, establishment of RNA–directed DNA methylation triggered by repeat sequences and accumulation of repeat-associated small RNAs. Although the mammalian catalytically inactive Dnmt3L paralogs act in an analogous manner, phylogenetic analysis indicates that the DRM and Dnmt3 protein families diverged independently in plants and animals. We also show by site-directed mutagenesis that both the DRM2 N-terminal UBA domains and C-terminal Methyltransferase domain are required for normal RNA–directed DNA methylation, supporting an essential targeting function for the UBA domains. These results suggest that plant and mammalian RNA–directed DNA methylation systems consist of a combination of ancestral and convergent features.

  • Methylation of tRNAAsp by the DNA Methyltransferase Homolog Dnmt2
    Science (New York N.Y.), 2006
    Co-Authors: Mary G. Goll, Finn Kirpekar, Steven E Jacobsen, Jeffrey A. Yoder, Keith A. Maggert, Chih-lin Hsieh, Xiaoyu Zhang, Kent G. Golic, Timothy H. Bestor
    Abstract:

    The sequence and the structure of DNA Methyltransferase-2 (Dnmt2) bear close affinities to authentic DNA cytosine Methyltransferases. A combined genetic and biochemical approach revealed that human DNMT2 did not methylate DNA but instead methylated a small RNA; mass spectrometry showed that this RNA is aspartic acid transfer RNA (tRNAAsp) and that DNMT2 specifically methylated cytosine 38 in the anticodon loop. The function of DNMT2 is highly conserved, and human DNMT2 protein restored methylation in vitro to tRNAAsp from Dnmt2-deficient strains of mouse, Arabidopsis thaliana, and Drosophila melanogaster in a manner that was dependent on preexisting patterns of modified nucleosides. Indirect sequence recognition is also a feature of eukaryotic DNA Methyltransferases, which may have arisen from a Dnmt2-like RNA Methyltransferase.

  • Conserved plant genes with similarity to mammalian de novo DNA Methyltransferases.
    Proceedings of the National Academy of Sciences of the United States of America, 2000
    Co-Authors: Xiaofeng Cao, Nathan M. Springer, Michael G. Muszynski, Ronald L. Phillips, Shawn M. Kaeppler, Steven E Jacobsen
    Abstract:

    DNA methylation plays a critical role in controlling states of gene activity in most eukaryotic organisms, and it is essential for proper growth and development. Patterns of methylation are established by de novo Methyltransferases and maintained by maintenance Methyltransferase activities. The Dnmt3 family of de novo DNA Methyltransferases has recently been characterized in animals. Here we describe DNA Methyltransferase genes from both Arabidopsis and maize that show a high level of sequence similarity to Dnmt3, suggesting that they encode plant de novo Methyltransferases. Relative to all known eukaryotic Methyltransferases, these plant proteins contain a novel arrangement of the motifs required for DNA Methyltransferase catalytic activity. The N termini of these Methyltransferases contain a series of ubiquitin-associated (UBA) domains. UBA domains are found in several ubiquitin pathway proteins and in DNA repair enzymes such as Rad23, and they may be involved in ubiquitin binding. The presence of UBA domains provides a possible link between DNA methylation and ubiquitin/proteasome pathways.

Kristala L J Prather - One of the best experts on this subject based on the ideXlab platform.

  • development of a vanillate biosensor for the vanillin biosynthesis pathway in e coli
    ACS Synthetic Biology, 2019
    Co-Authors: Aditya M Kunjapur, Kristala L J Prather
    Abstract:

    The engineered de novo vanillin biosynthesis pathway constructed in Escherichia coli is industrially relevant but limited by the reaction catalyzed by catechol O-Methyltransferase, which is intended to catalyze the conversion of protocatechuate to vanillate. To identify alternative O-Methyltransferases, we constructed a vanillate sensor based on the Caulobacter crescentus VanR-VanO system. Using an E. coli promoter library, we achieved greater than 14-fold dynamic range in our best rationally constructed sensor. We found that this construct and an evolved variant demonstrate remarkable substrate selectivity, exhibiting no detectable response to the regioisomer byproduct isovanillate and minimal response to structurally similar pathway intermediates. We then harnessed the evolved biosensor to conduct rapid bioprospecting of natural catechol O-Methyltransferases and identified three previously uncharacterized but active O-Methyltransferases. Collectively, these efforts enrich our knowledge of how biosensing...

  • development of a vanillate biosensor for the vanillin biosynthesis pathway in e coli
    ACS Synthetic Biology, 2019
    Co-Authors: Aditya M Kunjapur, Kristala L J Prather
    Abstract:

    The engineered de novo vanillin biosynthesis pathway constructed in Escherichia coli is industrially relevant but limited by the reaction catalyzed by catechol O-Methyltransferase, which is intended to catalyze the conversion of protocatechuate to vanillate. To identify alternative O-Methyltransferases, we constructed a vanillate sensor based on the Caulobacter crescentus VanR-VanO system. Using an E. coli promoter library, we achieved greater than 14-fold dynamic range in our best rationally constructed sensor. We found that this construct and an evolved variant demonstrate remarkable substrate selectivity, exhibiting no detectable response to the regioisomer byproduct isovanillate and minimal response to structurally similar pathway intermediates. We then harnessed the evolved biosensor to conduct rapid bioprospecting of natural catechol O-Methyltransferases and identified three previously uncharacterized but active O-Methyltransferases. Collectively, these efforts enrich our knowledge of how biosensing can aid metabolic engineering and constitute the foundation for future improvements in vanillin pathway productivity.

Joseph A Krzycki - One of the best experts on this subject based on the ideXlab platform.

  • RamA, a Protein Required for Reductive Activation of Corrinoid-dependent Methylamine Methyltransferase Reactions in Methanogenic Archaea
    The Journal of biological chemistry, 2008
    Co-Authors: Tsuneo K. Ferguson, Gerhard Gottschalk, Tanja Lienard, Jitesh A. Soares, Joseph A Krzycki
    Abstract:

    Archaeal methane formation from methylamines is initiated by distinct Methyltransferases with specificity for monomethylamine, dimethylamine, or trimethylamine. Each methylamine Methyltransferase methylates a cognate corrinoid protein, which is subsequently demethylated by a second Methyltransferase to form methyl-coenzyme M, the direct methane precursor. Methylation of the corrinoid protein requires reduction of the central cobalt to the highly reducing and nucleophilic Co(I) state. RamA, a 60-kDa monomeric iron-sulfur protein, was isolated from Methanosarcina barkeri and is required for in vitro ATP-dependent reductive activation of methylamine:CoM methyl transfer from all three methylamines. In the absence of the Methyltransferases, highly purified RamA was shown to mediate the ATP-dependent reductive activation of Co(II) corrinoid to the Co(I) state for the monomethylamine corrinoid protein, MtmC. The ramA gene is located near a cluster of genes required for monomethylamine Methyltransferase activity, including MtbA, the methylamine-specific CoM methylase and the pyl operon required for co-translational insertion of pyrrolysine into the active site of methylamine Methyltransferases. RamA possesses a C-terminal ferredoxin-like domain capable of binding two tetranuclear iron-sulfur proteins. Mutliple ramA homologs were identified in genomes of methanogenic Archaea, often encoded near methyltrophic Methyltransferase genes. RamA homologs are also encoded in a diverse selection of bacterial genomes, often located near genes for corrinoid-dependent Methyltransferases. These results suggest that RamA mediates reductive activation of corrinoid proteins and that it is the first functional archetype of COG3894, a family of redox proteins of unknown function.

  • the trimethylamine Methyltransferase gene and multiple dimethylamine Methyltransferase genes of methanosarcina barkeri contain in frame and read through amber codons
    Journal of Bacteriology, 2000
    Co-Authors: Ligi Paul, Donald J Ferguson, Joseph A Krzycki
    Abstract:

    The archaeal 16S rRNA tree has four major branches of methanogens, three of which make methane almost exclusively from carbon dioxide. A family of the fourth branch, the Methanosarcinaceae, is exceptional in that representative species such as Methanosarcina barkeri are also capable of methanogenesis from acetate or methylotrophic substrates, such as methanol, methylated thiols, and methylamines (3, 46). Methylamines are particularly important methane precursors in marine environments, where they arise from the breakdown of common osmolytes (22). Methanogenesis from trimethylamine (TMA) requires the intermediate formation of dimethylamine (DMA) and monomethylamine (MMA), which are subsequently converted to methane (16). The methylation of coenzyme M (CoM) with a methylamine initiates methanogenesis, and as with all substrates, methyl-CoM serves as the direct methane precursor (41, 47). The different pathways of TMA-, DMA-, and MMA-specific CoM methyl transfer can be reconstituted in vitro with only three highly purified polypeptides. A single protein, MtbA, acts as the common CoM methylase for all three methylamines (11). However, different Methyltransferase polypeptides are required to initiate metabolism by demethylation of TMA, DMA, or MMA and subsequent methylation of different corrinoid binding polypeptides. The methylated corrinoid is then demethylated by MtbA to methylate CoM. Each gene or gene product involved in CoM methylation with a methylotrophic substrate is designated according to the following convention. The first two letters, mt, indicate involvement of the gene or gene product in methyl transfer. The third letter indicates the substrate: a for methanol, s for methylthiols, m for MMA, b for DMA, and t for TMA. The final letter designates the polypeptide function, where B is the substrate-specific Methyltransferase that methylates the corrinoid protein with substrate, C is the corrinoid binding polypeptide, and A is the CoM-methylating protein. For MMA:CoM methyl transfer, the specific MMA Methyltransferase is MtmB, which uses MMA to methylate its cognate corrinoid protein, MtmC (5). For DMA:CoM methyl transfer, the specific DMA Methyltransferase is MtbB (44, 45), which methylates the DMA corrinoid protein, MtbC (D. J. Ferguson, N. Gorlatova, L. Paul, D. A. Grahame, and J. A. Krzycki, submitted for publication). The specific TMA Methyltransferase, MttB, copurifies with the TMA corrinoid protein, MttC. MttB has not yet been shown to directly methylate MttC with TMA. However, by analogy with the mechanism of CoM methylation with MMA or methanol, it was proposed that MttB is a TMA Methyltransferase that uses TMA to methylate MttC (10). Figure ​Figure11 illustrates the functions of the gene products methylating CoM with either DMA or TMA. FIG. 1 Schematic of the mtt-mtb1 transcriptional unit. Above the gene sequence are indicated the reactions demonstrated for the gene products, i.e., the DMA and TMA Methyltransferases and their cognate corrinoid proteins. The function of mttP is proposed but ... Methanol:CoM methyl transfer also requires a specific methanol Methyltransferase polypeptide, MtaB, which tightly binds and methylates its cognate corrinoid protein, MtaC (7, 36). Methyl-MtaC is then demethylated by a different CoM methylase, MtaA, which methylates CoM. Methylthiol:CoM methyl transfer has been shown to require only two polypeptides (39, 40). In this case, a third CoM methylase, MtsA, appears to methylate a corrinoid binding protein, MtsB, with methylated thiols like dimethylsulfide (MtsB is the only corrinoid protein which is not named according to the above nomenclature rules). MtsA then demethylates methyl-MtsB and methylates CoM. The genes for MMA- (6), methanol- (35), and methylthiol-dependent (32) CoM methylation have been identified by reverse genetics. These studies have shown that the methylotrophic corrinoid proteins MtaC, MtsB, and MtmC share approximately 50% identity. These methylotrophic corrinoid proteins are also homologous to the cobalamin-binding domain of B12 proteins, such as methionine synthase (28). The methylcobamide-CoM Methyltransferases, MtsA, MtaA, and MtbA, are also 50% similar to one another (14, 26, 32). However, MtaB and MtmB, the methanol and MMA Methyltransferases, have no significant homology with one another. A surprising result from the sequencing of the gene encoding the MMA Methyltransferase, MtmB, was the presence of a single in-frame amber codon midway through the open reading frame that does not function as a stop codon during translation of the mRNA producing the abundant full-length 50-kDa protein (6). The functionally analogous, but nonhomologous, methanol Methyltransferase gene does not contain such an in-frame amber codon. Here, the genes encoding the TMA and DMA Methyltransferases and their cognate corrinoid proteins are characterized for the first time. Interestingly, single in-frame amber codons are found to be a common feature of the genes encoding the polypeptides that initiate methanogenesis from TMA, DMA, or MMA.

  • the trimethylamine Methyltransferase gene and multiple dimethylamine Methyltransferase genes of methanosarcina barkeri contain in frame and read through amber codons
    Journal of Bacteriology, 2000
    Co-Authors: Ligi Paul, Donald J Ferguson, Joseph A Krzycki
    Abstract:

    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.