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Boulias K, Greer EL. Means, mechanisms and consequences of adenine methylation in DNA. Nat Rev Genet 2022; 23:411-428. [PMID: 35256817 PMCID: PMC9354840 DOI: 10.1038/s41576-022-00456-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/31/2022] [Indexed: 12/29/2022]
Abstract
N6-methyl-2'-deoxyadenosine (6mA or m6dA) has been reported in the DNA of prokaryotes and eukaryotes ranging from unicellular protozoa and algae to multicellular plants and mammals. It has been proposed to modulate DNA structure and transcription, transmit information across generations and have a role in disease, among other functions. However, its existence in more recently evolved eukaryotes remains a topic of debate. Recent technological advancements have facilitated the identification and quantification of 6mA even when the modification is exceptionally rare, but each approach has limitations. Critical assessment of existing data, rigorous design of future studies and further development of methods will be required to confirm the presence and biological functions of 6mA in multicellular eukaryotes.
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O’Brown ZK, Greer EL. N6-methyladenine: A Rare and Dynamic DNA Mark. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1389:177-210. [DOI: 10.1007/978-3-031-11454-0_8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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3
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Stenmark B, Harrison OB, Eriksson L, Anton BP, Fomenkov A, Roberts RJ, Tooming-Klunderud A, Bratcher HB, Bray JE, Thulin-Hedberg S, Maiden MCJ, Mölling P. Complete genome and methylome analysis of Neisseria meningitidis associated with increased serogroup Y disease. Sci Rep 2020; 10:3644. [PMID: 32108139 PMCID: PMC7046676 DOI: 10.1038/s41598-020-59509-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Accepted: 01/22/2020] [Indexed: 12/22/2022] Open
Abstract
Invasive meningococcal disease (IMD) due to serogroup Y Neisseria meningitidis emerged in Europe during the 2000s. Draft genomes of serogroup Y isolates in Sweden revealed that although the population structure of these isolates was similar to other serogroup Y isolates internationally, a distinct strain (YI) and more specifically a sublineage (1) of this strain was responsible for the increase of serogroup Y IMD in Sweden. We performed single molecule real-time (SMRT) sequencing on eight serogroup Y isolates from different sublineages to unravel the genetic and epigenetic factors delineating them, in order to understand the serogroup Y emergence. Extensive comparisons between the serogroup Y sublineages of all coding sequences, complex genomic regions, intergenic regions, and methylation motifs revealed small point mutations in genes mainly encoding hypothetical and metabolic proteins, and non-synonymous variants in genes involved in adhesion, iron acquisition, and endotoxin production. The methylation motif CACNNNNNTAC was only found in isolates of sublineage 2. Only seven genes were putatively differentially expressed, and another two genes encoding hypothetical proteins were only present in sublineage 2. These data suggest that the serogroup Y IMD increase in Sweden was most probably due to small changes in genes important for colonization and transmission.
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Affiliation(s)
- Bianca Stenmark
- Department of Laboratory Medicine, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
| | - Odile B Harrison
- Department of Zoology, University of Oxford, Oxford, United Kingdom
| | - Lorraine Eriksson
- Department of Laboratory Medicine, Faculty of Medicine and Health, Örebro University, Örebro, Sweden
| | | | | | | | - Ave Tooming-Klunderud
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, Oslo, Norway
| | - Holly B Bratcher
- Department of Zoology, University of Oxford, Oxford, United Kingdom
| | - James E Bray
- Department of Zoology, University of Oxford, Oxford, United Kingdom
| | - Sara Thulin-Hedberg
- Department of Laboratory Medicine, Faculty of Medicine and Health, Örebro University, Örebro, Sweden
| | | | - Paula Mölling
- Department of Laboratory Medicine, Faculty of Medicine and Health, Örebro University, Örebro, Sweden
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Wang SY, Mao H, Shibuya H, Uzawa S, O’Brown ZK, Wesenberg S, Shin N, Saito TT, Gao J, Meyer BJ, Colaiácovo MP, Greer EL. The demethylase NMAD-1 regulates DNA replication and repair in the Caenorhabditis elegans germline. PLoS Genet 2019; 15:e1008252. [PMID: 31283754 PMCID: PMC6638966 DOI: 10.1371/journal.pgen.1008252] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 07/18/2019] [Accepted: 06/18/2019] [Indexed: 01/03/2023] Open
Abstract
The biological roles of nucleic acid methylation, other than at the C5-position of cytosines in CpG dinucleotides, are still not well understood. Here, we report genetic evidence for a critical role for the putative DNA demethylase NMAD-1 in regulating meiosis in C. elegans. nmad-1 mutants have reduced fertility. They show defects in prophase I of meiosis, which leads to reduced embryo production and an increased incidence of males due to defective chromosomal segregation. In nmad-1 mutant worms, nuclear staging beginning at the leptotene and zygotene stages is disorganized, the cohesin complex is mislocalized at the diplotene and diakinesis stages, and chromosomes are improperly condensed, fused, or lost by the end of diakinesis. RNA sequencing of the nmad-1 germline revealed reduced induction of DNA replication and DNA damage response genes during meiosis, which was coupled with delayed DNA replication, impaired DNA repair and increased apoptosis of maturing oocytes. To begin to understand how NMAD-1 regulates DNA replication and repair, we used immunoprecipitation and mass spectrometry to identify NMAD-1 binding proteins. NMAD-1 binds to multiple proteins that regulate DNA repair and replication, including topoisomerase TOP-2 and co-localizes with TOP-2 on chromatin. Moreover, the majority of TOP-2 binding to chromatin depends on NMAD-1. These results suggest that NMAD-1 functions at DNA replication sites to regulate DNA replication and repair during meiosis. Errors in meiosis are the leading cause of miscarriages, as well as developmental and intellectual disabilities. We have identified that NMAD-1, an enzyme which removes methyl moieties from nucleic acids, is essential for appropriate DNA damage response, DNA replication and meiosis in the nematode C. elegans. We have cytologically and genetically characterized the defects which occur due to deletion of NMAD-1 in the C. elegans germline. Additionally, we have begun to determine molecularly how NMAD-1 can regulate DNA replication, by demonstrating that NMAD-1 binds to components of the DNA replication machinery and is required for their appropriate localization to DNA. Characterizing how epigenetic modifications and the corresponding enzymes that add or remove epigenetic modifications can control the fundamental process of meiosis will have broad implications for understanding and eventually correcting errors in meiosis that disrupt normal development.
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Affiliation(s)
- Simon Yuan Wang
- Division of Newborn Medicine, Children’s Hospital Boston, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston Massachusetts, United States of America
| | - Hui Mao
- Division of Newborn Medicine, Children’s Hospital Boston, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston Massachusetts, United States of America
| | - Hiroki Shibuya
- Division of Newborn Medicine, Children’s Hospital Boston, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston Massachusetts, United States of America
| | - Satoru Uzawa
- Howard Hughes Medical Institute and Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, United States of America
| | - Zach Klapholz O’Brown
- Division of Newborn Medicine, Children’s Hospital Boston, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston Massachusetts, United States of America
| | - Sage Wesenberg
- Division of Newborn Medicine, Children’s Hospital Boston, Boston, Massachusetts, United States of America
| | - Nara Shin
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Takamune T. Saito
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Jinmin Gao
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Barbara J. Meyer
- Howard Hughes Medical Institute and Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, United States of America
| | - Monica P. Colaiácovo
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Eric Lieberman Greer
- Division of Newborn Medicine, Children’s Hospital Boston, Boston, Massachusetts, United States of America
- Department of Pediatrics, Harvard Medical School, Boston Massachusetts, United States of America
- * E-mail:
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Ravoitytė B, Wellinger RE. Non-Canonical Replication Initiation: You're Fired! Genes (Basel) 2017; 8:genes8020054. [PMID: 28134821 PMCID: PMC5333043 DOI: 10.3390/genes8020054] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Accepted: 01/19/2017] [Indexed: 12/25/2022] Open
Abstract
The division of prokaryotic and eukaryotic cells produces two cells that inherit a perfect copy of the genetic material originally derived from the mother cell. The initiation of canonical DNA replication must be coordinated to the cell cycle to ensure the accuracy of genome duplication. Controlled replication initiation depends on a complex interplay of cis-acting DNA sequences, the so-called origins of replication (ori), with trans-acting factors involved in the onset of DNA synthesis. The interplay of cis-acting elements and trans-acting factors ensures that cells initiate replication at sequence-specific sites only once, and in a timely order, to avoid chromosomal endoreplication. However, chromosome breakage and excessive RNA:DNA hybrid formation can cause break-induced (BIR) or transcription-initiated replication (TIR), respectively. These non-canonical replication events are expected to affect eukaryotic genome function and maintenance, and could be important for genome evolution and disease development. In this review, we describe the difference between canonical and non-canonical DNA replication, and focus on mechanistic differences and common features between BIR and TIR. Finally, we discuss open issues on the factors and molecular mechanisms involved in TIR.
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Affiliation(s)
- Bazilė Ravoitytė
- Nature Research Centre, Akademijos g. 2, LT-08412 Vilnius, Lithuania.
| | - Ralf Erik Wellinger
- CABIMER-Universidad de Sevilla, Avd Americo Vespucio sn, 41092 Sevilla, Spain.
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O'Brown ZK, Greer EL. N6-Methyladenine: A Conserved and Dynamic DNA Mark. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 945:213-246. [PMID: 27826841 DOI: 10.1007/978-3-319-43624-1_10] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Chromatin, consisting of deoxyribonucleic acid (DNA) wrapped around histone proteins, facilitates DNA compaction and allows identical DNA codes to confer many different cellular phenotypes. This biological versatility is accomplished in large part by posttranslational modifications to histones and chemical modifications to DNA. These modifications direct the cellular machinery to expand or compact specific chromatin regions and mark regions of the DNA as important for cellular functions. While each of the four bases that make up DNA can be modified (Iyer et al. 2011), this chapter will focus on methylation of the sixth position on adenines (6mA), as this modification has been poorly characterized in recently evolved eukaryotes, but shows promise as a new conserved layer of epigenetic regulation. 6mA was previously thought to be restricted to unicellular organisms, but recent work has revealed its presence in metazoa. Here, we will briefly describe the history of 6mA, examine its evolutionary conservation, and evaluate the current methods for detecting 6mA. We will discuss the enzymes that bind and regulate this mark and finally examine known and potential functions of 6mA in eukaryotes.
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Affiliation(s)
- Zach Klapholz O'Brown
- Division of Newborn Medicine, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA, 02115, USA.,Department of Pediatrics, Harvard Medical School, Boston, MA, 02115, USA
| | - Eric Lieberman Greer
- Division of Newborn Medicine, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA, 02115, USA. .,Department of Pediatrics, Harvard Medical School, Boston, MA, 02115, USA.
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Abstract
The DNA of Escherichia coli contains 19,120 6-methyladenines and 12,045 5-methylcytosines in addition to the four regular bases, and these are formed by the postreplicative action of three DNA methyltransferases. The majority of the methylated bases are formed by the Dam and Dcm methyltransferases encoded by the dam (DNA adenine methyltransferase) and dcm (DNA cytosine methyltransferase) genes. Although not essential, Dam methylation is important for strand discrimination during the repair of replication errors, controlling the frequency of initiation of chromosome replication at oriC, and the regulation of transcription initiation at promoters containing GATC sequences. In contrast, there is no known function for Dcm methylation, although Dcm recognition sites constitute sequence motifs for Very Short Patch repair of T/G base mismatches. In certain bacteria (e.g., Vibrio cholerae, Caulobacter crescentus) adenine methylation is essential, and, in C. crescentus, it is important for temporal gene expression, which, in turn, is required for coordinating chromosome initiation, replication, and division. In practical terms, Dam and Dcm methylation can inhibit restriction enzyme cleavage, decrease transformation frequency in certain bacteria, and decrease the stability of short direct repeats and are necessary for site-directed mutagenesis and to probe eukaryotic structure and function.
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Zautner AE, Goldschmidt AM, Thürmer A, Schuldes J, Bader O, Lugert R, Groß U, Stingl K, Salinas G, Lingner T. SMRT sequencing of the Campylobacter coli BfR-CA-9557 genome sequence reveals unique methylation motifs. BMC Genomics 2015; 16:1088. [PMID: 26689587 PMCID: PMC4687069 DOI: 10.1186/s12864-015-2317-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Accepted: 12/15/2015] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND Campylobacter species are the most prevalent bacterial pathogen causing acute enteritis worldwide. In contrast to Campylobacter jejuni, about 5 % of Campylobacter coli strains exhibit susceptibility to restriction endonuclease digestion by DpnI cutting specifically 5'-G(m)ATC-3' motifs. This indicates significant differences in DNA methylation between both microbial species. The goal of the study was to analyze the methylome of a C. coli strain susceptible to DpnI digestion, to identify its methylation motifs and restriction modification systems (RM-systems), and compare them to related organisms like C. jejuni and Helicobacter pylori. RESULTS Using one SMRT cell and the PacBio RS sequencing technology followed by PacBio Modification and Motif Analysis the complete genome of the DpnI susceptible strain C. coli BfR-CA-9557 was sequenced to 500-fold coverage and assembled into a single contig of 1.7 Mbp. The genome contains a CJIE1-like element prophage and is phylogenetically closer to C. coli clade 1 isolates than clade 3. 45,881 6-methylated adenines (ca. 2.7 % of genome positions) that are predominantly arranged in eight different methylation motifs and 1,788 4-methylated cytosines (ca. 0.1 %) have been detected. Only two of these motifs correspond to known restriction modification motifs. Characteristic for this methylome was the very high fraction of methylation of motifs with mostly above 99 %. CONCLUSIONS Only five dominant methylation motifs have been identified in C. jejuni, which have been associated with known RM-systems. C. coli BFR-CA-9557 shares one (RAATTY) of these, but four ORFs could be assigned to putative Type I RM-systems, seven ORFs to Type II RM-systems and three ORFs to Type IV RM-systems. In accordance with DpnI prescreening RM-system IIP, methylation of GATC motifs was detected in C. coli BfR-CA-9557. A homologous IIP RM-system has been described for H. pylori. The remaining methylation motifs are specific for C. coli BfR-CA-9557 and have been neither detected in C. jejuni nor in H. pylori. The results of this study give us new insights into epigenetics of Campylobacteraceae and provide the groundwork to resolve the function of RM-systems in C. coli.
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Affiliation(s)
- Andreas E Zautner
- Institute for Medical Microbiology, University Medical Center Göttingen, Kreuzbergring 57, D-37075, Göttingen, Germany.
| | - Anne-Marie Goldschmidt
- Institute for Medical Microbiology, University Medical Center Göttingen, Kreuzbergring 57, D-37075, Göttingen, Germany
| | - Andrea Thürmer
- Institute for Microbiology and Genetics, Department of Genomic and Applied Microbiology and Göttingen Genomics Laboratory, Georg-August University Göttingen, Grisebachstr. 8, D-37077, Göttingen, Germany
| | - Jörg Schuldes
- Institute for Microbiology and Genetics, Department of Genomic and Applied Microbiology and Göttingen Genomics Laboratory, Georg-August University Göttingen, Grisebachstr. 8, D-37077, Göttingen, Germany
| | - Oliver Bader
- Institute for Medical Microbiology, University Medical Center Göttingen, Kreuzbergring 57, D-37075, Göttingen, Germany
| | - Raimond Lugert
- Institute for Medical Microbiology, University Medical Center Göttingen, Kreuzbergring 57, D-37075, Göttingen, Germany
| | - Uwe Groß
- Institute for Medical Microbiology, University Medical Center Göttingen, Kreuzbergring 57, D-37075, Göttingen, Germany
| | - Kerstin Stingl
- Federal Institute for Risk Assessment (BfR), Department of Biological Safety - National Reference Laboratory for Campylobacter, D-12277, Berlin, Germany
| | - Gabriela Salinas
- Microarray and Deep-Sequencing Core Facility, University Medical Center Göttingen, Justus-von-Liebig-Weg 11, D-37077, Göttingen, Germany
| | - Thomas Lingner
- Microarray and Deep-Sequencing Core Facility, University Medical Center Göttingen, Justus-von-Liebig-Weg 11, D-37077, Göttingen, Germany
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Molecular Dissection of the Essential Features of the Origin of Replication of the Second Vibrio cholerae Chromosome. mBio 2015. [PMID: 26220967 PMCID: PMC4551981 DOI: 10.1128/mbio.00973-15] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Vibrionaceae family members are interesting models for studying DNA replication initiation, as they contain two circular chromosomes. Chromosome II (chrII) replication is governed by two evolutionarily unique yet highly conserved elements, the origin DNA sequence oriCII and the initiator protein RctB. The minimum functional region of oriCII, oriCII-min, contains multiple elements that are bound by RctB in vitro, but little is known about the specific requirements for individual elements during oriCII initiation. We utilized undirected and site-specific mutagenesis to investigate the functionality of mutant forms of oriCII-min and assessed binding to various mutant forms by RctB. Our analyses showed that deletions, point mutations, and changes in RctB target site spacing or methylation all impaired oriCII-min-based replication. RctB displayed a reduced affinity for most of the low-efficacy origins tested, although its characteristic cooperative binding was generally maintained. Mutations that removed or altered the relative positions of origin components other than RctB binding sites (e.g., AT-rich sequence, DnaA target site) also abolished replicative capacity. Comprehensive mutagenesis and deep-sequencing-based screening (OriSeq) allowed the identification of a previously uncharacterized methylated domain in oriCII that is required for origin function. Together, our results reveal the remarkable evolutionary honing of oriCII and provide new insight into the complex interplay between RctB and oriCII. The genome of the enteric pathogen Vibrio cholerae consists of two chromosomes. While the chromosome I replication origin and its cognate replication initiator protein resemble those of Escherichia coli, the factors responsible for chromosome II replication initiation display no similarity to any other known initiation systems. Here, to enhance our understanding of how this DNA sequence, oriCII, and its initiator protein, RctB, function, we used both targeted mutagenesis and a new random-mutagenesis approach (OriSeq) to finely map the oriCII structural features and sequences required for RctB-mediated DNA replication. Collectively, our findings reveal the extraordinary evolutionary honing of the architecture and motifs that constitute oriCII and reveal a new role for methylation in oriCII-based replication. Finally, our findings suggest that the OriSeq approach is likely to be widely applicable for defining critical bases in cis-acting sequences.
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Abstract
In prokaryotes, alteration in gene expression was observed with the modification of DNA, especially DNA methylation. Such changes are inherited from generation to generation with no alterations in the DNA sequence and represent the epigenetic signal in prokaryotes. DNA methyltransferases are enzymes involved in DNA modification and thus in epigenetic regulation of gene expression. DNA methylation not only affects the thermodynamic stability of DNA, but also changes its curvature. Methylation of specific residues on DNA can affect the protein-DNA interactions. DNA methylation in prokaryotes regulates a number of physiological processes in the bacterial cell including transcription, DNA mismatch repair and replication initiation. Significantly, many reports have suggested a role of DNA methylation in regulating the expression of a number of genes in virulence and pathogenesis thus, making DNA methlytransferases novel targets for the designing of therapeutics. Here, we summarize the current knowledge about the influence of DNA methylation on gene regulation in different bacteria, and on bacterial virulence.
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Affiliation(s)
- Ritesh Kumar
- Department of Biochemistry, Indian Institute of Science, Bangalore, 560012, India,
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López CMR, Lloyd AJ, Leonard K, Wilkinson MJ. Differential effect of three base modifications on DNA thermostability revealed by high resolution melting. Anal Chem 2012; 84:7336-42. [PMID: 22882125 DOI: 10.1021/ac301459x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
High resolution melting (HRM) can detect and quantify the presence of 5-methylcytosine (5mC) in DNA samples, but the ability of HRM to diagnose other DNA modifications remains unexplored. The DNA bases N6-methyladenine and 5-hydroxymethylcytosine occur across almost all phyla. While their function remains controversial, their presence perturbs DNA structure. Such modifications could affect gene regulation, chromatin condensation and DNA packaging. Here, we reveal that DNA containing N6-methyladenine or 5-hydroxymethylcytosine exhibits reduced thermal stability compared to cytosine-methylated DNA. These thermostability changes are sufficiently divergent to allow detection and quantification by HRM analysis. Thus, we report that HRM distinguishes between sequence-identical DNA differing only in the modification type of one base. This approach is also able to distinguish between two DNA fragments carrying both N6-methyladenine and 5-methylcytosine but differing only in the distance separating the modified bases. This finding provides scope for the development of new methods to characterize DNA chemically and to allow for low cost screening of mutant populations of genes involved in base modification. More fundamentally, contrast between the thermostabilizing effects of 5mC on dsDNA compared with the destabilizing effects of N6-methyladenine (m6A) and 5-hydroxymethylcytosine (5hmC) raises the intriguing possibility of an antagonistic relationship between modification types with functional significance.
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Affiliation(s)
- Carlos M Rodríguez López
- Aberystwyth University, IBERS, Institute of Biological, Environmental and Rural Sciences, Aberystwyth, Wales, UK
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Aloui A, Tagourti J, El May A, Joseleau Petit D, Landoulsi A. The effect of methylation on some biological parameters in Salmonella enterica serovar Typhimurium. ACTA ACUST UNITED AC 2011; 59:192-8. [DOI: 10.1016/j.patbio.2009.03.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2008] [Accepted: 03/18/2009] [Indexed: 10/20/2022]
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Replication of Vibrio cholerae chromosome I in Escherichia coli: dependence on dam methylation. J Bacteriol 2010; 192:3903-14. [PMID: 20511501 DOI: 10.1128/jb.00311-10] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We successfully substituted Escherichia coli's origin of replication oriC with the origin region of Vibrio cholerae chromosome I (oriCI(Vc)). Replication from oriCI(Vc) initiated at a similar or slightly reduced cell mass compared to that of normal E. coli oriC. With respect to sequestration-dependent synchrony of initiation and stimulation of initiation by the loss of Hda activity, replication initiation from oriC and oriCI(Vc) were similar. Since Hda is involved in the conversion of DnaA(ATP) (DnaA bound to ATP) to DnaA(ADP) (DnaA bound to ADP), this indicates that DnaA associated with ATP is limiting for V. cholerae chromosome I replication, which similar to what is observed for E. coli. No hda homologue has been identified in V. cholerae yet. In V. cholerae, dam is essential for viability, whereas in E. coli, dam mutants are viable. Replacement of E. coli oriC with oriCI(Vc) allowed us to specifically address the role of the Dam methyltransferase and SeqA in replication initiation from oriCI(Vc). We show that when E. coli's origin of replication is substituted by oriCI(Vc), dam, but not seqA, becomes important for growth, arguing that Dam methylation exerts a critical function at the origin of replication itself. We propose that Dam methylation promotes DnaA-assisted successful duplex opening and replisome assembly at oriCI(Vc) in E. coli. In this model, methylation at oriCI(Vc) would ease DNA melting. This is supported by the fact that the requirement for dam can be alleviated by increasing negative supercoiling of the chromosome through oversupply of the DNA gyrase or loss of SeqA activity.
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14
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Abstract
The DNA of Escherichia coli contains 19,120 6-methyladenines and 12,045 5-methylcytosines in addition to the four regular bases, and these are formed by the postreplicative action of three DNA methyltransferases. The majority of the methylated bases are formed by the Dam and Dcmmethyltransferases encoded by the dam (DNA adenine methyltransferase) and dcm (DNA cytosine methyltransferase) genes. Although not essential, Dam methylation is important for strand discrimination during repair of replication errors, controlling the frequency of initiation of chromosome replication at oriC, and regulation of transcription initiation at promoters containing GATC sequences. In contrast, there is no known function for Dcm methylation, although Dcm recognition sites constitute sequence motifs for Very Short Patch repair of T/G base mismatches. In certain bacteria (e.g., Vibrio cholera and Caulobactercrescentus) adenine methylation is essential, and in C.crescentus it is important for temporal gene expression which, in turn, is required for coordination of chromosome initiation, replication, and division. In practical terms, Dam and Dcm methylation can inhibit restriction enzyme cleavage,decrease transformation frequency in certain bacteria,and decrease the stability of short direct repeats andare necessary for site-directed mutagenesis and to probe eukaryotic structure and function.
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15
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Waldminghaus T, Skarstad K. The Escherichia coli SeqA protein. Plasmid 2009; 61:141-50. [PMID: 19254745 DOI: 10.1016/j.plasmid.2009.02.004] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 02/12/2009] [Accepted: 02/19/2009] [Indexed: 10/21/2022]
Abstract
The Escherichia coli SeqA protein contributes to regulation of chromosome replication by preventing re-initiation at newly replicated origins. SeqA protein binds to new DNA which is hemimethylated at the adenine of GATC sequences. Most of the cellular SeqA is found complexed with the new DNA at the replication forks. In vitro the SeqA protein binds as a dimer to two GATC sites and is capable of forming a helical fiber of dimers through interactions of the N-terminal domain. SeqA can also bind, with less affinity, to fully methylated origins and affect timing of "primary" initiations. In addition to its roles in replication, the SeqA protein may also act in chromosome organization and gene regulation.
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Affiliation(s)
- Torsten Waldminghaus
- Department of Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Rikshospitalet, University of Oslo, 0310 Oslo, Norway
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16
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Marinus MG, Casadesus J. Roles of DNA adenine methylation in host-pathogen interactions: mismatch repair, transcriptional regulation, and more. FEMS Microbiol Rev 2009; 33:488-503. [PMID: 19175412 DOI: 10.1111/j.1574-6976.2008.00159.x] [Citation(s) in RCA: 200] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The DNA adenine methyltransferase (Dam methylase) of Gammaproteobacteria and the cell cycle-regulated methyltransferase (CcrM) methylase of Alphaproteobacteria catalyze an identical reaction (methylation of adenosine moieties using S-adenosyl-methionine as a methyl donor) at similar DNA targets (GATC and GANTC, respectively). Dam and CcrM are of independent evolutionary origin. Each may have evolved from an ancestral restriction-modification system that lost its restriction component, leaving an 'orphan' methylase devoted solely to epigenetic genome modification. The formation of 6-methyladenine reduces the thermodynamic stability of DNA and changes DNA curvature. As a consequence, the methylation state of specific adenosine moieties can affect DNA-protein interactions. Well-known examples include binding of the replication initiation complex to the methylated oriC, recognition of hemimethylated GATCs in newly replicated DNA by the MutHLS mismatch repair complex, and discrimination of methylation states in promoters and regulatory DNA motifs by RNA polymerase and transcription factors. In recent years, Dam and CcrM have been shown to play roles in host-pathogen interactions. These roles are diverse and have only partially been understood. Especially intriguing is the evidence that Dam methylation regulates virulence genes in Escherichia coli, Salmonella, and Yersinia at the posttranscriptional level.
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Affiliation(s)
- Martin G Marinus
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts, Worcester, USA
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17
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Abstract
Escherichia coli is a model system to study the mechanism of DNA replication and its regulation during the cell cycle. One regulatory pathway ensures that initiation of DNA replication from the chromosomal origin, oriC, is synchronous and occurs at the proper time in the bacterial cell cycle. A major player in this pathway is SeqA protein and involves its ability to bind preferentially to oriC when it is hemi-methylated. The second pathway modulates DnaA activity by stimulating the hydrolysis of ATP bound to DnaA protein. The regulatory inactivation of DnaA function involves an interaction with Hda protein and the beta dimer, which functions as a sliding clamp for the replicase, DNA polymerase III holoenzyme. The datA locus represents a third mechanism, which appears to influence the availability of DnaA protein in supporting rifampicin-resistant initiations.
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Affiliation(s)
- Jon M Kaguni
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319, USA.
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18
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Benham CJ, Bi C. The analysis of stress-induced duplex destabilization in long genomic DNA sequences. J Comput Biol 2005; 11:519-43. [PMID: 15579230 DOI: 10.1089/cmb.2004.11.519] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We present a method for calculating predicted locations and extents of stress-induced DNA duplex destabilization (SIDD) as functions of base sequence and stress level in long DNA molecules. The base pair denaturation energies are assigned individually, so the influences of near neighbors, methylated bases, adducts, or lesions can be included. Sample calculations indicate that copolymeric energetics give results that are close to those derived when full near-neighbor energetics are used; small but potentially informative differences occur only in the calculated SIDD properties of moderately destabilized regions. The method presented here for analyzing long sequences calculates the destabilization properties within windows of fixed length N, with successive windows displaced by an offset distance d(o). The final values of the relevant destabilization parameters for each base pair are calculated as weighted averages of the values computed for each window in which that base pair appears. This approach implicitly assumes that the strength of the direct coupling between remote base pairs that is induced by the imposed stress attenuates with their separation distance. This strategy enables calculations of the destabilization properties of DNA sequences of any length, up to and including complete chromosomes. We illustrate its utility by calculating the destabilization properties of the entire E. coli genomic DNA sequence. A preliminary analysis of the results shows that promoters are associated with SIDD regions in a highly statistically significant manner, suggesting that SIDD attributes may prove useful in the computational prediction of promoter locations in prokaryotes.
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Affiliation(s)
- Craig J Benham
- UC Davis Genome Center, University of California, One Shields Avenue, Davis, CA 95616, USA.
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19
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Saha A, Haralalka S, Bhadra RK. A naturally occurring point mutation in the 13-mer R repeat affects the oriC function of the large chromosome of Vibrio cholerae O1 classical biotype. Arch Microbiol 2004; 182:421-7. [PMID: 15375645 DOI: 10.1007/s00203-004-0708-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The genome of Vibrio cholerae consists of two circular chromosomes of different sizes. Here, a comparative analysis of the replication origins of the large chromosomes (oriCIvc) of classical and El Torbio types of the pathogen is reported. Extensive nucleotide sequence analyses revealed that the oriCIvc region has six DnaA boxes instead of the five found in Escherichia coli oriC. The additional DnaA box, designated Rv, was unique in V. cholerae as well as in other members of the family Vibrionaceae. However, Rv was not found to be essential for the autonomous replication function of the 307-bp oriCIvc minimal region. In contrast to El Tor and the recently evolved V. cholerae 0139 strains, the oriCIvc region of the classical biotype showed only a single base transition (T-->G) in a highly conserved AT-rich 13-mer R repeat region. From the minichromosome copy number and its transformational efficiency analyses, it appears that the single base substitution in the oriCIvc of the classical biotype has a significant effect on its replication initiation.
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Affiliation(s)
- Arjun Saha
- Infectious Diseases Division, Indian Institute of Chemical Biology, Kolkata, India
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20
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Rein T, Kobayashi T, Malott M, Leffak M, DePamphilis ML. DNA methylation at mammalian replication origins. J Biol Chem 1999; 274:25792-800. [PMID: 10464318 DOI: 10.1074/jbc.274.36.25792] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In Escherichia coli, DNA methylation regulates both origin usage and the time required to reassemble prereplication complexes at replication origins. In mammals, at least three replication origins are associated with a high density cluster of methylated CpG dinucleotides, and others whose methylation status has not yet been characterized have the potential to exhibit a similar DNA methylation pattern. One of these origins is found within the approximately 2-kilobase pair region upstream of the human c-myc gene that contains 86 CpGs. Application of the bisulfite method for detecting 5-methylcytosines at specific DNA sequences revealed that this region was not methylated in either total genomic DNA or newly synthesized DNA. Therefore, DNA methylation is not a universal component of mammalian replication origins. To determine whether or not DNA methylation plays a role in regulating the activity of origins that are methylated, the rate of remethylation and the effect of hypomethylation were determined at origin beta (ori-beta), downstream of the hamster DHFR gene. Remethylation at ori-beta did not begin until approximately 500 base pairs of DNA was synthesized, but it was then completed by the time that 4 kilobase pairs of DNA was synthesized (<3 min after release into S phase). Thus, DNA methylation cannot play a significant role in regulating reassembly of prereplication complexes in mammalian cells, as it does in E. coli. To determine whether or not DNA methylation plays any role in origin activity, hypomethylated hamster cells were examined for ori-beta activity. Cells that were >50% reduced in methylation at ori-beta no longer selectively activated ori-beta. Therefore, at some loci, DNA methylation either directly or indirectly determines where replication begins.
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Affiliation(s)
- T Rein
- NICHD, National Institutes of Health, Bethesda, Maryland 20892-2753, USA
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21
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Polaczek P, Kwan K, Campbell JL. Unwinding of the Escherichia coli origin of replication (oriC) can occur in the absence of initiation proteins but is stabilized by DnaA and histone-like proteins IHF or HU. Plasmid 1998; 39:77-83. [PMID: 9473448 DOI: 10.1006/plas.1997.1328] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The unwinding of the origin of replication (oriC) is a critical step in initiation of DNA replication in Escherichia coli. Previous observations indicate that efficient unwinding of supercoiled plasmid templates containing oriC sequences requires the DnaA initiation protein and one or more accessory factors. The precise contribution of each protein to this process is unknown. Here, we demonstrate that unwinding can occur under physiological conditions at the same bases in oriC, in either the presence or the absence of initiation proteins, as detected by a single-strand specific nuclease, P1. This suggests that oriC unwinding is a spontaneous event determined solely by DNA sequence. DnaA and IHF, as part of a large nucleoprotein complex, may function to stabilize the DNA strand opening prior to initiation of DNA replication.
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Affiliation(s)
- P Polaczek
- Braun Laboratories 147-75, California Institute of Technology, Pasadena 91125, USA
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22
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Chattoraj DK, Schneider TD. Replication control of plasmid P1 and its host chromosome: the common ground. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1997; 57:145-86. [PMID: 9175433 DOI: 10.1016/s0079-6603(08)60280-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- D K Chattoraj
- Laboratory of Biochemistry NCI, NIH Bethesda, Maryland 20892, USA
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23
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Rein T, Zorbas H, DePamphilis ML. Active mammalian replication origins are associated with a high-density cluster of mCpG dinucleotides. Mol Cell Biol 1997; 17:416-26. [PMID: 8972222 PMCID: PMC231766 DOI: 10.1128/mcb.17.1.416] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
ori-beta is a well-characterized origin of bidirectional replication (OBR) located approximately 17 kb downstream of the dihydrofolate reductase gene in hamster cell chromosomes. The approximately 2-kb region of ori-beta that exhibits greatest replication initiation activity also contains 12 potential methylation sites in the form of CpG dinucleotides. To ascertain whether DNA methylation might play a role at mammalian replication origins, the methylation status of these sites was examined with bisulfite to chemically distinguish cytosine (C) from 5-methylcytosine (mC). All of the CpGs were methylated, and nine of them were located within 356 bp flanking the minimal OBR, creating a high-density cluster of mCpGs that was approximately 10 times greater than average for human DNA. However, the previously reported densely methylated island in which all cytosines were methylated regardless of their dinucleotide composition was not detected and appeared to be an experimental artifact. A second OBR, located at the 5' end of the RPS14 gene, exhibited a strikingly similar methylation pattern, and the organization of CpG dinucleotides at other mammalian origins revealed the potential for high-density CpG methylation. Moreover, analysis of bromodeoxyuridine-labeled nascent DNA confirmed that active replication origins were methylated. These results suggest that a high-density cluster of mCpG dinucleotides may play a role in either the establishment or the regulation of mammalian replication origins.
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Affiliation(s)
- T Rein
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-2753, USA.
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24
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Abeles A, Brendler T, Austin S. Evidence of two levels of control of P1 oriR and host oriC replication origins by DNA adenine methylation. J Bacteriol 1993; 175:7801-7. [PMID: 8253669 PMCID: PMC206955 DOI: 10.1128/jb.175.24.7801-7807.1993] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
A mutant mini-P1 plasmid with increased copy number can be established in Dam- strains of Escherichia coli, where mini-P1 plasmid replication is normally blocked. Comparison of this plasmid and a plasmid driven by the host oriC replication origin showed that both origins are subject to control by methylation at two different levels. First, both origins appear to be subject to negative regulation acting at the level of hemimethylation. This probably involves the sequestration of the hemimethylated DNA produced by replication, as has been previously described for oriC. Second, both origins show a positive requirement for adenine methylation for efficient function in vivo. This conclusion is supported by the behavior of the P1 origin in an improved in vitro replication system. In vitro, where sequestration of hemimethylated DNA is not expected to occur, the hemimethylated P1 origin DNA was fully functional as a template. However, the activity of fully unmethylated DNA was severely restricted in comparison with that of either of the methylated forms. This in vitro uncoupling of the two effects of origin methylation suggests that two separate mechanisms are involved.
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Affiliation(s)
- A Abeles
- Laboratory of Chromosome Biology, National Cancer Institute-Frederick Cancer Research and Development Center, Maryland 21701-1201
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25
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26
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Murchie AI, Bowater R, Aboul-ela F, Lilley DM. Helix opening transitions in supercoiled DNA. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1131:1-15. [PMID: 1581350 DOI: 10.1016/0167-4781(92)90091-d] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- A I Murchie
- Department of Biochemistry, University, Dundee, UK
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27
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Abstract
Unmethylated, fully methylated, and hemimethylated oriC-containing plasmids were assayed as substrates for DNA replication in vitro by using a system reconstituted with pure proteins. In contrast to the in vivo situation, all three substrates were initiated efficiently; the fully methylated plasmid was about twice as active as the other two.
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Affiliation(s)
- E Boye
- Department of Biophysics, Norwegian Radium Hospital, Oslo
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28
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Abstract
The core of the P1 plasmid replication origin consists of a series of 7-bp repeats and a G+C-rich stretch. Methylation of the GATC sequences in the repeats is essential. Forty different single-base mutations in the region were isolated and assayed for origin function. A single-base change within any 7-bp repeat could block the origin, irrespective of whether GATC bases were affected. The repeats themselves were critical, but the short intervals between them were not. Mutations in the G+C-rich region showed it to be a spacer whose exact length is important but whose sequence can vary considerably. It maintains a precise distance between the 7-bp repeats and binding sites for the P1 RepA initiator protein. It may also serve as a clamp to limit strand separation during initiation.
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Affiliation(s)
- T Brendler
- Laboratory of Chromosome Biology, NCI-Frederick Cancer Research and Development Center, Maryland 21702
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29
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Abstract
Deletion analysis has shown that the segment at the IS50 inside (I) end that is needed for efficient transposition is approximately 19 bp long. Dam methylation at two 5' GATC sequences within this segment decreases I-end transposition activity. A third 5' GATC sequence is present at bp 21-24 of the I end. The comparisons presented here show that extension of the I end from 19 to 24 bp decreases its transposition activity in dam cells 5- to 50-fold, depending on the overall transposon structure.
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Affiliation(s)
- K W Dodson
- Washington University Medical School, Department of Molecular Microbiology, St. Louis, Missouri 63110-1093
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30
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Gammie AE, Crosa JH. Roles of DNA adenine methylation in controlling replication of the REPI replicon of plasmid pColV-K30. Mol Microbiol 1991; 5:495-503. [PMID: 2041481 DOI: 10.1111/j.1365-2958.1991.tb02133.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
DNA adenine methylation controls DNA replication of plasmids containing the prototypic REPI replicon by affecting protein recognition and by altering the helical stability of the origin. Denaturing gradient gel electrophoresis shows that adenine methylated origin DNA is more easily melted than unmethylated. However, because an added DNA adenine methylation (dam) site at the origin, whether in or out of phase with other helically aligned dam sites, actually prevents replication, we conclude that destabilization of the helix is not the exclusive function of adenine methylation in REPI replication. We find that the conformation and degree of methylation at the origin, features which are important for protein recognition, are essential for replication. In fact, RepI, a protein required for replication initiation at REPI replicons, contains a region homologous with a domain in proteins which specifically recognize and bind 5'-GATC-3'. We propose that the dam sites in the origin play a dual role: one is destabilization of the helix, and the other is protein recognition.
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Affiliation(s)
- A E Gammie
- Department of Microbiology and Immunology, Oregon Health Sciences University, Portland 97201
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31
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Maeda Y, Nunomura K, Ohtsubo E. Differential scanning calorimetric study of the effect of intercalators and other kinds of DNA-binding drugs on the stepwise melting of plasmid DNA. J Mol Biol 1990; 215:321-9. [PMID: 1698988 DOI: 10.1016/s0022-2836(05)80350-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The effect of intercalating drugs (the anthracycline group of antibiotics, ethidium bromide, actinomycin D) on stepwise melting of DNA was studied by differential scanning calorimetry (DSC). The DSC DNA melting profile of plasmid pJL3-TB5 DNA (5277 base-pairs in length) consists of seven peaks, and all the intercalators caused shifting of these peaks, particularly those formed at the high temperature ranges, to the higher temperature ranges in a characteristic manner depending upon the binding strength of the drug. The analysis of the anthracycline group of antibiotics, such as aclacinomycin A, daunomycin, adriamycin and pyrarubicin, indicates that the difference in binding is due to the sugar moiety at position O-7 of the chromophore in these antibiotics. Analysis on the basis of the helix-coil transition theory suggests that the anthracycline group of antibiotics interact preferentially with the 5'-CG-3' sequences. The effect of various DNA-binding drugs other than intercalators on stepwise melting of DNA was then studied by DSC. The representative drugs examined were distamycin A, peplomycin, cis-dichlorodiamine-platinum(II) (cis-DDP or cis-Platin) and mitomycin C, which differ in their mode of interaction with DNA; namely, minor groove binding, strand cleavage and intrastrand or interstrand cross-linking. Distamycin A caused shifting of the DSC peaks at the low temperature ranges to a higher temperature range, whereas peplomycin and cis-DDP caused shifting of all the DSC peaks to form a broad peak at a lower temperature range, suggesting that the DSC DNA melting profiles are affected in a characteristic manner depending upon the interaction mode of the drug.
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Affiliation(s)
- Y Maeda
- Institute of Applied Microbiology, University of Tokyo, Japan
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32
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Campbell JL, Kleckner N. E. coli oriC and the dnaA gene promoter are sequestered from dam methyltransferase following the passage of the chromosomal replication fork. Cell 1990; 62:967-79. [PMID: 1697508 DOI: 10.1016/0092-8674(90)90271-f] [Citation(s) in RCA: 353] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have examined individual GATC sites throughout the E. coli genome for their kinetics of remethylation by dam methyltransferase following the passage of the chromosomal replication fork. We present evidence for three major conclusions: that oriC is a single function unit that is specifically sequestered from dam methyltransferase for a significant period of time and then released; that the dnaA promoter region is subject to sequestration analogous to that observed at oriC and thus that hemimethylation-dependent sequestration is a general phenomenon; and that each round of replication initiation triggers a transient, temporally coordinate block in both reinitiation at oriC and expression of the dnaA gene. These and other observations are all consistent with the notion that hemimethylation in these two regions acts coordinately to ensure that every origin undergoes initiation once and only once per cell cycle; other possible roles for sequestration at dnaA are also considered.
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Affiliation(s)
- J L Campbell
- Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, Massachusetts 02138
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33
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Abstract
Replication of plasmid deoxyribonucleic acid (DNA) is dependent on three stages: initiation, elongation, and termination. The first stage, initiation, depends on plasmid-encoded properties such as the replication origin and, in most cases, the replication initiation protein (Rep protein). In recent years the understanding of initiation and regulation of plasmid replication in Escherichia coli has increased considerably, but it is only for the ColE1-type plasmids that significant biochemical data about the initial priming reaction of DNA synthesis exist. Detailed models have been developed for the initiation and regulation of ColE1 replication. For other plasmids, such as pSC101, some hypotheses for priming mechanisms and replication initiation are presented. These hypotheses are based on experimental evidence and speculative comparisons with other systems, e.g., the chromosomal origin of E. coli. In most cases, knowledge concerning plasmid replication is limited to regulation mechanisms. These mechanisms coordinate plasmid replication to the host cell cycle, and they also seem to determine the host range of a plasmid. Most plasmids studied exhibit a narrow host range, limited to E. coli and related bacteria. In contrast, some others, such as the IncP plasmid RK2 and the IncQ plasmid RSF1010, are able to replicate in nearly all gram-negative bacteria. This broad host range may depend on the correct expression of the essential rep genes, which may be mediated by a complex regulatory mechanism (RK2) or by the use of different promoters (RSF1010). Alternatively or additionally, owing to the structure of their origin and/or to different forms of their replication initiation proteins, broad-host-range plasmids may adapt better to the host enzymes that participate in initiation. Furthermore, a broad host range can result when replication initiation is independent of host proteins, as is found in the priming reaction of RSF1010.
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34
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Abstract
In Escherichia coli the methylation of the adenine in the sequence 5'-GATC-3' is catalysed by the dam gene product, a DNA adenine methylase. We review the proposed roles for this methylation, and the sequence it modifies, in mismatch repair, DNA-protein interaction, gene expression, the initiation of chromosome replication, chromosome segregation, chromosome structure and the occurrence of mutational hotspots.
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35
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Affiliation(s)
- M Masters
- Department of Molecular Biology, University of Edinburgh, UK
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36
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Murchie AI, Lilley DM. Base methylation and local DNA helix stability. Effect on the kinetics of cruciform extrusion. J Mol Biol 1989; 205:593-602. [PMID: 2648008 DOI: 10.1016/0022-2836(89)90228-3] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We have studied the effect of base methylation on the rate of cruciform extrusion. A number of inverted repeats with central restriction sites were methylated at N6-adenine and C-5-cytosine, and rate constants for cruciform extrusion at 37 degrees C were measured. The effect of A-methylation at two bases was to enhance the rate for extrusion by nearly fourfold, while C-methylation lead to reduced extrusion rates, by factors of 1.7 and 2.7. The bkb inverted repeat, which has a central GGATCC sequence, was independently and simultaneously methylated at adenine and cytosine. It was found that the effects of the two kinds of modification could be treated effectively independently. The results reveal the local helical destabilization and stabilization due to A and C-methylation, respectively.
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Affiliation(s)
- A I Murchie
- Department of Biochemistry, The University, Dundee, U.K
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37
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Abstract
An activity that unwinds double-stranded RNA has been reported to exist in several organisms. We have analyzed the RNA intermediates and final products of the unwinding reaction. Although the RNA becomes sensitive to single strand-specific ribonucleases during the reaction, the duplex is never completely unwound. Furthermore, the base pairing properties of the RNA are permanently altered; the reacted RNA cannot rehybridize to form the original duplex. We demonstrate that during the reaction many, but not all, of the adenosine residues are converted to inosine residues, and we propose that the covalent modification is responsible for the irreversible change in base pairing properties. Possible biological roles for the unwinding/modifying activity, as well as its relevance to antisense RNA experiments, are discussed.
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Affiliation(s)
- B L Bass
- Hutchinson Cancer Research Center, Seattle, Washington 98104
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38
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Maeda Y, Takahashi K, Yamaki H, Ohtsubo E. Helix-coil transition of plasmid DNA by adiabatic differential scanning microcalorimetry. Biopolymers 1988; 27:1917-25. [PMID: 3240359 DOI: 10.1002/bip.360271206] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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