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Went SC, Picton DM, Morgan RD, Nelson A, Brady A, Mariano G, Dryden DTF, Smith DL, Wenner N, Hinton JCD, Blower TR. Structure and rational engineering of the PglX methyltransferase and specificity factor for BREX phage defence. Nat Commun 2024; 15:7236. [PMID: 39174540 PMCID: PMC11341690 DOI: 10.1038/s41467-024-51629-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Accepted: 08/12/2024] [Indexed: 08/24/2024] Open
Abstract
Bacteria have evolved a broad range of systems that provide defence against their viral predators, bacteriophages. Bacteriophage Exclusion (BREX) systems recognise and methylate 6 bp non-palindromic motifs within the host genome, and prevent replication of non-methylated phage DNA that encodes these same motifs. How BREX recognises cognate motifs has not been fully understood. In this study we characterise BREX from pathogenic Salmonella and present X-ray crystallographic structures of the conserved BREX protein, PglX. The PglX N-terminal domain encodes the methyltransferase, whereas the C-terminal domain is for motif recognition. We also present the structure of PglX bound to the phage-derived DNA mimic, Ocr, an inhibitor of BREX activity. Our analyses propose modes for DNA-binding by PglX and indicate that both methyltransferase activity and defence require larger BREX complexes. Through rational engineering of PglX we broaden both the range of phages targeted, and the host motif sequences that are methylated by BREX. Our data demonstrate that PglX is used to recognise specific DNA sequences for BREX activity, contributing to motif recognition for both phage defence and host methylation.
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Affiliation(s)
- Sam C Went
- Department of Biosciences, Durham University, South Road, Durham, UK
| | - David M Picton
- Department of Biosciences, Durham University, South Road, Durham, UK
| | | | - Andrew Nelson
- Faculty of Health and Life Sciences, Northumbria University, Newcastle Upon Tyne, UK
| | - Aisling Brady
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK
| | - Giuseppina Mariano
- Department of Microbial Sciences, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
| | - David T F Dryden
- Department of Biosciences, Durham University, South Road, Durham, UK
| | - Darren L Smith
- Faculty of Health and Life Sciences, Northumbria University, Newcastle Upon Tyne, UK
| | - Nicolas Wenner
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK
| | - Jay C D Hinton
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK
| | - Tim R Blower
- Department of Biosciences, Durham University, South Road, Durham, UK.
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2
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Skutel M, Yanovskaya D, Demkina A, Shenfeld A, Musharova O, Severinov K, Isaev A. RecA-dependent or independent recombination of plasmid DNA generates a conflict with the host EcoKI immunity by launching restriction alleviation. Nucleic Acids Res 2024; 52:5195-5208. [PMID: 38567730 PMCID: PMC11109961 DOI: 10.1093/nar/gkae243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 03/17/2024] [Accepted: 03/22/2024] [Indexed: 05/23/2024] Open
Abstract
Bacterial defence systems are tightly regulated to avoid autoimmunity. In Type I restriction-modification (R-M) systems, a specific mechanism called restriction alleviation (RA) controls the activity of the restriction module. In the case of the Escherichia coli Type I R-M system EcoKI, RA proceeds through ClpXP-mediated proteolysis of restriction complexes bound to non-methylated sites that appear after replication or reparation of host DNA. Here, we show that RA is also induced in the presence of plasmids carrying EcoKI recognition sites, a phenomenon we refer to as plasmid-induced RA. Further, we show that the anti-restriction behavior of plasmid-borne non-conjugative transposons such as Tn5053, previously attributed to their ardD loci, is due to plasmid-induced RA. Plasmids carrying both EcoKI and Chi sites induce RA in RecA- and RecBCD-dependent manner. However, inactivation of both RecA and RecBCD restores RA, indicating that there exists an alternative, RecA-independent, homologous recombination pathway that is blocked in the presence of RecBCD. Indeed, plasmid-induced RA in a RecBCD-deficient background does not depend on the presence of Chi sites. We propose that processing of random dsDNA breaks in plasmid DNA via homologous recombination generates non-methylated EcoKI sites, which attract EcoKI restriction complexes channeling them for ClpXP-mediated proteolysis.
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Affiliation(s)
- Mikhail Skutel
- Skolkovo Institute of Science and Technology, Moscow, Russia
| | - Daria Yanovskaya
- Skolkovo Institute of Science and Technology, Moscow, Russia
- Moscow Institute of Physics and Technology, Moscow, Russia
| | - Alina Demkina
- Skolkovo Institute of Science and Technology, Moscow, Russia
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia
| | | | - Olga Musharova
- Skolkovo Institute of Science and Technology, Moscow, Russia
- Institute of Molecular Genetics, National Research Center Kurchatov Institute, Moscow, Russia
| | - Konstantin Severinov
- Waksman Institute of Microbiology, Piscataway, USA
- Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Artem Isaev
- Skolkovo Institute of Science and Technology, Moscow, Russia
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3
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Weigele P, Raleigh EA. Biosynthesis and Function of Modified Bases in Bacteria and Their Viruses. Chem Rev 2016; 116:12655-12687. [PMID: 27319741 DOI: 10.1021/acs.chemrev.6b00114] [Citation(s) in RCA: 120] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Naturally occurring modification of the canonical A, G, C, and T bases can be found in the DNA of cellular organisms and viruses from all domains of life. Bacterial viruses (bacteriophages) are a particularly rich but still underexploited source of such modified variant nucleotides. The modifications conserve the coding and base-pairing functions of DNA, but add regulatory and protective functions. In prokaryotes, modified bases appear primarily to be part of an arms race between bacteriophages (and other genomic parasites) and their hosts, although, as in eukaryotes, some modifications have been adapted to convey epigenetic information. The first half of this review catalogs the identification and diversity of DNA modifications found in bacteria and bacteriophages. What is known about the biogenesis, context, and function of these modifications are also described. The second part of the review places these DNA modifications in the context of the arms race between bacteria and bacteriophages. It focuses particularly on the defense and counter-defense strategies that turn on direct recognition of the presence of a modified base. Where modification has been shown to affect other DNA transactions, such as expression and chromosome segregation, that is summarized, with reference to recent reviews.
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Affiliation(s)
- Peter Weigele
- Chemical Biology, New England Biolabs , Ipswich, Massachusetts 01938, United States
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4
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Pleška M, Qian L, Okura R, Bergmiller T, Wakamoto Y, Kussell E, Guet C. Bacterial Autoimmunity Due to a Restriction-Modification System. Curr Biol 2016; 26:404-9. [DOI: 10.1016/j.cub.2015.12.041] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Revised: 11/08/2015] [Accepted: 12/10/2015] [Indexed: 01/25/2023]
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5
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Simons M, Diffin FM, Szczelkun MD. ClpXP protease targets long-lived DNA translocation states of a helicase-like motor to cause restriction alleviation. Nucleic Acids Res 2014; 42:12082-91. [PMID: 25260590 PMCID: PMC4231737 DOI: 10.1093/nar/gku851] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
We investigated how Escherichia coli ClpXP targets the helicase-nuclease (HsdR) subunit of the bacterial Type I restriction–modification enzyme EcoKI during restriction alleviation (RA). RA is a temporary reduction in endonuclease activity that occurs when Type I enzymes bind unmodified recognition sites on the host genome. These conditions arise upon acquisition of a new system by a naïve host, upon generation of new sites by genome rearrangement/mutation or during homologous recombination between hemimethylated DNA. Using recombinant DNA and proteins in vitro, we demonstrate that ClpXP targets EcoKI HsdR during dsDNA translocation on circular DNA but not on linear DNA. Protein roadblocks did not activate HsdR proteolysis. We suggest that DNA translocation lifetime, which is elevated on circular DNA relative to linear DNA, is important to RA. To identify the ClpX degradation tag (degron) in HsdR, we used bioinformatics and biochemical assays to design N- and C-terminal mutations that were analysed in vitro and in vivo. None of the mutants produced a phenotype consistent with loss of the degron, suggesting an as-yet-unidentified recognition pathway. We note that an EcoKI nuclease mutant still produces cell death in a clpx− strain, consistent with DNA damage induced by unregulated motor activity.
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Affiliation(s)
- Michelle Simons
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Fiona M Diffin
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Mark D Szczelkun
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
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6
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Loenen WAM, Dryden DTF, Raleigh EA, Wilson GG. Type I restriction enzymes and their relatives. Nucleic Acids Res 2014; 42:20-44. [PMID: 24068554 PMCID: PMC3874165 DOI: 10.1093/nar/gkt847] [Citation(s) in RCA: 175] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 08/26/2013] [Accepted: 08/29/2013] [Indexed: 12/24/2022] Open
Abstract
Type I restriction enzymes (REases) are large pentameric proteins with separate restriction (R), methylation (M) and DNA sequence-recognition (S) subunits. They were the first REases to be discovered and purified, but unlike the enormously useful Type II REases, they have yet to find a place in the enzymatic toolbox of molecular biologists. Type I enzymes have been difficult to characterize, but this is changing as genome analysis reveals their genes, and methylome analysis reveals their recognition sequences. Several Type I REases have been studied in detail and what has been learned about them invites greater attention. In this article, we discuss aspects of the biochemistry, biology and regulation of Type I REases, and of the mechanisms that bacteriophages and plasmids have evolved to evade them. Type I REases have a remarkable ability to change sequence specificity by domain shuffling and rearrangements. We summarize the classic experiments and observations that led to this discovery, and we discuss how this ability depends on the modular organizations of the enzymes and of their S subunits. Finally, we describe examples of Type II restriction-modification systems that have features in common with Type I enzymes, with emphasis on the varied Type IIG enzymes.
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Affiliation(s)
- Wil A. M. Loenen
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
| | - David T. F. Dryden
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
| | - Elisabeth A. Raleigh
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
| | - Geoffrey G. Wilson
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
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7
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Klaiman D, Steinfels-Kohn E, Kaufmann G. A DNA break inducer activates the anticodon nuclease RloC and the adaptive immunity in Acinetobacter baylyi ADP1. Nucleic Acids Res 2013; 42:328-39. [PMID: 24062157 PMCID: PMC3874168 DOI: 10.1093/nar/gkt851] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Double-stranded DNA breaks (DSB) cause bacteria to augment expression of DNA repair and various stress response proteins. A puzzling exception educes the anticodon nuclease (ACNase) RloC, which resembles the DSB responder Rad50 and the antiviral, translation-disabling ACNase PrrC. While PrrC's ACNase is regulated by a DNA restriction-modification (R-M) protein and a phage anti-DNA restriction peptide, RloC has an internal ACNase switch comprising a putative DSB sensor and coupled ATPase. Further exploration of RloC's controls revealed, first, that its ACNase is stabilized by the activating DNA and hydrolysed nucleotide. Second, DSB inducers activated RloC's ACNase in heterologous contexts as well as in a natural host, even when R-M deficient. Third, the DSB-induced activation of the indigenous RloC led to partial and temporary disruption of tRNA(Glu) and tRNA(Gln). Lastly, accumulation of CRISPR-derived RNA that occurred in parallel raises the possibility that the adaptive immunity and RloC provide the genotoxicated host with complementary protection from impending infections.
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Affiliation(s)
- Daniel Klaiman
- Department of Biochemistry and Molecular Biology, Tel Aviv University, Tel Aviv 69978, Israel
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8
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Abstract
The 1952 observation of host-induced non-hereditary variation in bacteriophages by Salvador Luria and Mary Human led to the discovery in the 1960s of modifying enzymes that glucosylate hydroxymethylcytosine in T-even phages and of genes encoding corresponding host activities that restrict non-glucosylated phage DNA: rglA and rglB (restricts glucoseless phage). In the 1980’s, appreciation of the biological scope of these activities was dramatically expanded with the demonstration that plant and animal DNA was also sensitive to restriction in cloning experiments. The rgl genes were renamed mcrA and mcrBC (modified cytosine restriction). The new class of modification-dependent restriction enzymes was named Type IV, as distinct from the familiar modification-blocked Types I–III. A third Escherichia coli enzyme, mrr (modified DNA rejection and restriction) recognizes both methylcytosine and methyladenine. In recent years, the universe of modification-dependent enzymes has expanded greatly. Technical advances allow use of Type IV enzymes to study epigenetic mechanisms in mammals and plants. Type IV enzymes recognize modified DNA with low sequence selectivity and have emerged many times independently during evolution. Here, we review biochemical and structural data on these proteins, the resurgent interest in Type IV enzymes as tools for epigenetic research and the evolutionary pressures on these systems.
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Affiliation(s)
- Wil A M Loenen
- Leiden University Medical Center, P.O. Box 9600 2300RC Leiden, The Netherlands and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
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9
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Smith RM, Jacklin AJ, Marshall JJT, Sobott F, Halford SE. Organization of the BcgI restriction-modification protein for the transfer of one methyl group to DNA. Nucleic Acids Res 2012; 41:405-17. [PMID: 23147004 PMCID: PMC3592466 DOI: 10.1093/nar/gks1000] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The Type IIB restriction–modification protein BcgI contains A and B subunits in a
2:1 ratio: A has the active sites for both endonuclease and methyltransferase functions
while B recognizes the DNA. Like almost all Type IIB systems, BcgI needs two unmethylated
sites for nuclease activity; it cuts both sites upstream and downstream of the recognition
sequence, hydrolyzing eight phosphodiester bonds in a single synaptic complex. This
complex may incorporate four A2B protomers to give the eight catalytic centres
(one per A subunit) needed to cut all eight bonds. The BcgI recognition sequence contains
one adenine in each strand that can be N6-methylated. Although most DNA
methyltransferases operate at both unmethylated and hemi-methylated sites, BcgI
methyltransferase is only effective at hemi-methylated sites, where the nuclease component
is inactive. Unlike the nuclease, the methyltransferase acts at solitary sites,
functioning catalytically rather than stoichiometrically. Though it transfers one methyl
group at a time, presumably through a single A subunit, BcgI methyltransferase can be
activated by adding extra A subunits, either individually or as part of A2B
protomers, which indicates that it requires an assembly containing at least two
A2B units.
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Affiliation(s)
- Rachel M Smith
- The DNA-protein Interactions Unit, School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, UK
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10
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Ershova AS, Karyagina AS, Vasiliev MO, Lyashchuk AM, Lunin VG, Spirin SA, Alexeevski AV. Solitary restriction endonucleases in prokaryotic genomes. Nucleic Acids Res 2012; 40:10107-15. [PMID: 22965118 PMCID: PMC3488263 DOI: 10.1093/nar/gks853] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Prokaryotic restriction-modification (R-M) systems defend the host cell from the invasion of a foreign DNA. They comprise two enzymatic activities: specific DNA cleavage activity and DNA methylation activity preventing cleavage. Typically, these activities are provided by two separate enzymes: a DNA methyltransferase (MTase) and a restriction endonuclease (RE). In the absence of a corresponding MTase, an RE of Type II R-M system is highly toxic for the cell. Genes of the R-M system are linked in the genome in the vast majority of annotated cases. There are only a few reported cases in which the genes of MTase and RE from one R-M system are not linked. Nevertheless, a few hundreds solitary RE genes are present in the Restriction Enzyme Database (http://rebase.neb.com) annotations. Using the comparative genomic approach, we analysed 272 solitary RE genes. For 57 solitary RE genes we predicted corresponding MTase genes located distantly in a genome. Of the 272 solitary RE genes, 99 are likely to be fragments of RE genes. Various explanations for the existence of the remaining 116 solitary RE genes are also discussed.
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Affiliation(s)
- Anna S Ershova
- Department of Mathematical Methods in Biology, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992, Moscow, Russia.
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11
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Roberts GA, Stephanou AS, Kanwar N, Dawson A, Cooper LP, Chen K, Nutley M, Cooper A, Blakely GW, Dryden DTF. Exploring the DNA mimicry of the Ocr protein of phage T7. Nucleic Acids Res 2012; 40:8129-43. [PMID: 22684506 PMCID: PMC3439906 DOI: 10.1093/nar/gks516] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Revised: 05/07/2012] [Accepted: 05/09/2012] [Indexed: 11/30/2022] Open
Abstract
DNA mimic proteins have evolved to control DNA-binding proteins by competing with the target DNA for binding to the protein. The Ocr protein of bacteriophage T7 is the most studied DNA mimic and functions to block the DNA-binding groove of Type I DNA restriction/modification enzymes. This binding prevents the enzyme from cleaving invading phage DNA. Each 116 amino acid monomer of the Ocr dimer has an unusual amino acid composition with 34 negatively charged side chains but only 6 positively charged side chains. Extensive mutagenesis of the charges of Ocr revealed a regression of Ocr activity from wild-type activity to partial activity then to variants inactive in antirestriction but deleterious for cell viability and lastly to totally inactive variants with no deleterious effect on cell viability. Throughout the mutagenesis the Ocr mutant proteins retained their folding. Our results show that the extreme bias in charged amino acids is not necessary for antirestriction activity but that less charged variants can affect cell viability by leading to restriction proficient but modification deficient cell phenotypes.
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Affiliation(s)
- Gareth A. Roberts
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Augoustinos S. Stephanou
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Nisha Kanwar
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Angela Dawson
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Laurie P. Cooper
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Kai Chen
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Margaret Nutley
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Alan Cooper
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Garry W. Blakely
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - David T. F. Dryden
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
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12
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Klaiman D, Steinfels-Kohn E, Krutkina E, Davidov E, Kaufmann G. The wobble nucleotide-excising anticodon nuclease RloC is governed by the zinc-hook and DNA-dependent ATPase of its Rad50-like region. Nucleic Acids Res 2012; 40:8568-78. [PMID: 22730290 PMCID: PMC3458546 DOI: 10.1093/nar/gks593] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
The conserved bacterial anticodon nuclease (ACNase) RloC and its phage-excluding homolog PrrC comprise respective ABC-adenosine triphosphatase (ATPase) and ACNase N- and C-domains but differ in three key attributes. First, prrC is always linked to an ACNase silencing, DNA restriction–modification (R–M) locus while rloC rarely features such linkage. Second, RloC excises its substrate’s wobble nucleotide, a lesion expected to impede damage reversal by phage transfer RNA (tRNA) repair enzymes that counteract the nick inflicted by PrrC. Third, a distinct coiled-coil/zinc-hook (CC/ZH) insert likens RloC’s N-region to the universal DNA damage checkpoint/repair protein Rad50. Previous work revealed that ZH mutations activate RloC’s ACNase. Data shown here suggest that RloC has an internal ACNase silencing/activating switch comprising its ZH and DNA-break-responsive ATPase. The existence of this control may explain the lateral transfer of rloC without an external silencer and supports the proposed role of RloC as an antiviral contingency acting when DNA restriction is alleviated under genotoxic stress. We also discuss RloC’s possible evolution from a PrrC-like ancestor.
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Affiliation(s)
- Daniel Klaiman
- Department of Biochemistry, Tel Aviv University, Tel Aviv 69978, Israel
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13
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Promiscuous restriction is a cellular defense strategy that confers fitness advantage to bacteria. Proc Natl Acad Sci U S A 2012; 109:E1287-93. [PMID: 22509013 DOI: 10.1073/pnas.1119226109] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Most bacterial genomes harbor restriction-modification systems, encoding a REase and its cognate MTase. On attack by a foreign DNA, the REase recognizes it as nonself and subjects it to restriction. Should REases be highly specific for targeting the invading foreign DNA? It is often considered to be the case. However, when bacteria harboring a promiscuous or high-fidelity variant of the REase were challenged with bacteriophages, fitness was maximal under conditions of catalytic promiscuity. We also delineate possible mechanisms by which the REase recognizes the chromosome as self at the noncanonical sites, thereby preventing lethal dsDNA breaks. This study provides a fundamental understanding of how bacteria exploit an existing defense system to gain fitness advantage during a host-parasite coevolutionary "arms race."
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14
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Kennaway CK, Taylor JE, Song CF, Potrzebowski W, Nicholson W, White JH, Swiderska A, Obarska-Kosinska A, Callow P, Cooper LP, Roberts GA, Artero JB, Bujnicki JM, Trinick J, Kneale GG, Dryden DT. Structure and operation of the DNA-translocating type I DNA restriction enzymes. Genes Dev 2012; 26:92-104. [PMID: 22215814 PMCID: PMC3258970 DOI: 10.1101/gad.179085.111] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Accepted: 11/14/2011] [Indexed: 11/24/2022]
Abstract
Type I DNA restriction/modification (RM) enzymes are molecular machines found in the majority of bacterial species. Their early discovery paved the way for the development of genetic engineering. They control (restrict) the influx of foreign DNA via horizontal gene transfer into the bacterium while maintaining sequence-specific methylation (modification) of host DNA. The endonuclease reaction of these enzymes on unmethylated DNA is preceded by bidirectional translocation of thousands of base pairs of DNA toward the enzyme. We present the structures of two type I RM enzymes, EcoKI and EcoR124I, derived using electron microscopy (EM), small-angle scattering (neutron and X-ray), and detailed molecular modeling. DNA binding triggers a large contraction of the open form of the enzyme to a compact form. The path followed by DNA through the complexes is revealed by using a DNA mimic anti-restriction protein. The structures reveal an evolutionary link between type I RM enzymes and type II RM enzymes.
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Affiliation(s)
- Christopher K. Kennaway
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - James E. Taylor
- Biophysics Laboratories, Institute of Biomedical and Biomolecular Sciences, School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, United Kingdom
| | - Chun Feng Song
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Wojciech Potrzebowski
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, PL-02-109 Warsaw, Poland
| | - William Nicholson
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - John H. White
- EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom
| | - Anna Swiderska
- Biophysics Laboratories, Institute of Biomedical and Biomolecular Sciences, School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, United Kingdom
| | - Agnieszka Obarska-Kosinska
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, PL-02-109 Warsaw, Poland
| | - Philip Callow
- Partnership for Structural Biology, Institut Laue-Langevin, Grenoble, Cedex 9, France
| | - Laurie P. Cooper
- EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom
| | - Gareth A. Roberts
- EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom
| | - Jean-Baptiste Artero
- Partnership for Structural Biology, Institut Laue-Langevin, Grenoble, Cedex 9, France
- EPSAM and ISTM, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
| | - Janusz M. Bujnicki
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, PL-02-109 Warsaw, Poland
- Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, PL-61-614 Poznan, Poland
| | - John Trinick
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - G. Geoff Kneale
- Biophysics Laboratories, Institute of Biomedical and Biomolecular Sciences, School of Biological Sciences, University of Portsmouth, Portsmouth PO1 2DY, United Kingdom
| | - David T.F. Dryden
- EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom
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15
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Simons M, Szczelkun MD. Recycling of protein subunits during DNA translocation and cleavage by Type I restriction-modification enzymes. Nucleic Acids Res 2011; 39:7656-66. [PMID: 21712244 PMCID: PMC3177213 DOI: 10.1093/nar/gkr479] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Type I restriction-modification enzymes comprise three protein subunits; HsdS and HsdM that form a methyltransferase (MTase) and HsdR that associates with the MTase and catalyses Adenosine-5′-triphosphate (ATP)-dependent DNA translocation and cleavage. Here, we examine whether the MTase and HsdR components can ‘turnover’ in vitro, i.e. whether they can catalyse translocation and cleavage events on one DNA molecule, dissociate and then re-bind a second DNA molecule. Translocation termination by both EcoKI and EcoR124I leads to HsdR dissociation from linear DNA but not from circular DNA. Following DNA cleavage, the HsdR subunits appear unable to dissociate even though the DNA is linear, suggesting a tight interaction with the cleaved product. The MTases of EcoKI and EcoAI can dissociate from DNA following either translocation or cleavage and can initiate reactions on new DNA molecules as long as free HsdR molecules are available. In contrast, the MTase of EcoR124I does not turnover and additional cleavage of circular DNA is not observed by inclusion of RecBCD, a helicase–nuclease that degrades the linear DNA product resulting from Type I cleavage. Roles for Type I restriction endonuclease subunit dynamics in restriction alleviation in the cell are discussed.
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Affiliation(s)
- Michelle Simons
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
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16
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Klaiman D, Kaufmann G. Phage T4-induced dTTP accretion bolsters a tRNase-based host defense. Virology 2011; 414:97-101. [PMID: 21481433 DOI: 10.1016/j.virol.2011.03.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Revised: 03/12/2011] [Accepted: 03/18/2011] [Indexed: 01/21/2023]
Abstract
The anticodon nuclease (ACNase) PrrC is silenced in Escherichia coli by an associated DNA restriction-modification protein, activated by the phage T4-encoded anti-DNA restriction factor Stp and counteracted by T4's tRNA repair enzymes polynucleotide kinase and RNA ligase 1. Hence, only tRNA repair-deficient phages succumb to PrrC's restriction. PrrC's ABC-ATPase motor domains are implicated in driving its activation by hydrolyzing GTP and in stabilizing the activated ACNase by avidly binding dTTP. The latter effect has been associated with dTTP's accumulation early in T4 infection when PrrC is activated. In agreement, delayed dTTP accumulation caused by dCMP deaminase deficiency coincided with impaired manifestation of PrrC's ACNase activity. This impairment did not suffice to suppress the PrrC-mediated restriction of tRNA repair deficient phage but was synthetically suppressive with a leaky stp mutation that only partly impairs PrrC's activation. Presumably, ability to gauge dTTP's changing level helps confine PrrC's toxicity to its viral target.
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Affiliation(s)
- Daniel Klaiman
- Department of Biochemistry, Tel Aviv University, Tel Aviv 69978, Israel
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17
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Ishikawa K, Handa N, Sears L, Raleigh EA, Kobayashi I. Cleavage of a model DNA replication fork by a methyl-specific endonuclease. Nucleic Acids Res 2011; 39:5489-98. [PMID: 21441537 PMCID: PMC3141261 DOI: 10.1093/nar/gkr153] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Epigenetic DNA methylation is involved in many biological processes. An epigenetic status can be altered by gain or loss of a DNA methyltransferase gene or its activity. Repair of DNA damage can also remove DNA methylation. In response to such alterations, DNA endonucleases that sense DNA methylation can act and may cause cell death. Here, we explored the possibility that McrBC, a methylation-dependent DNase of Escherichia coli, cleaves DNA at a replication fork. First, we found that in vivo restriction by McrBC of bacteriophage carrying a foreign DNA methyltransferase gene is increased in the absence of homologous recombination. This suggests that some cleavage events are repaired by recombination and must take place during or after replication. Next, we demonstrated that the enzyme can cleave a model DNA replication fork in vitro. Cleavage of a fork required methylation on both arms and removed one, the other or both of the arms. Most cleavage events removed the methylated sites from the fork. This result suggests that acquisition of even rarely occurring modification patterns will be recognized and rejected efficiently by modification-dependent restriction systems that recognize two sites. This process might serve to maintain an epigenetic status along the genome through programmed cell death.
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Affiliation(s)
- Ken Ishikawa
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, Shirokanedai, Tokyo 108-8639, Japan
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18
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Ishikawa K, Fukuda E, Kobayashi I. Conflicts targeting epigenetic systems and their resolution by cell death: novel concepts for methyl-specific and other restriction systems. DNA Res 2010; 17:325-42. [PMID: 21059708 PMCID: PMC2993543 DOI: 10.1093/dnares/dsq027] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Epigenetic modification of genomic DNA by methylation is important for defining the epigenome and the transcriptome in eukaryotes as well as in prokaryotes. In prokaryotes, the DNA methyltransferase genes often vary, are mobile, and are paired with the gene for a restriction enzyme. Decrease in a certain epigenetic methylation may lead to chromosome cleavage by the partner restriction enzyme, leading to eventual cell death. Thus, the pairing of a DNA methyltransferase and a restriction enzyme forces an epigenetic state to be maintained within the genome. Although restriction enzymes were originally discovered for their ability to attack invading DNAs, it may be understood because such DNAs show deviation from this epigenetic status. DNAs with epigenetic methylation, by a methyltransferase linked or unlinked with a restriction enzyme, can also be the target of DNases, such as McrBC of Escherichia coli, which was discovered because of its methyl-specific restriction. McrBC responds to specific genome methylation systems by killing the host bacterial cell through chromosome cleavage. Evolutionary and genomic analysis of McrBC homologues revealed their mobility and wide distribution in prokaryotes similar to restriction–modification systems. These findings support the hypothesis that this family of methyl-specific DNases evolved as mobile elements competing with specific genome methylation systems through host killing. These restriction systems clearly demonstrate the presence of conflicts between epigenetic systems.
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Affiliation(s)
- Ken Ishikawa
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo, Japan
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19
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Serfiotis-Mitsa D, Herbert AP, Roberts GA, Soares DC, White JH, Blakely GW, Uhrín D, Dryden DTF. The structure of the KlcA and ArdB proteins reveals a novel fold and antirestriction activity against Type I DNA restriction systems in vivo but not in vitro. Nucleic Acids Res 2009; 38:1723-37. [PMID: 20007596 PMCID: PMC2836571 DOI: 10.1093/nar/gkp1144] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Plasmids, conjugative transposons and phage frequently encode anti-restriction proteins to enhance their chances of entering a new bacterial host that is highly likely to contain a Type I DNA restriction and modification (RM) system. The RM system usually destroys the invading DNA. Some of the anti-restriction proteins are DNA mimics and bind to the RM enzyme to prevent it binding to DNA. In this article, we characterize ArdB anti-restriction proteins and their close homologues, the KlcA proteins from a range of mobile genetic elements; including an ArdB encoded on a pathogenicity island from uropathogenic Escherichia coli and a KlcA from an IncP-1b plasmid, pBP136 isolated from Bordetella pertussis. We show that all the ArdB and KlcA act as anti-restriction proteins and inhibit the four main families of Type I RM systems in vivo, but fail to block the restriction endonuclease activity of the archetypal Type I RM enzyme, EcoKI, in vitro indicating that the action of ArdB is indirect and very different from that of the DNA mimics. We also present the structure determined by NMR spectroscopy of the pBP136 KlcA protein. The structure shows a novel protein fold and it is clearly not a DNA structural mimic.
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Affiliation(s)
- Dimitra Serfiotis-Mitsa
- EaStChem School of Chemistry, University of Edinburgh, The King's Buildings, Edinburgh, EH9 3JJ, UK
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20
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Ishikawa K, Handa N, Kobayashi I. Cleavage of a model DNA replication fork by a Type I restriction endonuclease. Nucleic Acids Res 2009; 37:3531-44. [PMID: 19357093 PMCID: PMC2699502 DOI: 10.1093/nar/gkp214] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Cleavage of a DNA replication fork leads to fork restoration by recombination repair. In prokaryote cells carrying restriction-modification systems, fork passage reduces genome methylation by the modification enzyme and exposes the chromosome to attack by the restriction enzyme. Various observations have suggested a relationship between the fork and Type I restriction enzymes, which cleave DNA at a distance from a recognition sequence. Here, we demonstrate that a Type I restriction enzyme preparation cleaves a model replication fork at its branch. The enzyme probably tracks along the DNA from an unmethylated recognition site on the daughter DNA and cuts the fork upon encountering the branch point. Our finding suggests that these restriction-modification systems contribute to genome maintenance through cell death and indicates that DNA replication fork cleavage represents a critical point in genome maintenance to choose between the restoration pathway and the destruction pathway.
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Affiliation(s)
- Ken Ishikawa
- Graduate Program in Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 108-8639, Japan
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21
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RecBCD enzyme and the repair of double-stranded DNA breaks. Microbiol Mol Biol Rev 2009; 72:642-71, Table of Contents. [PMID: 19052323 DOI: 10.1128/mmbr.00020-08] [Citation(s) in RCA: 404] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The RecBCD enzyme of Escherichia coli is a helicase-nuclease that initiates the repair of double-stranded DNA breaks by homologous recombination. It also degrades linear double-stranded DNA, protecting the bacteria from phages and extraneous chromosomal DNA. The RecBCD enzyme is, however, regulated by a cis-acting DNA sequence known as Chi (crossover hotspot instigator) that activates its recombination-promoting functions. Interaction with Chi causes an attenuation of the RecBCD enzyme's vigorous nuclease activity, switches the polarity of the attenuated nuclease activity to the 5' strand, changes the operation of its motor subunits, and instructs the enzyme to begin loading the RecA protein onto the resultant Chi-containing single-stranded DNA. This enzyme is a prototypical example of a molecular machine: the protein architecture incorporates several autonomous functional domains that interact with each other to produce a complex, sequence-regulated, DNA-processing machine. In this review, we discuss the biochemical mechanism of the RecBCD enzyme with particular emphasis on new developments relating to the enzyme's structure and DNA translocation mechanism.
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22
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Structure of the motor subunit of type I restriction-modification complex EcoR124I. Nat Struct Mol Biol 2008; 16:94-5. [PMID: 19079266 DOI: 10.1038/nsmb.1523] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Accepted: 10/29/2008] [Indexed: 11/08/2022]
Abstract
Type I restriction-modification enzymes act as conventional adenine methylases on hemimethylated DNAs, but unmethylated recognition targets induce them to translocate thousands of base pairs before cleaving distant sites nonspecifically. The first crystal structure of a type I motor subunit responsible for translocation and cleavage suggests how the pentameric translocating complex is assembled and provides a structural framework for translocation of duplex DNA by RecA-like ATPase motors.
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23
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Mruk I, Blumenthal RM. Real-time kinetics of restriction-modification gene expression after entry into a new host cell. Nucleic Acids Res 2008; 36:2581-93. [PMID: 18334533 PMCID: PMC2377437 DOI: 10.1093/nar/gkn097] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Most type II restriction-modification (R-M) systems produce separate restriction endonuclease (REase) and methyltransferase (MTase) proteins. After R-M system genes enter a new cell, protective MTase must appear before REase to avoid host chromosome cleavage. The basis for this apparent temporal regulation is not well understood. PvuII and some other R-M systems appear to achieve this delay by cotranscribing the REase gene with the gene for an autogenous transcription activator/repressor (the 'C' protein C.PvuII). To test this model, bacteriophage M13 was used to introduce the PvuII genes into a bacterial population in a relatively synchronous manner. REase mRNA and activity appeared approximately 10 min after those of the MTase, but never rose if there was an inactivating pvuIIC mutation. Infection with recombinant M13pvuII phage had little effect on cell growth, relative to infection with parental M13. However, infection of cells pre-expressing C.PvuII led to cessation of growth. This study presents the first direct demonstration of delayed REase expression, relative to MTase, when type II R-M genes enter a new host cell. Surprisingly, though the C and REase genes are cotranscribed, the pvuIIC portion of the mRNA was more abundant than the pvuIIR portion after stable establishment of the R-M system.
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Affiliation(s)
- Iwona Mruk
- Department of Medical Microbiology and Immunology, University of Toledo Health Sciences Campus, Toledo, OH 43614-2598, USA.
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24
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Ivancić-Bacće I, Vlasić I, Cogelja-Cajo G, Brcić-Kostić K, Salaj-Smic E. Roles of PriA protein and double-strand DNA break repair functions in UV-induced restriction alleviation in Escherichia coli. Genetics 2006; 174:2137-49. [PMID: 17028321 PMCID: PMC1698619 DOI: 10.1534/genetics.106.063750] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been widely considered that DNA modification protects the chromosome of bacteria E. coli K-12 against their own restriction-modification systems. Chromosomal DNA is protected from degradation by methylation of target sequences. However, when unmethylated target sequences are generated in the host chromosome, the endonuclease activity of the EcoKI restriction-modification enzyme is inactivated by the ClpXP protease and DNA is protected. This process is known as restriction alleviation (RA) and it can be induced by UV irradiation (UV-induced RA). It has been proposed that chromosomal unmethylated target sequences, a signal for the cell to protect its own DNA, can be generated by homologous recombination during the repair of damaged DNA. In this study, we wanted to further investigate the genetic requirements for recombination proteins involved in the generation of unmethylated target sequences. For this purpose, we monitored the alleviation of EcoKI restriction by measuring the survival of unmodified lambda in UV-irradiated cells. Our genetic analysis showed that UV-induced RA is dependent on the excision repair protein UvrA, the RecA-loading activity of the RecBCD enzyme, and the primosome assembly activity of the PriA helicase and is partially dependent on RecFOR proteins. On the basis of our results, we propose that unmethylated target sequences are generated at the D-loop by the strand exchange of two hemi-methylated duplex DNAs and subsequent initiation of DNA replication.
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Affiliation(s)
- Ivana Ivancić-Bacće
- Department of Molecular Biology, Faculty of Science, University of Zagreb, Croatia.
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25
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Blakely GW, Murray NE. Control of the endonuclease activity of type I restriction-modification systems is required to maintain chromosome integrity following homologous recombination. Mol Microbiol 2006; 60:883-93. [PMID: 16677300 DOI: 10.1111/j.1365-2958.2006.05144.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
A type I restriction-modification enzyme will bind to an unmethylated target sequence in DNA and, while still bound to the target, translocate DNA through the protein complex in both directions. DNA breakage occurs when two translocating complexes collide. However, if type I restriction-modification systems bind to unmodified target sequences within the resident bacterial chromosome, as opposed to incoming 'foreign' DNA, their activity is curtailed; a process known as restriction alleviation (RA). We have identified two genes in Escherichia coli, rnhA and recG, mutations in which lead to the alleviation of restriction. Induction of RA in response to these mutations is consistent with the production of unmodified target sequences following DNA synthesis associated with both homologous recombination and R-loop formation. This implies that a normal function of RA is to protect the bacterial chromosome when recombination generates unmodified products. For EcoKI, our experiments demonstrate the contribution of two pathways that serve to protect unmodified DNA in the bacterial chromosome: the primary pathway in which ClpXP degrades the restriction endonuclease and a mechanism dependent on the lar gene within Rac, a resident, defective prophage of E. coli K-12. Previously, the potential of the second pathway has only been demonstrated when expression of lar has been elevated. Our data identify the effect of lar from the repressed prophage.
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Affiliation(s)
- Garry W Blakely
- Institute of Structural and Molecular Biology, University of Edinburgh, Edinburgh, Scotland, UK.
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26
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Flyvbjerg H, Keatch SA, Dryden DT. Strong physical constraints on sequence-specific target location by proteins on DNA molecules. Nucleic Acids Res 2006; 34:2550-7. [PMID: 16698961 PMCID: PMC3303175 DOI: 10.1093/nar/gkl271] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Sequence-specific binding to DNA in the presence of competing non-sequence-specific ligands is a problem faced by proteins in all organisms. It is akin to the problem of parking a truck at a loading bay by the side of a road in the presence of cars parked at random along the road. Cars even partially covering the loading bay prevent correct parking of the truck. Similarly on DNA, non-specific ligands interfere with the binding and function of sequence-specific proteins. We derive a formula for the probability that the loading bay is free from parked cars. The probability depends on the size of the loading bay and allows an estimation of the size of the footprint on the DNA of the sequence-specific protein by assaying protein binding or function in the presence of increasing concentrations of non-specific ligand. Assaying for function gives an 'activity footprint'; the minimum length of DNA required for function rather than the more commonly measured physical footprint. Assaying the complex type I restriction enzyme, EcoKI, gives an activity footprint of approximately 66 bp for ATP hydrolysis and 300 bp for the DNA cleavage function which is intimately linked with translocation of DNA by EcoKI. Furthermore, considering the coverage of chromosomal DNA by proteins in vivo, our theory shows that the search for a specific DNA sequence is very difficult; most sites are obscured by parked cars. This effectively rules out any significant role in target location for mechanisms invoking one-dimensional, linear diffusion along DNA.
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Affiliation(s)
- Henrik Flyvbjerg
- Risø National Laboratory, Biosystems Department and Danish Polymer Centre Building BIO-776, PO Box 49, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
- Isaac Newton Institute for Mathematical Sciences 20 Clarkson Road, Cambridge, CB3 0EH, UK
| | - Steven A. Keatch
- School of Chemistry, The King's Buildings, The University of Edinburgh Edinburgh, EH9 3JJ, UK
| | - David T.F. Dryden
- School of Chemistry, The King's Buildings, The University of Edinburgh Edinburgh, EH9 3JJ, UK
- Isaac Newton Institute for Mathematical Sciences 20 Clarkson Road, Cambridge, CB3 0EH, UK
- To whom correspondence should be adressed. Tel: +0131 650 4735; Fax: +0131 650 6453;
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27
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Stanley LK, Seidel R, van der Scheer C, Dekker NH, Szczelkun MD, Dekker C. When a helicase is not a helicase: dsDNA tracking by the motor protein EcoR124I. EMBO J 2006; 25:2230-9. [PMID: 16642041 PMCID: PMC1462981 DOI: 10.1038/sj.emboj.7601104] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2006] [Accepted: 03/27/2006] [Indexed: 11/08/2022] Open
Abstract
Using a combination of single molecule and bulk solution measurements, we have examined the DNA translocation activity of a helicase, the Type I restriction modification enzyme EcoR124I. We find that EcoR124I can translocate past covalent interstrand crosslinks, inconsistent with an obligatory unwinding mechanism. Instead, translocation of the intact dsDNA occurs principally via contacts to the sugar-phosphate backbone and bases of the 3'-5' strand; contacts to the 5'-3' strand are not essential for motion but do play a key role in stabilising the motor on the DNA. A model for dsDNA translocation is presented that could be applicable to a wide range of other enzyme complexes that are also labelled as helicases but which do not have actual unwinding activity.
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Affiliation(s)
- Louise K Stanley
- DNA–Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, UK
| | - Ralf Seidel
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | | | - Nynke H Dekker
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Mark D Szczelkun
- DNA–Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, UK
- DNA-Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK. Tel.: +44 117 928 7439; Fax: +44 117 928 8274; E-mail:
| | - Cees Dekker
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands. Tel.: +31 15 278 6094; Fax: +31 15 278 1202; E-mail:
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28
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O'Driscoll J, Fitzgerald GF, van Sinderen D. A dichotomous epigenetic mechanism governs expression of the LlaJI restriction/modification system. Mol Microbiol 2005; 57:1532-44. [PMID: 16135222 DOI: 10.1111/j.1365-2958.2005.04769.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The LlaJI restriction/modification (R/M) system is comprised of two 5mC MTase-encoding genes, llaJIM1 and llaJIM2, and two genes required for restriction activity, llaJIR1 and llaJIR2. Here, we report the molecular mechanism by which this R/M system is transcriptionally regulated. The recognition sequence for the LlaJI MTases was deduced to be 5'GACGC'3 for M1.LlaJI and 5'GCGTC'3 for M2.LlaJI, thus together constituting an asymmetric complementary recognition site. Two recognition sequences for both LlaJI MTases are present within the LlaJI promoter region, indicative of an epigenetic role. Following in vivo analysis of expression of the LlaJI promoter, we established that both LlaJI MTases were required for complete transcriptional repression. A mutational analysis and DNA binding studies of this promoter revealed that the methylation of two specific cytosines by M2.LlaJI within this region was required to trigger the specific and high affinity binding of M1.LlaJI, which serves to regulate expression of the LlaJI operon. This regulatory system therefore represents the amalgamation of an epigenetic stimulation coupled to the formation of a MTase/repressor:promoter complex.
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29
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Keatch SA, Leonard PG, Ladbury JE, Dryden DTF. StpA protein from Escherichia coli condenses supercoiled DNA in preference to linear DNA and protects it from digestion by DNase I and EcoKI. Nucleic Acids Res 2005; 33:6540-6. [PMID: 16299353 PMCID: PMC1289078 DOI: 10.1093/nar/gki951] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The nucleoid-associated protein, StpA, of Escherichia coli binds non-specifically to double-stranded DNA (dsDNA) and apparently forms bridges between adjacent segments of the DNA. Such a coating of protein on the DNA would be expected to hinder the action of nucleases. We demonstrate that StpA binding hinders dsDNA cleavage by both the non-specific endonuclease, DNase I, and by the site-specific type I restriction endonuclease, EcoKI. It requires approximately one StpA molecule per 250–300 bp of supercoiled DNA and approximately one StpA molecule per 60–100 bp on linear DNA for strong inhibition of the nucleases. These results support the role of StpA as a nucleoid-structuring protein which binds DNA segments together. The inhibition of EcoKI, which cleaves DNA at a site remote from its initial target sequence after extensive DNA translocation driven by ATP hydrolysis, suggests that these enzymes would be unable to function on chromosomal DNA even during times of DNA damage when potentially lethal, unmodified target sites occur on the chromosome. This supports a role for nucleoid-associated proteins in restriction alleviation during times of cell stress.
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Affiliation(s)
| | - P. G. Leonard
- Department of Biochemistry and Molecular Biology, University College LondonGower Street, London WC1E 6BT, UK
| | - J. E. Ladbury
- Department of Biochemistry and Molecular Biology, University College LondonGower Street, London WC1E 6BT, UK
| | - D. T. F. Dryden
- To whom correspondence should be addressed. Tel: +44 131 650 4735; Fax: +44 131 650 6453;
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30
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Seidel R, Bloom JGP, van Noort J, Dutta CF, Dekker NH, Firman K, Szczelkun MD, Dekker C. Dynamics of initiation, termination and reinitiation of DNA translocation by the motor protein EcoR124I. EMBO J 2005; 24:4188-97. [PMID: 16292342 PMCID: PMC1356320 DOI: 10.1038/sj.emboj.7600881] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Accepted: 10/28/2005] [Indexed: 11/09/2022] Open
Abstract
Type I restriction enzymes use two motors to translocate DNA before carrying out DNA cleavage. The motor function is accomplished by amino-acid motifs typical for superfamily 2 helicases, although DNA unwinding is not observed. Using a combination of extensive single-molecule magnetic tweezers and stopped-flow bulk measurements, we fully characterized the (re)initiation of DNA translocation by EcoR124I. We found that the methyltransferase core unit of the enzyme loads the motor subunits onto adjacent DNA by allowing them to bind and initiate translocation. Termination of translocation occurs owing to dissociation of the motors from the core unit. Reinitiation of translocation requires binding of new motors from solution. The identification and quantification of further initiation steps--ATP binding and extrusion of an initial DNA loop--allowed us to deduce a complete kinetic reinitiation scheme. The dissociation/reassociation of motors during translocation allows dynamic control of the restriction process by the availability of motors. Direct evidence that this control mechanism is relevant in vivo is provided.
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Affiliation(s)
- Ralf Seidel
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Joost G P Bloom
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - John van Noort
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Christina F Dutta
- School of Biological Sciences, University of Portsmouth, Portsmouth, UK
| | - Nynke H Dekker
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Keith Firman
- School of Biological Sciences, University of Portsmouth, Portsmouth, UK
| | - Mark D Szczelkun
- Department of Biochemistry, School of Medical Sciences, Bristol, UK
- Department of Biochemistry, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK. Tel.: +44 117 928 7439; Fax: +44 117 928 8274; E-mail:
| | - Cees Dekker
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands. Tel.: +31 15 278 6094; Fax: +31 15 278 1202; E-mail:
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31
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Tock MR, Dryden DTF. The biology of restriction and anti-restriction. Curr Opin Microbiol 2005; 8:466-72. [PMID: 15979932 DOI: 10.1016/j.mib.2005.06.003] [Citation(s) in RCA: 363] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2005] [Accepted: 06/09/2005] [Indexed: 11/29/2022]
Abstract
The phenomena of prokaryotic restriction and modification, as well as anti-restriction, were first discovered five decades ago but have yielded only gradually to rigorous analysis. Work presented at the 5th New England Biolabs Meeting on Restriction-Modification (available on REBASE, http://www.rebase.com) and several recently published genetic, biochemical and biophysical analyses indicate that these fields continue to contribute significantly to basic science. Recently, there have been several studies that have shed light on the still developing field of restriction-modification and on the newly re-emerging field of anti-restriction.
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Affiliation(s)
- Mark R Tock
- School of Chemistry, The King's Buildings, The University of Edinburgh, Edinburgh, EH9 3JJ, UK
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32
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Sears A, Szczelkun MD. Subunit assembly modulates the activities of the Type III restriction-modification enzyme PstII in vitro. Nucleic Acids Res 2005; 33:4788-96. [PMID: 16120968 PMCID: PMC1192831 DOI: 10.1093/nar/gki788] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We demonstrate that, like other Type III restriction endonuclease, PstII does not turnover such that a DNA substrate is only fully cleaved at a Res2Mod2-to-site ratio of approximately 1:1. However, unlike other Type III enzymes, the cleavage rate profiles varied with protein concentration: using 5 nM DNA and 25 nM PstII, approximately half of the DNA was cut at a fast rate while the remainder was cut 24 times more slowly; in comparison, with 100 nM PstII cleavage occurs at a single fast rate. The inclusion of the methyl donor S-adenosyl methionine does not alter the rates with 100 nM PstII but with 25 nM PstII the reaction stopped after completion of the initial fast cleavage phase owing to methylation. Concentration-dependent rates were also observed in methylation assays: at 100 nM PstII, a single slow rate was measured while at lower PstII concentrations both fast and slow rates were measured. We propose a model in which the intact Res2Mod2 complex favoured at high PstII concentrations is a fast endonuclease/slow methyltransferase while the various subassemblies which coexist at lower concentrations are fast methyltransferases. A potential role for disassembly in control of restriction activity in vivo is discussed.
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Affiliation(s)
| | - Mark D. Szczelkun
- To whom correspondence should be addressed. Tel: +44 117 928 7439; Fax: +44 117 928 8274;
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33
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McClelland SE, Dryden DTF, Szczelkun MD. Continuous assays for DNA translocation using fluorescent triplex dissociation: application to type I restriction endonucleases. J Mol Biol 2005; 348:895-915. [PMID: 15843021 DOI: 10.1016/j.jmb.2005.03.018] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2004] [Revised: 02/14/2005] [Accepted: 03/04/2005] [Indexed: 11/25/2022]
Abstract
Fluorescent assays and accompanying kinetic models are described for the analysis of DNA translocation independent of duplex unwinding. A triplex binding site (TBS) was introduced into DNA substrates at precise loci downstream of recognition sequences for type IA, IB and IC restriction endonucleases (EcoKI, EcoAI and EcoR124I, respectively). Each endonuclease was incubated (without ATP) with substrates on which a hexachlorofluoroscein-labelled triplex-forming oligonucleotide (HEX-TFO) was pre-bound. Following addition of ATP, 1-D enzyme motion resulted in collision with, and displacement of, the HEX-TFO, producing a >twofold increase in fluorescent intensity. Alternatively, a decrease in anisotropy following displacement of a rhodamine-labelled TFO was monitored. Using rapid mixing in a stopped-flow fluorimeter, continuous kinetic profiles were produced in which displacement is preceded by a lag-phase, directly proportional to the distance moved. For each enzyme, we obtained not only the translocation rate but also information on slow isomerisation step(s) at initiation. Furthermore, we demonstrated that enzymes deficient in DNA cleavage but with maximal ATPase activity showed initiation and translocation rates identical to wild-type, confirming that DNA strand breaks are not a pre-requisite of motion.
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Affiliation(s)
- Sarah E McClelland
- DNA-Protein Interactions Group, Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
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34
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Keatch SA, Su TJ, Dryden DTF. Alleviation of restriction by DNA condensation and non-specific DNA binding ligands. Nucleic Acids Res 2004; 32:5841-50. [PMID: 15520467 PMCID: PMC528803 DOI: 10.1093/nar/gkh918] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
During conditions of cell stress, the type I restriction and modification enzymes of bacteria show reduced, but not zero, levels of restriction of unmethylated foreign DNA. In such conditions, chemically identical unmethylated recognition sequences also occur on the chromosome of the host but restriction alleviation prevents the enzymes from destroying the host DNA. How is this distinction between chemically identical DNA molecules achieved? For some, but not all, type I restriction enzymes, alleviation is partially due to proteolytic degradation of a subunit of the enzyme. We identify that the additional alleviation factor is attributable to the structural difference between foreign DNA entering the cell as a random coil and host DNA, which exists in a condensed nucleoid structure coated with many non-specific ligands. The type I restriction enzyme is able to destroy the 'naked' DNA using a complex reaction linked to DNA translocation, but this essential translocation process is inhibited by DNA condensation and the presence of non-specific ligands bound along the DNA.
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Affiliation(s)
- Steven A Keatch
- School of Chemistry, The University of Edinburgh, The King's Buildings, Edinburgh, EH9 3JJ, UK
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35
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Seidel R, van Noort J, van der Scheer C, Bloom JGP, Dekker NH, Dutta CF, Blundell A, Robinson T, Firman K, Dekker C. Real-time observation of DNA translocation by the type I restriction modification enzyme EcoR124I. Nat Struct Mol Biol 2004; 11:838-43. [PMID: 15300241 DOI: 10.1038/nsmb816] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2004] [Accepted: 07/14/2004] [Indexed: 11/10/2022]
Abstract
Type I restriction enzymes bind sequence-specifically to unmodified DNA and subsequently pull the adjacent DNA toward themselves. Cleavage then occurs remotely from the recognition site. The mechanism by which these members of the superfamily 2 (SF2) of helicases translocate DNA is largely unknown. We report the first single-molecule study of DNA translocation by the type I restriction enzyme EcoR124I. Mechanochemical parameters such as the translocation rate and processivity, and their dependence on force and ATP concentration, are presented. We show that the two motor subunits of EcoR124I work independently. By using torsionally constrained DNA molecules, we found that the enzyme tracks along the helical pitch of the DNA molecule. This assay may be directly applicable to investigating the tracking of other DNA-translocating motors along their DNA templates.
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Affiliation(s)
- Ralf Seidel
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
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36
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Holubová I, Vejsadová S, Firman K, Weiserová M. Cellular localization of Type I restriction-modification enzymes is family dependent. Biochem Biophys Res Commun 2004; 319:375-80. [PMID: 15178416 DOI: 10.1016/j.bbrc.2004.04.184] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2004] [Indexed: 11/28/2022]
Abstract
Cellular localization of Type I restriction-modification enzymes EcoKI, EcoAI, and EcoR124I-the most frequently studied representatives of IA, IB, and IC families-was analyzed by immunoblotting of subcellular fractions isolated from Escherichia coli strains harboring the corresponding hsd genes. EcoR124I shows characteristics similar to those of EcoKI. The complex enzymes are associated with the cytoplasmic membrane via DNA interaction as documented by the release of the Hsd subunits from the membrane into the soluble fraction following benzonase treatment. HsdR subunits of the membrane-bound enzymes EcoKI and EcoR124I are accessible, though to a different extent, at the external surface of cytoplasmic membrane as shown by trypsinization of intact spheroplasts. EcoAI strongly differs from EcoKI and EcoR124I, since neither benzonase nor trypsin affects its association with the cytoplasmic membrane. Possible reasons for such a different organization are discussed in relation of the control of the restriction-modification activities in vivo.
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Affiliation(s)
- I Holubová
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Prague
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37
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Abstract
Systems biology is a new, fashionable and well-funded discipline, which to quote from a recent review aims to 'examine the structure and dynamics of cellular and organismal function, rather than the characteristics of isolated parts of a cell or organism em leader ' (Kitano, H. (2002) Science 295:1662-1664). Systems biology will do this by profiting from the vast amounts of biological information that are available in the genomics era and make extensive use of computer modelling. But: 'many breakthroughs in experimental devices, advanced software and analytical methods are required before the achievements of system biology can live up to their much-touted potential'. This edition of Molecular Microbiology contains a paper that is the product of traditional experimental biology but which could serve as a test case for systems biology. The paper shows how bacteria integrate such disparate subsystems as DNA restriction, homologous recombination and regulated proteolysis to protect their chromosomes from degradation. When systems biology can predict this level of choreography, it will be a mature discipline.
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Affiliation(s)
- Thomas A Bickle
- Division of Molecular Microbiology, Biozentrum, Basel University, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
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38
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Loenen WAM. Tracking EcoKI and DNA fifty years on: a golden story full of surprises. Nucleic Acids Res 2004; 31:7059-69. [PMID: 14654681 PMCID: PMC291878 DOI: 10.1093/nar/gkg944] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
1953 was a historical year for biology, as it marked the birth of the DNA helix, but also a report by Bertani and Weigle on 'a barrier to infection' of bacteriophage lambda in its natural host, Escherichia coli K-12, that could be lifted by 'host-controlled variation' of the virus. This paper lay dormant till Nobel laureate Arber and PhD student Dussoix showed that the lambda DNA was rejected and degraded upon infection of different bacterial hosts, unless it carried host-specific modification of that DNA, thus laying the foundations for the phenomenon of restriction and modification (R-M). The restriction enzyme of E.coli K-12, EcoKI, was purified in 1968 and required S-adenosylmethionine (AdoMet) and ATP as cofactors. By the end of the decade there was substantial evidence for a chromosomal locus hsdK with three genes encoding restriction (R), modification (M) and specificity (S) subunits that assembled into a large complex of >400 kDa. The 1970s brought the message that EcoKI cut away from its DNA recognition target, to which site the enzyme remained bound while translocating the DNA past itself, with concomitant ATP hydrolysis and subsequent double-strand nicks. This translocation event created clearly visible DNA loops in the electron microscope. EcoKI became the archetypal Type I R-M enzyme with curious DNA translocating properties reminiscent of helicases, recognizing the bipartite asymmetric site AAC(N6)GTGC. Cloning of the hsdK locus in 1976 facilitated molecular understanding of this sophisticated R-M complex and in an elegant 'pas de deux' Murray and Dryden constructed the present model based on a large body of experimental data plus bioinformatics. This review celebrates the golden anniversary of EcoKI and ends with the exciting progress on the vital issue of restriction alleviation after DNA damage, also first reported in 1953, which involves intricate control of R subunit activity by the bacterial proteasome ClpXP, important results that will keep scientists on the EcoKI track for another 50 years to come.
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Affiliation(s)
- Wil A M Loenen
- Department of Medical Microbiology, University Maastricht, Maastricht, The Netherlands.
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