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Tabib-Salazar A, Mulvenna N, Severinov K, Matthews SJ, Wigneshweraraj S. Xenogeneic Regulation of the Bacterial Transcription Machinery. J Mol Biol 2019; 431:4078-4092. [DOI: 10.1016/j.jmb.2019.02.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Revised: 01/30/2019] [Accepted: 02/06/2019] [Indexed: 10/27/2022]
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Tabib-Salazar A, Liu B, Shadrin A, Burchell L, Wang Z, Wang Z, Goren MG, Yosef I, Qimron U, Severinov K, Matthews SJ, Wigneshweraraj S. Full shut-off of Escherichia coli RNA-polymerase by T7 phage requires a small phage-encoded DNA-binding protein. Nucleic Acids Res 2017; 45:7697-7707. [PMID: 28486695 PMCID: PMC5569994 DOI: 10.1093/nar/gkx370] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Accepted: 04/24/2017] [Indexed: 11/13/2022] Open
Abstract
Infection of Escherichia coli by the T7 phage leads to rapid and selective inhibition of the bacterial RNA polymerase (RNAP) by the 7 kDa T7 protein Gp2. We describe the identification and functional and structural characterisation of a novel 7 kDa T7 protein, Gp5.7, which adopts a winged helix-turn-helix-like structure and specifically represses transcription initiation from host RNAP-dependent promoters on the phage genome via a mechanism that involves interaction with DNA and the bacterial RNAP. Whereas Gp2 is indispensable for T7 growth in E. coli, we show that Gp5.7 is required for optimal infection outcome. Our findings provide novel insights into how phages fine-tune the activity of the host transcription machinery to ensure both successful and efficient phage progeny development.
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Affiliation(s)
- Aline Tabib-Salazar
- MRC Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Bing Liu
- MRC Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Andrey Shadrin
- G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow 142290, Russia
| | - Lynn Burchell
- MRC Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Zhexin Wang
- MRC Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Zhihao Wang
- MRC Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Moran G Goren
- Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | - Ido Yosef
- Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | - Udi Qimron
- Department of Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | - Konstantin Severinov
- Waksman Institute of Microbiology, Rutgers, The State University of New Jersey, 190 Frelinghuysen Road, Piscataway, NJ 08854-8020, USA
| | - Steve J Matthews
- MRC Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
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Abstract
I spent my childhood and adolescence in North and South Carolina, attended Duke University, and then entered Duke Medical School. One year in the laboratory of George Schwert in the biochemistry department kindled my interest in biochemistry. After one year of residency on the medical service of Duke Hospital, chaired by Eugene Stead, I joined the group of Arthur Kornberg at Stanford Medical School as a postdoctoral fellow. Two years later I accepted a faculty position at Harvard Medical School, where I remain today. During these 50 years, together with an outstanding group of students, postdoctoral fellows, and collaborators, I have pursued studies on DNA replication. I have experienced the excitement of discovering a number of important enzymes in DNA replication that, in turn, triggered an interest in the dynamics of a replisome. My associations with industry have been stimulating and fostered new friendships. I could not have chosen a better career.
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Affiliation(s)
- Charles C Richardson
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115;
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Sheppard C, James E, Barton G, Matthews S, Severinov K, Wigneshweraraj S. A non-bacterial transcription factor inhibits bacterial transcription by a multipronged mechanism. RNA Biol 2013; 10:495-501. [PMID: 23558648 DOI: 10.4161/rna.24283] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The process of transcription initiation is the major target for regulation of gene expression in bacteria and is performed by a multi-subunit RNA polymerase enzyme (RNAp). A complex network of regulatory elements controls the activity of the RNAp to fine-tune transcriptional output. Thus, RNAp is a nexus for controlling bacterial gene expression at the transcription level. Many bacteriophages, viruses that infect bacteria, encode transcription factors that specifically target and modulate the activity of the host RNAp and, thereby, facilitate the acquisition of the host bacteria by the phage. Here, we describe the modus operandi of a T7 bacteriophage-encoded small protein called Gp2 and define Gp2 as a non-bacterial regulator of bacterial transcription.
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Affiliation(s)
- Carol Sheppard
- MRC Centre for Molecular Bacteriology and Infection, Faculty of Medicine, Imperial College London, London, UK
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Klimuk E, Akulenko N, Makarova KS, Ceyssens PJ, Volchenkov I, Lavigne R, Severinov K. Host RNA polymerase inhibitors encoded by ϕKMV-like phages of pseudomonas. Virology 2013; 436:67-74. [DOI: 10.1016/j.virol.2012.10.021] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Revised: 09/27/2012] [Accepted: 10/11/2012] [Indexed: 11/30/2022]
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Savalia D, Robins W, Nechaev S, Molineux I, Severinov K. The role of the T7 Gp2 inhibitor of host RNA polymerase in phage development. J Mol Biol 2010; 402:118-26. [PMID: 20650282 DOI: 10.1016/j.jmb.2010.07.012] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Revised: 07/05/2010] [Accepted: 07/12/2010] [Indexed: 11/19/2022]
Abstract
Bacteriophage T7 relies on its own RNA polymerase (RNAp) to transcribe its middle and late genes. Early genes, which include the viral RNAp gene, are transcribed by the host RNAp from three closely spaced strong promoters-A1, A2, and A3. One middle T7 gene product, gp2, is a strong inhibitor of the host RNAp. Gp2 is essential and is required late in infection, during phage DNA packaging. Here, we explore the role of gp2 in controlling host RNAp transcription during T7 infection. We demonstrate that in the absence of gp2, early viral transcripts continue to accumulate throughout the infection. Decreasing transcription from early promoter A3 is sufficient to make gp2 dispensable for phage infection. Gp2 also becomes dispensable when an antiterminating element boxA, located downstream of early promoters, is deleted. The results thus suggest that antiterminated transcription by host RNAp from the A3 promoter is interfering with phage development and that the only essential role for gp2 is to prevent this transcription.
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Affiliation(s)
- Dhruti Savalia
- Waksman Institute for Microbiology, 190 Frelinghuysen Road, Piscataway, NJ 08854, USA
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Roucourt B, Lavigne R. The role of interactions between phage and bacterial proteins within the infected cell: a diverse and puzzling interactome. Environ Microbiol 2009; 11:2789-805. [PMID: 19691505 DOI: 10.1111/j.1462-2920.2009.02029.x] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Interactions between bacteriophage proteins and bacterial proteins are important for efficient infection of the host cell. The phage proteins involved in these bacteriophage-host interactions are often produced immediately after infection. A survey of the available set of published bacteriophage-host interactions reveals the targeted host proteins are inhibited, activated or functionally redirected by the phage protein. These interactions protect the bacteriophage from bacterial defence mechanisms or adapt the host-cell metabolism to establish an efficient infection cycle. Regrettably, a large majority of bacteriophage early proteins lack any identified function. Recent research into the antibacterial potential of bacteriophage-host interactions indicates that phage early proteins seem to target a wide variety of processes in the host cell - many of them non-essential. Since a clear understanding of such interactions may become important for regulations involving phage therapy and in biotechnological applications, increased scientific emphasis on the biological elucidation of such proteins is warranted.
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Affiliation(s)
- Bart Roucourt
- Division of Gene Technology, Department of Biosystems, Katholieke Universiteit Leuven, Kasteelpark Arenberg 21 box 2462, B-3001 Leuven, Belgium
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Nechaev S, Severinov K. The elusive object of desire--interactions of bacteriophages and their hosts. Curr Opin Microbiol 2008; 11:186-93. [PMID: 18400552 DOI: 10.1016/j.mib.2008.02.009] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Revised: 02/18/2008] [Accepted: 02/21/2008] [Indexed: 12/27/2022]
Abstract
Bacteria and their viruses (phages) are locked in an evolutionary contest, with each side producing constantly changing mechanisms of attack and defense that are aimed to increase the odds of survival. As a result, phages play central roles in a great variety of genetic processes and increase the rate of evolutionary change of the bacterial host, which could ultimately work to the benefit of the host in a long run.
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Affiliation(s)
- Sergei Nechaev
- Laboratory of Molecular Carcinogenesis, NIEHS/NIH, Room D434, 111 Alexander Dr, Research Triangle Park, NC 27709, USA.
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Qimron U, Kulczyk AW, Hamdan SM, Tabor S, Richardson CC. Inadequate inhibition of host RNA polymerase restricts T7 bacteriophage growth on hosts overexpressing udk. Mol Microbiol 2007; 67:448-57. [PMID: 18067538 DOI: 10.1111/j.1365-2958.2007.06058.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Overexpression of udk, an Escherichia coli gene encoding a uridine/cytidine kinase, interferes with T7 bacteriophage growth. We show here that inhibition of T7 phage growth by udk overexpression can be overcome by inhibition of host RNA polymerase. Overexpression of gene 2, whose product inhibits host RNA polymerase, restores T7 phage growth on hosts overexpressing udk. In addition, rifampicin, an inhibitor of host RNA polymerase, restores the burst size of T7 phage on udk-overexpressing hosts to normal. In agreement with these findings, suppressor mutants that overcome the inhibition arising from udk overexpression gain the ability to grow on hosts that are resistant to inhibition of RNA polymerase by gene 2 protein, and suppressor mutants that overcome a lack of gene 2 protein gain the ability to grow on hosts that overexpress udk. Mutations that eliminate or weaken strong promoters for host RNA polymerase in T7 DNA, and mutations in T7 gene 3.5 that affect its interaction with T7 RNA polymerase, also reduce the interference with T7 growth by host RNA polymerase. We propose a general model for the requirement of host RNA polymerase inhibition.
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Affiliation(s)
- Udi Qimron
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
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Qimron U, Marintcheva B, Tabor S, Richardson CC. Genomewide screens for Escherichia coli genes affecting growth of T7 bacteriophage. Proc Natl Acad Sci U S A 2006; 103:19039-44. [PMID: 17135349 PMCID: PMC1748173 DOI: 10.1073/pnas.0609428103] [Citation(s) in RCA: 154] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2006] [Indexed: 11/18/2022] Open
Abstract
Use of bacteriophages as a therapy for bacterial infection has been attempted over the last century. Such an endeavor requires the elucidation of basic aspects of the host-virus interactions and the resistance mechanisms of the host. Two recently developed bacterial collections now enable a genomewide search of the genetic interactions between Escherichia coli and bacteriophages. We have screened >85% of the E. coli genes for their ability to inhibit growth of T7 phage and >90% of the host genes for their ability to be used by the virus. In addition to identifying all of the known interactions, several other interactions have been identified. E. coli CMP kinase is essential for T7 growth, whereas overexpression of the E. coli uridine/cytidine kinase inhibits T7 growth. Mutations in any one of nine genes that encode enzymes for the synthesis of the E. coli lipopolysaccharide receptor for T7 adsorption leads to T7 resistance. Selection of T7 phage that can recognize these altered receptors has enabled the construction of phage to which the host is 100-fold less resistant.
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Affiliation(s)
- Udi Qimron
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Boriana Marintcheva
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Stanley Tabor
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Charles C. Richardson
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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12
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Nechaev S, Severinov K. Inhibition of Escherichia coli RNA polymerase by bacteriophage T7 gene 2 protein. J Mol Biol 1999; 289:815-26. [PMID: 10369763 DOI: 10.1006/jmbi.1999.2782] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The 64 amino acid residue product of bacteriophage T7 gene 2 (gp2) binds the Escherichia coli RNA polymerase and inhibits transcription. We localized the gp2 binding site to within 53 amino acid residues in the functionally dispensable region of the RNA polymerase beta' subunit. We investigated the effect of gp2 on transcription at a -10/-35 promoter and at an "extended -10" promoter. Our results indicate that binding of gp2 to the sigma70holoenzyme (Esigma70) prevents promoter recognition at -10/-35 promoters. Once open promoter complexes are formed, however, Esigma70transcription is resistant to gp2, since gp2 can no longer bind RNA polymerase. Surprisingly, transcription inhibition by gp2 is both sigma and promoter-specific. gp2 has little effect on Esigma70transcription from an extended -10 promoter, which does not depend on sigma70region 4 interactions with the -35 promoter box for its activity. gp55-dependent phage T4 late promoter transcription is also resistant to gp2. From these results, we conclude that the interaction of the sigma70region 4 with the -35 consensus promoter element is the primary target of gp2 inhibition.
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Affiliation(s)
- S Nechaev
- Rutgers, The State University, Piscataway, NJ, 08854, USA
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15
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Buchstein SR, Hinkle DC. Genetic analysis of two bacterial RNA polymerase mutants that inhibit the growth of bacteriophage T7. MOLECULAR & GENERAL GENETICS : MGG 1982; 188:211-8. [PMID: 6759870 DOI: 10.1007/bf00332677] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The Escherichia coli mutants 7009 and BR3 are defective in the growth of bacteriophage T7. We have previously shown that both of these mutant hosts produce an altered RNA polymerase which is resistant to inhibition by the T7 gene 2 protein (De Wyngaert and Hinkle 1979). In both strains, the mutation which prevents T7 growth is closely linked to rifA (rpoB). Both mutants are complemented by transformation with a multicopy plasmid carrying rpoB and rpoC but not by a plasmid carrying only rpoB. This indicates that the mutations reside in rpoC, the structural gene for the beta' subunit of RNA polymerase. When a single copy of the wildtype rpoC allele is introduced into the mutant using the transducing phage lambda drifd18, the mutant allele is dominant over wildtype. The lambda drifd18 transductant also remains unable to support the growth of T7 in the presence of rifampin. This supports our conclusion that the mutation is in rpoC. We have measured the growth of T7 phage, the kinetics of phage DNA synthesis, and the structure of replicative DNA intermediates in several transductants, and compared these results with those obtained in the original mutant strains.
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Shanblatt SH, Nakada D. Escherichia coli mutant which restricts T7 bacteriophage has an altered RNA polymerase. J Virol 1982; 42:1123-6. [PMID: 7047764 PMCID: PMC256954 DOI: 10.1128/jvi.42.3.1123-1126.1982] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
We have previously described an Escherichia coli K-12 mutant, Y49, which restricts the growth of bacteriophage T7 and causes the accumulation of short DNA molecules and head-related particles during infection. We now show that the basis for these effects is the inability of the T7 gene 2 product to inactivate the Y49 RNA polymerase during infection, similar to what has been shown by DeWyngaert and Hinkle (J. Biol. Chem. 254:11247--11253, 1979) for the BR3 and tsnB strains of E. coli.
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Benchimol S, Lucko H, Becker A. A novel endonuclease specified by bacteriophage lambda. Purification and properties of the enzyme. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34657-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Fuchs E, Hirth KP, Henrich B, Kälberer G. Demonstration of the early--late switch in vitro with bacteriophage T7 DNA as template. EUROPEAN JOURNAL OF BIOCHEMISTRY 1980; 113:61-6. [PMID: 7460952 DOI: 10.1111/j.1432-1033.1980.tb06139.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A protein-synthesizing system in vitro, programmed with bacteriophage T7 DNA as template, changed the specificity of gene expression in the course of incubation as a result of newly synthesized T7 early proteins. The system mimics largely the situation in vivo on both the transcriptional and the translational levels, i.e. early gene expression is turned off shortly after late synthesis has been started. These results suggest that the switch from early to late expression does not necessarily require changes in the cellular environment nor is it dependent on the presence of membranes. The main part in this process is played by the phage-dependent RNA polymerase (gene 1 product), whose activity appears 8-10 min after start of incubation. When its activity is reduced by inhibitors or creation of non-optimal conditions, the system is not able to manage the early--late switch.
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West RW, McConnell D, Rodriguez RL. Isolation of E.coli promoters from the late region of bacteriophage T7 DNA. MOLECULAR & GENERAL GENETICS : MGG 1980; 180:439-47. [PMID: 6258028 DOI: 10.1007/bf00425860] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Promotor sequences recognized by Escherichia coli RNA polymerase have been isolated from bacteriophage T7 DNA using the plasmid pBRH4. T7 DNA was digested with the restriction endonuclease Hae III, Alu I, and Eco RI* and the products of these digestions were ligated into the EcoRI site of pBRH4. Cloning of Hae III and Alu I-digested T7 DNA was achieved by blunt-end ligation of these fragments to the polymerized ends of Eco-RI-cleaved pBRH4. This converts blunt-end Eco RI fragments of T7 DNA into cohesive-end EcoRI fragments. Promoter-containing T7 restriction fragments were selected by activation of the tetracycline-resistance gene located on the plasmid vector. The genomic location of each T7 insert was determined and Hpa I-cleaved T7 DNA. Two promoter-active restriction fragments are thought to contain the C and E promoters of T7. However, the majority, of the promoter-active fragments cloned map within the late gene region of T7. In vitro binding studies indicate that E. coli RNA polymerase can form heparin resistant complexes with the cloned T7 DNA promoter fragments. These results suggest that while E. coli RNA polymerase may not participate directly in the transcription of late T7 genes, promoters for this enzyme are present in this region of the DNA.
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21
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Fischer H, Hinkle D. Bacteriophage T7 DNA replication in vitro. Stimulation of DNA synthesis by T7 RNA polymerase. J Biol Chem 1980. [DOI: 10.1016/s0021-9258(19)43926-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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22
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Mooney PQ, North R, Molineux IJ. The role of bacteriophage T7 gene 2 protein in DNA replication. Nucleic Acids Res 1980; 8:3043-53. [PMID: 7001361 PMCID: PMC324143 DOI: 10.1093/nar/8.13.3043] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The in vivo function of the gene 2 protein of bacteriophage T7 has been examined. The gene 2 protein appears to modulate the activity of the gene 3 endonuclease in order to prevent the premature degradation of any newly-formed DNA concatemers. This modulation is not however a direct interacton between the two proteins. In single-burst experiments rifamycin can substitute for the gene 2 protein, allowing formation of fast-sedimenting replicative DNA intermediates and progeny phage production. This suggests that the sole function of the gene 2 protein is inhibition of the host RNA polymerase and that the latter enzyme directs or promotes the endonucleolytic action of the gene 3 protein.
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Saito H, Tabor S, Tamanoi F, Richardson CC. Nucleotide sequence of the primary origin of bacteriophage T7 DNA replication: relationship to adjacent genes and regulatory elements. Proc Natl Acad Sci U S A 1980; 77:3917-21. [PMID: 6254001 PMCID: PMC349738 DOI: 10.1073/pnas.77.7.3917] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The 682-base-pair nucleotide sequence between positions 14.45 and 16.15 on the bacteriophage T7 DNA molecule has been determined. We can identify not only the sequence of the primary origin of DNA replication but also the termination of gene 1, all of genes 1.1 and 1.2, the start of gene 1.3, and a number of regulatory sequences. The endpoints of four deletion mutations that extend into this region have been determined. These mutations are inferred to have arisen by recombination between short homologous sequences, three of which ar T7 RNA polymerase promoters. The base changes of four point mutations in gene 1.2 have been identified. The sequence essential for initiation at the primary origin is located between the left endpoints of the two deletions D2 and D303. Sequence analysis of these mutants assigns the primary origin to a 129-base-pair segment between positions 14.73 and 15.05. This intergenic segment is A+T-rich (75%) and contains a single T7 gene 4 protein recognition site; it is preceded by two tandem T7 RNA polymerase promoters. A model for initiation of T7 DNA replication is presented.
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Abstract
Infection of Escherichia coli with T7 gene 2 mutant phage was abortive; concatemeric phage DNA was synthesized but was not packaged into the phage head, resulting in an accumulation of DNA species shorter in size than the phage genome, concomitant with an accumulation of phage head-related structures. Appearance of concatemeric T7 DNA in gene 2 mutant phage infection during onset of T7 DNA replication indicates that the product of gene 2 was required for proper processing or packaging of concatemer DNA rather than for the synthesis of T7 progeny DNA or concatemer formation. This abortive infection by gene 2 mutant phage could be rescued by rifampin. If rifampin was added at the onset of T7 DNA replication, concatemeric DNA molecules were properly packaged into phage heads, as evidenced by the production of infectious progeny phage. Since the gene 2 product acts as a specific inhibitor of E. coli RNA polymerase by preventing the enzyme from binding T7 DNA, uninhibited E. coli RNA polymerase in gene 2 mutant phage-infected cells interacts with concatemeric T7 DNA and perturbs proper DNA processing unless another inhibitor of the enzyme (rifampin) was added. Therefore, the involvement of gene 2 protein in T7 DNA processing may be due to its single function as the specific inhibitor of the host E. coli RNA polymerase.
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Tamanoi F, Saito H, Richardson CC. Physical mapping of primary and secondary origins of bacteriophage T7 DNA replication. Proc Natl Acad Sci U S A 1980; 77:2656-60. [PMID: 6930658 PMCID: PMC349461 DOI: 10.1073/pnas.77.5.2656] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Deletion mutants of bacteriophage T7 have been used to identify and to map, by electron microscopy, the origins of T7 DNA replication. The primary origin of phage T7 DNA replication lies within a 100-base-pair region located 14.75-15.0% of the distance from the genetic left end of the DNA molecule. T7 phage whose DNA contains a deletion of this region initiate replication at secondary origins, the predominant one of which is located at a distance approximately 4% from the left end of the molecule.
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DeWyngaert MA, Hinkle DC. Characterization of the defects in bacteriophage T7 DNA synthesis during growth in the Escherichia coli mutant tsnB. J Virol 1980; 33:780-8. [PMID: 6997508 PMCID: PMC288604 DOI: 10.1128/jvi.33.2.780-788.1980] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The Escherichia coli mutant tsnB (M. Chamberlin, J. Virol. 14:509-516, 1974) is unable to support the growth of bacteriophage T7, although all classes of phage proteins are produced and the host is killed by the infection. During growth in this mutant host, the rate of phage DNA synthesis is reduced and the DNA is not packaged into stable, phagelike particles. The replicating DNA forms concatemers but the very large replicative intermediates (approximately 440S) identified by Paetkau et al. (J. Virol. 22:130-141, 1977) are not detected in T7+-infected tsnB cells. These large structures are formed in tsnB cells infected with a T7 gene 3 (endonuclease) mutant, where normal processing of the large intermediates into shorter concatemers is blocked. At later times during infection of tsnB cells, the replicating DNA accumulates in molecules about 30% shorter than unit length. Analysis of this DNA with a restriction endonuclease indicates that it is missing sequences from the ends (particularly the left end) of the genome. The loss of these specific sequences does not occur during infections with T7 gene 10 (head protein) or gene 19 (maturation protein) mutants. This suggests that the processing of concatemers into unit-length DNA molecules may occur normally in T7 -infected tsnB cells and that the shortened DNA arises from exonucleolytic degradation of the mature DNA molecules. These results are discussed in relation to our recent observation (M. A. DeWyngaert and D. C. Hinkle, J. Biol. Chem. 254:11247-11253, 1979) that E. coli tsnB produces an altered RNA polymerase which is resistance to inhibition by the T7 gene 2 protein.
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