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Vaquero-Sedas MI, Vega-Palas MA. A Nested PCR Telomere Fusion Assay Highlights the Widespread End-Capping Protection of Arabidopsis CTC1. Int J Mol Sci 2024; 25:672. [PMID: 38203842 PMCID: PMC10779545 DOI: 10.3390/ijms25010672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Revised: 11/15/2023] [Accepted: 11/18/2023] [Indexed: 01/12/2024] Open
Abstract
Telomeres protect the ends of linear eukaryotic chromosomes from being recognized as DNA double-strand breaks. Two major protein complexes are involved in the protection of telomeres: shelterin and CST. The dysfunction of these complexes can challenge the function of telomeres and lead to telomere fusions, breakage-fusion-bridge cycles, and cell death. Therefore, monitoring telomere fusions helps to understand telomeres biology. Telomere fusions are often analyzed by Fluorescent In Situ Hybridization (FISH) or PCR. Usually, both methods involve hybridization with a telomeric probe, which allows the detection of fusions containing telomeric sequences, but not of those lacking them. With the aim of detecting both types of fusion events, we have developed a nested PCR method to analyze telomere fusions in Arabidopsis thaliana. This method is simple, accurate, and does not require hybridization. We have used it to analyze telomere fusions in wild-type and mutant plants altered in CTC1, one of the three components of the Arabidopsis CST telomere capping complex. Our results show that null ctc1-2 mutant plants display fusions between all telomeric regions present in Arabidopsis chromosomes 1, 3 and 5, thus highlighting the widespread end-capping protection achieved by CTC1.
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Affiliation(s)
| | - Miguel A. Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), E41092 Seville, Spain;
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2
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Abstract
The epigenetic features of defined chromosomal domains condition their biochemical and functional properties. Therefore, there is considerable interest in studying the epigenetic marks present at relevant chromosomal loci. Telomeric regions, which include telomeres and subtelomeres, have been traditionally considered heterochromatic. However, whereas the heterochromatic nature of subtelomeres has been widely accepted, the epigenetic status of telomeres remains controversial. Here, we studied the epigenetic features of Arabidopsis (Arabidopsis thaliana) telomeres by analyzing multiple genome-wide ChIP-seq experiments. Our analyses revealed that Arabidopsis telomeres are not significantly enriched either in euchromatic marks like H3K4me2, H3K9ac, and H3K27me3 or in heterochromatic marks such as H3K27me1 and H3K9me2. Thus, telomeric regions in Arabidopsis have a bimodal chromatin organization with telomeres lacking significant levels of canonical euchromatic and heterochromatic marks followed by heterochromatic subtelomeres. Since heterochromatin is known to influence telomere function, the heterochromatic modifications present at Arabidopsis subtelomeres could play a relevant role in telomere biology.
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Affiliation(s)
- María I Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), Seville E41092, Spain
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3
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Farrell C, Vaquero-Sedas MI, Cubiles MD, Thompson M, Vega-Vaquero A, Pellegrini M, Vega-Palas MA. A complex network of interactions governs DNA methylation at telomeric regions. Nucleic Acids Res 2022; 50:1449-1464. [PMID: 35061900 PMCID: PMC8860613 DOI: 10.1093/nar/gkac012] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 01/10/2022] [Indexed: 12/13/2022] Open
Abstract
DNA methylation modulates telomere function. In Arabidopsis thaliana, telomeric regions have a bimodal chromatin organization with unmethylated telomeres and methylated subtelomeres. To gain insight into this organization we have generated TAIR10-Tel, a modified version of the Arabidopsis reference genome with additional sequences at most chromosome ends. TAIR10-Tel has allowed us to analyse DNA methylation at nucleotide resolution level in telomeric regions. We have analysed the wild-type strain and mutants that encode inactive versions of all currently known relevant methyltransferases involved in cytosine methylation. These analyses have revealed that subtelomeric DNA methylation extends 1 to 2 kbp from Interstitial Telomeric Sequences (ITSs) that abut or are very near to telomeres. However, DNA methylation drops at the telomeric side of the telomere-subtelomere boundaries and disappears at the inner part of telomeres. We present a comprehensive and integrative model for subtelomeric DNA methylation that should help to decipher the mechanisms that govern the epigenetic regulation of telomeres. This model involves a complex network of interactions between methyltransferases and subtelomeric DNA sequences.
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Affiliation(s)
- Colin Farrell
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, CA90095, USA
| | - María I Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), Seville, E41092, Spain
| | - María D Cubiles
- Departamento de Estadística e Investigación Operativa, Facultad de Matemáticas, Universidad de Sevilla, Seville, E41012, Spain
| | - Michael Thompson
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, CA90095, USA
| | - Alejandro Vega-Vaquero
- Escuela Técnica Superior de Ingeniería Informática, Universidad de Sevilla, Seville, E41012, Spain
| | - Matteo Pellegrini
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, CA90095, USA.,Institute of Genomics and Proteomics, Los Angeles, CA90095, USA
| | - Miguel A Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), Seville, E41092, Spain
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4
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Abstract
The epigenetic modifications of human telomeres play a relevant role in telomere functions and cell proliferation. Therefore, their study is becoming an issue of major interest. These epigenetic modifications are usually analyzed by microscopy or by chromatin immunoprecipitation (ChIP). However, these analyses could be challenged by subtelomeres and/or interstitial telomeric sequences (ITSs). Whereas telomeres and subtelomeres cannot be differentiated by microscopy techniques, telomeres and ITSs might not be differentiated in ChIP analyses. In addition, ChIP analyses of telomeres should be properly controlled. Hence, studies focusing on the epigenetic features of human telomeres have to be carefully designed and interpreted. Here, we present a comprehensive discussion on how subtelomeres and ITSs might influence studies of human telomere epigenetics. We specially focus on the influence of ITSs and some experimental aspects of the ChIP technique on ChIP analyses. In addition, we propose a specific pipeline to accurately perform these studies. This pipeline is very simple and can be applied to a wide variety of cells, including cancer cells. Since the epigenetic status of telomeres could influence cancer cells proliferation, this pipeline might help design precise epigenetic treatments for specific cancer types.
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Affiliation(s)
- María I Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, 41092 Seville, Spain.
| | - Miguel A Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, 41092 Seville, Spain.
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5
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Cubiles MD, Barroso S, Vaquero-Sedas MI, Enguix A, Aguilera A, Vega-Palas MA. Epigenetic features of human telomeres. Nucleic Acids Res 2019; 46:2347-2355. [PMID: 29361030 PMCID: PMC5861411 DOI: 10.1093/nar/gky006] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Accepted: 01/09/2018] [Indexed: 01/02/2023] Open
Abstract
Although subtelomeric regions in humans are heterochromatic, the epigenetic nature of human telomeres remains controversial. This controversy might have been influenced by the confounding effect of subtelomeric regions and interstitial telomeric sequences (ITSs) on telomeric chromatin structure analyses. In addition, different human cell lines might carry diverse epigenetic marks at telomeres. We have developed a reliable procedure to study the chromatin structure of human telomeres independently of subtelomeres and ITSs. This procedure is based on the statistical analysis of multiple ChIP-seq experiments. We have found that human telomeres are not enriched in the heterochromatic H3K9me3 mark in most of the common laboratory cell lines, including embryonic stem cells. Instead, they are labeled with H4K20me1 and H3K27ac, which might be established by p300. These results together with previously published data argue that subtelomeric heterochromatin might control human telomere functions. Interestingly, U2OS cells that exhibit alternative lengthening of telomeres have heterochromatic levels of H3K9me3 in their telomeres.
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Affiliation(s)
- María D Cubiles
- Departamento de Estadística e Investigación Operativa, Facultad de Matemáticas, Universidad de Sevilla, 41012 Seville, Spain
| | - Sonia Barroso
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Avd. Américo Vespucio s/n, 41092 Seville, Spain
| | - María I Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), Avd. Américo Vespucio n° 49, 41092 Seville, Spain
| | - Alicia Enguix
- Departamento de Estadística e Investigación Operativa, Facultad de Matemáticas, Universidad de Sevilla, 41012 Seville, Spain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Avd. Américo Vespucio s/n, 41092 Seville, Spain
| | - Miguel A Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), Avd. Américo Vespucio n° 49, 41092 Seville, Spain
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6
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Vega-Vaquero A, Bonora G, Morselli M, Vaquero-Sedas MI, Rubbi L, Pellegrini M, Vega-Palas MA. Novel features of telomere biology revealed by the absence of telomeric DNA methylation. Genome Res 2016; 26:1047-56. [PMID: 27405804 PMCID: PMC4971770 DOI: 10.1101/gr.202465.115] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Accepted: 06/20/2016] [Indexed: 12/21/2022]
Abstract
Cytosine methylation regulates the length and stability of telomeres, which can affect a wide variety of biological features, including cell differentiation, development, or illness. Although it is well established that subtelomeric regions are methylated, the presence of methylated cytosines at telomeres has remained controversial. Here, we have analyzed multiple bisulfite sequencing studies to address the methylation status of Arabidopsis thaliana telomeres. We found that the levels of estimated telomeric DNA methylation varied among studies. Interestingly, we estimated higher levels of telomeric DNA methylation in studies that produced C-rich telomeric strands with lower efficiency. However, these high methylation estimates arose due to experimental limitations of the bisulfite technique. We found a similar phenomenon for mitochondrial DNA: The levels of mitochondrial DNA methylation detected were higher in experiments with lower mitochondrial read production efficiencies. Based on experiments with high telomeric C-rich strand production efficiencies, we concluded that Arabidopsis telomeres are not methylated, which was confirmed by methylation-dependent restriction enzyme analyses. Thus, our studies indicate that telomeres are refractory to de novo DNA methylation by the RNA-directed DNA methylation machinery. This result, together with previously reported data, reveals that subtelomeric DNA methylation controls the homeostasis of telomere length.
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Affiliation(s)
- Alejandro Vega-Vaquero
- Technical Superior School of Informatics Engineering, University of Seville, 41080 Seville, Spain
| | - Giancarlo Bonora
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, California 90095, USA
| | - Marco Morselli
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, California 90095, USA
| | - María I Vaquero-Sedas
- Institute of Vegetal Biochemistry and Photosynthesis, CSIC-University of Seville, IBVF (CSIC-US), 41092 Seville, Spain
| | - Liudmilla Rubbi
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, California 90095, USA
| | - Matteo Pellegrini
- Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, California 90095, USA
| | - Miguel A Vega-Palas
- Institute of Vegetal Biochemistry and Photosynthesis, CSIC-University of Seville, IBVF (CSIC-US), 41092 Seville, Spain
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7
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Abstract
In humans, telomere length studies have acquired great relevance because the length of telomeres has been related to natural processes like disease, aging and cancer. However, very little is known about the influence of telomere length on the biology of wild type plants. The length of plant telomeres has been usually studied by Terminal Restriction Fragment (TRF) analyses. This technique requires high amounts of tissue, including multiple cell types, which might be the reason why very little is known about the influence of telomere length on plant natural processes. In contrast, many of the human telomere length studies have focused on homogenous cell populations. Most of these studies have been performed by PCR, using telomeric degenerated primers, which allow the determination of telomere length from small amounts of human cells. Here, we have adapted the human PCR procedure to analyze the length of Arabidopsis thaliana telomeres. This PCR approach will facilitate the analysis of telomere length from low amounts of tissue. We have used it to determine that CG and non CG DNA methylation positively regulates Arabidopsis telomere length.
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Affiliation(s)
- María I. Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), c/Américo Vespucio n° 49, 41092 Seville, Spain
| | - Miguel A. Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), c/Américo Vespucio n° 49, 41092 Seville, Spain
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8
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Vaquero-Sedas MI, Vega-Palas MA. Differential association of Arabidopsis telomeres and centromeres with histone H3 variants. Sci Rep 2013; 3:1202. [PMID: 23383372 PMCID: PMC3563029 DOI: 10.1038/srep01202] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Accepted: 01/11/2013] [Indexed: 01/25/2023] Open
Abstract
Two different groups, using ChIP-seq data, have recently published the genome-wide distribution of histones H3.1 and H3.3 in Arabidopsis thaliana. In one report, Stroud and colleagues determined that, whereas H3.1 was enriched in repetitive pericentromeric and silent chromatin, H3.3 was enriched in transcriptionally active regions. This work was performed using seedlings, which contained dividing and non-dividing cells. In a second report, Wollmann and colleagues found similar results analyzing dividing or non-dividing tissue. None of these reports addressed the analysis of telomeres or centromeres. Our group has recently described an experimental approach that allows the study of the epigenetic status of some Arabidopsis repetitive sequences by analyzing ChIP-seq data. By using this approach and the data generated by Stroud, Wollmann and colleagues, we found that telomeres are enriched in H3.3 with regard to the centromeric 178 bp repeats, whereas the centromeric repeats are enriched in H3.1 with regard to telomeres.
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Affiliation(s)
- María I Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-US), c/Américo Vespucio n° 49, 41092 Seville, Spain
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9
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Vaquero-Sedas MI, Vega-Palas MA. Human Long Telomeres and Epigenetic Marks. Cell 2013. [DOI: 10.4236/cellbio.2013.22009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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10
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Vaquero-Sedas MI, Luo C, Vega-Palas MA. Analysis of the epigenetic status of telomeres by using ChIP-seq data. Nucleic Acids Res 2012; 40:e163. [PMID: 22855559 PMCID: PMC3505975 DOI: 10.1093/nar/gks730] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Accepted: 07/06/2012] [Indexed: 01/17/2023] Open
Abstract
The chromatin structure of eukaryotic telomeres plays an essential role in telomere functions. However, their study might be impaired by the presence of interstitial telomeric sequences (ITSs), which have a widespread distribution in different model systems. We have developed a simple approach to study the chromatin structure of Arabidopsis telomeres independently of ITSs by analyzing ChIP-seq data. This approach could be used to study the chromatin structure of telomeres in some other eukaryotes. The analysis of ChIP-seq experiments revealed that Arabidopsis telomeres have higher density of histone H3 than centromeres, which might reflects their short nucleosomal organization. These experiments also revealed that Arabidopsis telomeres have lower levels of heterochromatic marks than centromeres (H3K9(Me2) and H3K27(Me)), higher levels of some euchromatic marks (H3K4(Me2) and H3K9Ac) and similar or lower levels of other euchromatic marks (H3K4(Me3), H3K36(Me2), H3K36(Me3) and H3K18Ac). Interestingly, the ChIP-seq experiments also revealed that Arabidopsis telomeres exhibit high levels of H3K27(Me3), a repressive mark that associates with many euchromatic genes. The epigenetic profile of Arabidopsis telomeres is closely related to the previously defined chromatin state 2. This chromatin state is found in 23% of Arabidopsis genes, many of which are repressed or lowly expressed. At least, in part, this scenario is similar in rice.
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Affiliation(s)
- María I. Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-USE), c/ Américo Vespucio n° 49, 41092 Seville, Spain and Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ, USA
| | - Chongyuan Luo
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-USE), c/ Américo Vespucio n° 49, 41092 Seville, Spain and Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ, USA
| | - Miguel A. Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, IBVF (CSIC-USE), c/ Américo Vespucio n° 49, 41092 Seville, Spain and Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ, USA
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11
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Vaquero-Sedas MI, Vega-Palas MA. DNA methylation at tobacco telomeric sequences. Plant Mol Biol 2011; 77:529-31; author reply 533-6. [PMID: 22016003 DOI: 10.1007/s11103-011-9833-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Accepted: 10/06/2011] [Indexed: 05/31/2023]
Abstract
Majerová et al. (Plant Mol Biol, 2011) have recently reported that a considerable fraction of cytosines at tobacco telomeres is methylated. Although the data presented in this report indicate that tobacco telomeric sequences undergo certain levels of DNA methylation, it is not clear whether the methylated sequences are at telomeres, at internal chromosomal loci or at both.
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12
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Abstract
Telomeres prevent chromosome fusions and degradation by exonucleases and are implicated in DNA repair, homologous recombination, chromosome pairing and segregation. All these functions of telomeres require the integrity of their chromatin structure, which has been traditionally considered as heterochromatic. In agreement with this idea, different studies have reported that telomeres associate with heterochromatic marks. However, these studies addressed simultaneously the chromatin structures of telomeres and subtelomeric regions or the chromatin structure of telomeres and Interstitial Telomeric Sequences (ITSs). The independent analysis of Arabidopsis telomeres, subtelomeric regions and ITSs has allowed the discovery of euchromatic telomeres. In Arabidopsis, whereas subtelomeric regions and ITSs associate with heterochromatic marks, telomeres exhibit euchromatic features. We think that this scenario could be found in other model systems if the chromatin organizations of telomeres, subtelomeric regions and ITSs are independently analyzed.
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Affiliation(s)
- María I Vaquero-Sedas
- Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Seville, Spain
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13
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Vaquero-Sedas MI, Gámez-Arjona FM, Vega-Palas MA. Arabidopsis thaliana telomeres exhibit euchromatic features. Nucleic Acids Res 2011; 39:2007-17. [PMID: 21071395 PMCID: PMC3064777 DOI: 10.1093/nar/gkq1119] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2010] [Revised: 10/19/2010] [Accepted: 10/19/2010] [Indexed: 12/03/2022] Open
Abstract
Telomere function is influenced by chromatin structure and organization, which usually involves epigenetic modifications. We describe here the chromatin structure of Arabidopsis thaliana telomeres. Based on the study of six different epigenetic marks we show that Arabidopsis telomeres exhibit euchromatic features. In contrast, subtelomeric regions and telomeric sequences present at interstitial chromosomal loci are heterochromatic. Histone methyltransferases and the chromatin remodeling protein DDM1 control subtelomeric heterochromatin formation. Whereas histone methyltransferases are required for histone H3K9(2Me) and non-CpG DNA methylation, DDM1 directs CpG methylation but not H3K9(2Me) or non-CpG methylation. These results argue that both kinds of proteins participate in different pathways to reinforce subtelomeric heterochromatin formation.
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Affiliation(s)
| | | | - Miguel A. Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla – CSIC, c/ Américo Vespucio n° 49, 41092 Seville, Spain
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14
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Gámez-Arjona FM, López-López C, Vaquero-Sedas MI, Vega-Palas MA. On the organization of the nucleosomes associated with telomeric sequences. Biochim Biophys Acta 2010; 1803:1058-61. [PMID: 20381544 DOI: 10.1016/j.bbamcr.2010.03.021] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2010] [Revised: 03/29/2010] [Accepted: 03/29/2010] [Indexed: 11/25/2022]
Abstract
The functions of telomeres and, probably, of interstitial telomeric sequences (ITSs) are influenced by their chromatin structure and organization. Telomeres in higher eukaryotes fold into nucleosomes that are about 20-40 bp shorter than the nucleosomes associated with bulk chromatin. Although the functional relevance of this short nucleosomal organization remains unknown, it is believed that short nucleosomes should contribute to telomere function. Whereas telomeric nucleosomes have been widely studied in different organisms, very little is known about the nucleosomal organization of ITSs. Chinese hamster ITSs have been found to associate with short nucleosomes. However, we have found that Arabidopsis thaliana ITSs fold into nucleosomes that have a repeat length similar to bulk chromatin. We discuss how the primary sequence of telomeres and ITSs could influence their nucleosomal organization.
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Affiliation(s)
- Francisco M Gámez-Arjona
- Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla and CSIC, Américo Vespucio 49, E-41092 Seville, Spain
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15
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Schober H, Kalck V, Vega-Palas MA, Van Houwe G, Sage D, Unser M, Gartenberg MR, Gasser SM. Controlled exchange of chromosomal arms reveals principles driving telomere interactions in yeast. Genome Res 2007; 18:261-71. [PMID: 18096749 DOI: 10.1101/gr.6687808] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The 32 telomeres in the budding yeast genome cluster in three to seven perinuclear foci. Although individual telomeres and telomeric foci are in constant motion, preferential juxtaposition of some telomeres has been scored. To examine the principles that guide such long-range interactions, we differentially tagged pairs of chromosome ends and developed an automated three-dimensional measuring tool that determines distances between two telomeres. In yeast, all chromosomal ends terminate in TG(1-3) and middle repetitive elements, yet subgroups of telomeres also share extensive homology in subtelomeric coding domains. We find that up to 21 kb of >90% sequence identity does not promote telomere pairing in interphase cells. To test whether unique sequence elements, arm length, or chromosome territories influence juxtaposition, we reciprocally swapped terminal domains or entire chromosomal arms from one chromosome to another. We find that the distal 10 kb of Tel6R promotes interaction with Tel6L, yet only when the two telomeres are present on the same chromosome. By manipulating the length and sequence composition of the right arm of chr 5, we confirm that contact between telomeres on opposite chromatid arms of equal length is favored. These results can be explained by the polarized Rabl arrangement of yeast centromeres and telomeres, which promote to telomere pairing by allowing contact between chromosome arms of equal length in anaphase.
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Affiliation(s)
- Heiko Schober
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland
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16
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Luo K, Vega-Palas MA, Grunstein M. Rap1-Sir4 binding independent of other Sir, yKu, or histone interactions initiates the assembly of telomeric heterochromatin in yeast. Genes Dev 2002; 16:1528-39. [PMID: 12080091 PMCID: PMC186350 DOI: 10.1101/gad.988802] [Citation(s) in RCA: 182] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2002] [Accepted: 05/03/2002] [Indexed: 11/24/2022]
Abstract
In Saccharomyces cerevisiae, heterochromatin-like regions are found near telomeres and at the silent mating-type loci, where they can repress genes in an epigenetic manner. Several proteins are involved in telomeric heterochromatin structure including Rap1, Sir2, Sir3, Sir4, yKu70 (Hdf1), yKu80 (Hdf2), and the N termini of histones H3 and H4. By recognizing cis-acting DNA-binding sites, Rap1 is believed to recruit Sir and other silencing proteins and determine where heterochromatin forms. The integrity of heterochromatin also requires the binding of Sir proteins to histones that may form a scaffold for Sir protein interactions with chromatin. In this study we describe how the heterochromatin complex may form initially and how it differs from the complex that spreads along the chromosome. We found that close to the telomere end, Sir4 can bind Rap1 independently of Sir2, Sir3, yKu70/yKu80, and the intact H4 N terminus. In contrast, Sir4 binding requires all of the silencing factors further along telomeric heterochromatin. These data indicate that Sir4 binding to Rap1 initiates the sequential association of Sir and other proteins, allowing the subsequent spreading of the heterochromatin proteins along the chromosome.
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Affiliation(s)
- Kunheng Luo
- Department of Biological Chemistry, UCLA School of Medicine, 90095, USA
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17
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Madueño F, Vega-Palas MA, Flores E, Herrero A. A cytoplasmic-membrane protein repressible by ammonium inSynechococcusR2: altered expression in nitrate-assimilation mutants. FEBS Lett 2001. [DOI: 10.1016/0014-5793(88)80936-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Tous C, Vega-Palas MA, Vioque A. Conditional expression of RNase P in the cyanobacterium Synechocystis sp. PCC6803 allows detection of precursor RNAs. Insight in the in vivo maturation pathway of transfer and other stable RNAs. J Biol Chem 2001; 276:29059-66. [PMID: 11384989 DOI: 10.1074/jbc.m103418200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have constructed a strain (CT1) that expresses RNase P conditionally with the aim to analyze the in vivo tRNA processing pathway and the biological role that RNase P plays in Synechocystis 6803. In this strain, the rnpB gene, coding for the RNA subunit of RNase P, has been placed under the control of the petJ gene promoter (P(petJ)), which is repressed by copper, cell growth, and accumulation of RNase P RNA is inhibited in CT1 after the addition of copper, indicating that the regulation by copper is maintained in the chimerical P(petJ)-rnpB gene and that RNase P is essential for growth in Synechocystis. We have analyzed several RNAs by Northern blot and primer extension in CT1. Upon addition of copper to the culture medium, precursors of the mature tRNAs are detected. Furthermore, our results indicate that there is a preferred order in the action of RNase P when it processes a dimeric tRNA precursor. The precursors detected are 3'-processed, indicating that 3' processing can occur before 5' processing by RNase P. The size of the precursors suggests that the terminal CCA sequence is already present before RNase P processing. We have also analyzed other potential RNase P substrates, such as the precursors of tmRNA and 4.5 S RNA. In both cases, accumulation of larger than mature size RNAs is observed after transferring the cells to a copper-containing medium.
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MESH Headings
- Base Sequence
- Cell Division
- Chromosome Mapping
- Copper/pharmacology
- Cyanobacteria/cytology
- Cyanobacteria/enzymology
- Cyanobacteria/genetics
- Endoribonucleases/genetics
- Endoribonucleases/metabolism
- Gene Expression Regulation, Bacterial/drug effects
- Gene Expression Regulation, Enzymologic/drug effects
- Genes, Fungal
- Kinetics
- Molecular Sequence Data
- Promoter Regions, Genetic
- RNA Precursors/genetics
- RNA Precursors/metabolism
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Catalytic/genetics
- RNA, Catalytic/metabolism
- RNA, Transfer, Thr/genetics
- RNA, Transfer, Tyr/genetics
- Ribonuclease P
- Sequence Alignment
- Sequence Homology, Nucleic Acid
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Affiliation(s)
- C Tous
- Instituto de Bioquimica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, c/Americo Vespucio s/n, 41092 Sevilla, Spain
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Abstract
The heterochromatin at telomeres can repress the expression of reporter genes when they are transplanted into their vicinity. Although this transcriptional silencing has been widely characterized using reporter genes, the ability of telomeres to repress natural subtelomeric genes has remained uncertain. In a previous report we described telomeric silencing of a yeast retrotransposon. Here we describe the identification of a subtelomeric gene from Saccharomyces cerevisiae that is subject to natural telomeric silencing. In addition, we show that telomeric silencing is not a general feature of the first ORFs located adjacent to Telomere-Associated Sequences.
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Affiliation(s)
- M A Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Isla de la Cartuja, Sevilla, Spain.
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Venditti S, Vega-Palas MA, Di Stefano G, Di Mauro E. Imbalance in dosage of the genes for the heterochromatin components Sir3p and histone H4 results in changes in the length and sequence organization of yeast telomeres. Mol Gen Genet 1999; 262:367-77. [PMID: 10517334 DOI: 10.1007/s004380051095] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Telomeric heterochromatin plays an essential role in telomere function, including the regulation of telomere length. We observe that in Saccharomyces cerevisiae an imbalance in the dosage of genes for two protein components of heterochromatin (namely Sir3p and histone H4) causes modifications in telomere length and telomere sequence organization. The effects of Sir3p/H4 imbalance were analyzed in yeast strains in which the wild-type SIR3 gene (normally a single-copy gene) was either absent or present in 20-30 copies, and both histone H4 genes (HHF1 and HHF2) were present or HHF1 was deleted, thus covering a wide range of viable gene-dosage combinations. Modifications of telomeres and of subtelomeric regions were identified by analyzing both the overall telomere population and by focusing on two single telomeric regions: the left telomere of chromosome III (LIII) and the right telomere of chromosome XI (RXI). The modifications induced by alteration of the Sir3p/H4 ratio consist of a reduction in the length and an increase in the instability of the terminal block of (C(1-3)A)n repeats and in susceptibility to insertion of Y' elements into this repeat element. Restoration of the wild-type gene ratio (by removal of the extra copies of SIR3 or by complementation with the missing second copy of HHF) restored the original telomere organization, both with respect to the length of the (C(1-3)A)n repeat stretch and the absence of Y' elements. This behavior shows that the stability of the wild-type sequence organization requires maintenance of the normal structure of telomeric heterochromatin.
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Affiliation(s)
- S Venditti
- Fondazione Istituto Pasteur-Fondazione Cenci-Bolognetti, Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, Rome, Italy
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Venditti S, Vega-Palas MA, Di Mauro E. Heterochromatin organization of a natural yeast telomere. Recruitment of Sir3p through interaction with histone H4 N terminus is required for the establishment of repressive structures. J Biol Chem 1999; 274:1928-33. [PMID: 9890947 DOI: 10.1074/jbc.274.4.1928] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The chromatin organization of eukaryotic telomeres is essential for telomeric function and is currently receiving great attention. In yeast, the structural organization of telomeres involves a complex interplay of telomeric proteins that results in the formation of heterochromatin. This telomeric heterochromatin involves homotypic and heterotypic protein interactions that have been summarized in a general model. Recent analyses have focused on the study of the structural complexity at yeast telomeres to the level of specific nucleosomes and of the distribution of protein complexes in a natural telomeric region (LIII). In this report, we further analyze the structural complexity of LIII and the implication of this structure on telomeric silencing. It is shown that the establishment of repressive heterochromatin structures at LIII requires the recruitment of Sir3p through interaction with the N terminus of histone H4. The establishment of such structures does not require acetylation of any of four lysines located in the H4 N terminus (lysines 5, 8, 12, and 16).
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Affiliation(s)
- S Venditti
- Fondazione "Istituto Pasteur-Fondazione Cenci-Bolognetti", c/o Dipartimento di Genetica e Biologia Molecolare Università "La Sapienza", P. le A. Moro 5, 00185-Roma Italy
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22
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Vega-Palas MA, Venditti S, Di Mauro E. Heterochromatin organization of a natural yeast telomere. Changes of nucleosome distribution driven by the absence of Sir3p. J Biol Chem 1998; 273:9388-92. [PMID: 9545262 DOI: 10.1074/jbc.273.16.9388] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have defined the in vivo heterochromatin structure of the left telomere of Saccharomyces cerevisiae chromosome III (LIII). Analysis of heterochromatin of a single telomere was so far lacking, due to the difficulties intrinsic to the highly repetitive nature of telomeric sequences. In LIII, the terminal (C1-3A)n repetitive sequences are followed by a complete X element and by the single copy Ty5-1 retrotransposon. Both the telosome and the X element exhibit overall resistance to micrococcal nuclease digestion reflecting their tight chromatin structure organization. The X element contains protein complexes and irregularly distributed but well localized nucleosomes. In contrast, a regular array of phased nucleosomes is associated with the promoter region of Ty5-1 and with the more centromere-proximal sequences. The lack of a structural component of yeast telomeres, the SIR3 protein, does not alter the overall tight organization of the X element but causes a nucleosome rearrangement within the promoter region of Ty5-1 and releases Ty5-1 silencing. Thus, Sir3p links the modification of the heterochromatin structure with loss of transcriptional silencing.
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Affiliation(s)
- M A Vega-Palas
- Fondazione Istituto Pasteur-Fondazione Cenci-Bolognetti, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, P.le Aldo Moro 5, 00185 Roma, Italy
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Abstract
The alcohol dehydrogenase (Adh) gene from Arabidopsis shows enhanced sensitivity to DNase I in cells that express the gene. This generalized sensitivity to DNase I is demarcated by position -500 on the 5' side and the end of the mRNA on the 3' side. Thus, the gene defined as the promoter and mRNA coding region corresponds very closely in size with the gene defined as a nuclease-sensitive domain. This is a remarkably close correspondence between a sensitive domain and a eukaryotic transcriptional unit, because previously reported DNase I-sensitive domains include large regions of DNA that are not transcribed. Nucleosomes are present in the coding region of the Adh gene when it is expressed, indicating that the transcriptional elongation process causes nucleosome disruption rather than release of nucleosomes from the coding region. In addition, the regulatory region contains a loosely positioned nucleosome that is separated from adjacent nucleosomes by internucleosomic DNA segments longer than the average linker DNA in bulk chromatin. This specific array of nucleosomes coexists with bound transcription factors that could contribute to the organization of the nucleosome arrangement. These results enhance our understanding of the complex interactions among DNA, nucleosomes, and transcription factors during gene expression in plants.
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Affiliation(s)
- M A Vega-Palas
- Horticultural Sciences Department, University of Florida, Gainesville 32611, USA
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Vega-Palas MA, Flores E, Herrero A. NtcA, a global nitrogen regulator from the cyanobacterium Synechococcus that belongs to the Crp family of bacterial regulators. Mol Microbiol 1992; 6:1853-9. [PMID: 1630321 DOI: 10.1111/j.1365-2958.1992.tb01357.x] [Citation(s) in RCA: 152] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The gene ntcA is required for full expression of proteins subject to ammonium repression in the cyanobacterium Synechococcus. A 3.1 kb DNA fragment able to complement an ntcA mutant was digested with exonuclease III, and deleted fragments of different size were tested for complementation of that mutant, allowing the localization of its mutation within a BamHI-HindIII genomic fragment of c. 0.4 kb. Insertion of a chloramphenicol-resistance-encoding gene cassette into both the BamHI and the HindIII sites of wild-type Synechococcus resulted in a pleiotropic, nitrogen-assimilation-minus phenotype, corroborating the presence of the ntcA gene in that genomic region. Sequencing of DNA in this region showed the presence of an open reading frame that included both the BamHI and the HindIII sites. The ntcA gene product, NtcA, is a protein of 24817 Da which belongs to a family of bacterial transcriptional activators that, among others, includes Crp and Fnr from Escherichia coli. Of special biological significance, it appears, is the presence of a conserved helix-turn-helix motif in the sequence close to the C-terminal end of all the proteins in the family. The gene ntcA is proposed to encode a transcriptional activator of genes subject to nitrogen control in Synechococcus.
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Affiliation(s)
- M A Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla y CSIC, Facultad de Biología, Spain
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Vega-Palas MA, Madueño F, Herrero A, Flores E. Identification and cloning of a regulatory gene for nitrogen assimilation in the cyanobacterium Synechococcus sp. strain PCC 7942. J Bacteriol 1990; 172:643-7. [PMID: 1967601 PMCID: PMC208487 DOI: 10.1128/jb.172.2.643-647.1990] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Twenty-seven mutants that were unable to assimilate nitrate were isolated from Synechococcus sp. strain PCC 7942. In addition to mutants that lacked nitrate reductase or nitrite reductase, seven pleiotropic mutants impaired in both reductases, glutamine synthetase, and methylammonium transport were also isolated. One of the pleiotropic mutants was complemented by transformation with a cosmid gene bank from wild-type strain PCC 7942. Three complementing cosmids were isolated, and a 3.1-kilobase-pair DNA fragment that was still able to complement the mutant was identified. The regulatory gene that was cloned (ntcA) appeared to be required for full expression of proteins subject to ammonium repression in Synechococcus sp.
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Affiliation(s)
- M A Vega-Palas
- Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-Consejo Superior de Investigaciones Cientificas, Spain
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