1
|
Miyoshi K, Tatsumoto Y, Ozaki S, Katayama T. Negative feedback for DARS2-Fis complex by ATP-DnaA supports the cell cycle-coordinated regulation for chromosome replication. Nucleic Acids Res 2021; 49:12820-12835. [PMID: 34871419 PMCID: PMC8682772 DOI: 10.1093/nar/gkab1171] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 11/05/2021] [Accepted: 11/11/2021] [Indexed: 11/13/2022] Open
Abstract
In Escherichia coli, the replication initiator DnaA oscillates between an ATP- and an ADP-bound state in a cell cycle-dependent manner, supporting regulation for chromosome replication. ATP-DnaA cooperatively assembles on the replication origin using clusters of low-affinity DnaA-binding sites. After initiation, DnaA-bound ATP is hydrolyzed, producing initiation-inactive ADP-DnaA. For the next round of initiation, ADP-DnaA binds to the chromosomal locus DARS2, which promotes the release of ADP, yielding the apo-DnaA to regain the initiation activity through ATP binding. This DnaA reactivation by DARS2 depends on site-specific binding of IHF (integration host factor) and Fis proteins and IHF binding to DARS2 occurs specifically during pre-initiation. Here, we reveal that Fis binds to an essential region in DARS2 specifically during pre-initiation. Further analyses demonstrate that ATP-DnaA, but not ADP-DnaA, oligomerizes on a cluster of low-affinity DnaA-binding sites overlapping the Fis-binding region, which competitively inhibits Fis binding and hence the DARS2 activity. DiaA (DnaA initiator-associating protein) stimulating ATP-DnaA assembly enhances the dissociation of Fis. These observations lead to a negative feedback model where the activity of DARS2 is repressed around the time of initiation by the elevated ATP-DnaA level and is stimulated following initiation when the ATP-DnaA level is reduced.
Collapse
Affiliation(s)
- Kenya Miyoshi
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
| | - Yuka Tatsumoto
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
| | - Shogo Ozaki
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
| | - Tsutomu Katayama
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
| |
Collapse
|
2
|
Menikpurage IP, Woo K, Mera PE. Transcriptional Activity of the Bacterial Replication Initiator DnaA. Front Microbiol 2021; 12:662317. [PMID: 34140937 PMCID: PMC8203912 DOI: 10.3389/fmicb.2021.662317] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 04/19/2021] [Indexed: 11/13/2022] Open
Abstract
In bacteria, DnaA is the most conserved DNA replication initiator protein. DnaA is a DNA binding protein that is part of the AAA+ ATPase family. In addition to initiating chromosome replication, DnaA can also function as a transcription factor either as an activator or repressor. The first gene identified to be regulated by DnaA at the transcriptional levels was dnaA. DnaA has been shown to regulate genes involved in a variety of cellular events including those that trigger sporulation, DNA repair, and cell cycle regulation. DnaA's dual functions (replication initiator and transcription factor) is a potential mechanism for DnaA to temporally coordinate diverse cellular events with the onset of chromosome replication. This strategy of using chromosome replication initiator proteins as regulators of gene expression has also been observed in archaea and eukaryotes. In this mini review, we focus on our current understanding of DnaA's transcriptional activity in various bacterial species.
Collapse
Affiliation(s)
- Inoka P Menikpurage
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Kristin Woo
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Paola E Mera
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| |
Collapse
|
3
|
Li Y, Zhang HX, Luo WD, Lam CWK, Wang CY, Bai LP, Wong VKW, Zhang W, Jiang ZH. Profiling Ribonucleotide and Deoxyribonucleotide Pools Perturbed by Remdesivir in Human Bronchial Epithelial Cells. Front Pharmacol 2021; 12:647280. [PMID: 33995062 PMCID: PMC8120990 DOI: 10.3389/fphar.2021.647280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 03/23/2021] [Indexed: 11/13/2022] Open
Abstract
Remdesivir (RDV) has generated much anticipation for its moderate effect in treating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the unsatisfactory survival rates of hospitalized patients limit its application to the treatment of coronavirus disease 2019 (COVID-19). Therefore, improvement of antiviral efficacy of RDV is urgently needed. As a typical nucleotide analog, the activation of RDV to bioactive triphosphate will affect the biosynthesis of endogenous ribonucleotides (RNs) and deoxyribonucleotides (dRNs), which are essential to RNA and DNA replication in host cells. The imbalance of RN pools will inhibit virus replication as well. In order to investigate the effects of RDV on cellular nucleotide pools and on RNA transcription and DNA replication, cellular RNs and dRNs concentrations were measured by the liquid chromatography-mass spectrometry method, and the synthesis of RNA and DNA was monitored using click chemistry. The results showed that the IC50 values for BEAS-2B cells at exposure durations of 48 and 72 h were 25.3 ± 2.6 and 9.6 ± 0.7 μM, respectively. Ten (10) μM RDV caused BEAS-2B arrest at S-phase and significant suppression of RNA and DNA synthesis after treatment for 24 h. In addition, a general increase in the abundance of nucleotides and an increase of specific nucleotides more than 2 folds were observed. However, the variation of pyrimidine ribonucleotides was relatively slight or even absent, resulting in an obvious imbalance between purine and pyrimidine ribonucleotides. Interestingly, the very marked disequilibrium between cytidine triphosphate (CTP) and cytidine monophosphate might result from the inhibition of CTP synthase. Due to nucleotides which are also precursors for the synthesis of viral nucleic acids, the perturbation of nucleotide pools would block viral RNA replication. Considering the metabolic vulnerability of endogenous nucleotides, exacerbating the imbalance of nucleotide pools imparts great promise to enhance the efficacy of RDV, which possibly has special implications for treatment of COVID-19.
Collapse
Affiliation(s)
- Yan Li
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| | - Hui-Xia Zhang
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| | - Wen-Di Luo
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| | - Christopher Wai Kei Lam
- Faculty of Medicine and State Key Laboratory of Quality Research in Chinese Medicines, Macau University of Science and Technology, Taipa, Macau, China
| | - Cai-Yun Wang
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| | - Li-Ping Bai
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| | - Vincent Kam Wai Wong
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| | - Wei Zhang
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| | - Zhi-Hong Jiang
- State Key Laboratory of Quality Research in Chinese Medicines, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Guangdong-Hong Kong-Macao Joint Laboratory of Respiratory Infectious Disease (Macau University of Science and Technology), Taipa, Macau, China
| |
Collapse
|
4
|
Zhang M, Li W, Feng J, Gong Z, Yao Y, Zheng C. Integrative transcriptomics and proteomics analysis constructs a new molecular model for ovule abortion in the female-sterile line of Pinus tabuliformis Carr. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2020; 294:110462. [PMID: 32234230 DOI: 10.1016/j.plantsci.2020.110462] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 02/26/2020] [Accepted: 02/28/2020] [Indexed: 06/11/2023]
Abstract
Ovule development is critical to plant reproduction and free nuclear mitosis of megagametophyte (FNMM) is vital for ovule development. However, most results of ovule development were based on the studies in angiosperms, and its molecular regulation remained largely unknown in gymnosperms, particularly, during FNMM. In this context, we studied the genome-wide difference between sterile line (SL) and fertile line (FL) ovules using transcriptomics and proteomics approaches in Pinus tabuliformis Carr. Comparative analyses revealed that genes involved in DNA replication, DNA damage repair, Cell cycle, Apoptosis and Energy metabolism were highlighted. Further results showed the low expressions of MCM 2-7, RRM1, etc. perhaps led to abnormal DNA replication and damage repair, and the significantly different expressions of PARP2, CCs1, CCs3, etc. implied that the accumulated DNA double-stranded breaks were failed to be repaired and the cell cycle was arrested at G2/M in SL ovules, potentially resulting in the occurrence of apoptosis. Moreover, the deficiency of ETF-QO might hinder FNMM. Consequently, FNMM stopped and ovule aborted in SL ovules. Our results suggested a selective regulatory mechanism led to FNMM half-stop and ovule abortion in P. tabuliformis and these insights could be exploited to investigate the molecular regulations of ovule development in woody gymnosperms.
Collapse
Affiliation(s)
- Min Zhang
- College of Biological Sciences and Technology, Beijing Forestry University, No. 35, Tsinghua East Road, Beijing, 100083, China
| | - Wenhai Li
- College of Biological Sciences and Technology, Beijing Forestry University, No. 35, Tsinghua East Road, Beijing, 100083, China
| | - Jun Feng
- College of Biological Sciences and Technology, Beijing Forestry University, No. 35, Tsinghua East Road, Beijing, 100083, China
| | - Zaixin Gong
- College of Biological Sciences and Technology, Beijing Forestry University, No. 35, Tsinghua East Road, Beijing, 100083, China
| | - Yang Yao
- College of Biological Sciences and Technology, Beijing Forestry University, No. 35, Tsinghua East Road, Beijing, 100083, China
| | - Caixia Zheng
- College of Biological Sciences and Technology, Beijing Forestry University, No. 35, Tsinghua East Road, Beijing, 100083, China.
| |
Collapse
|
5
|
Abstract
The causes and consequences of spatiotemporal variation in mutation rates remain to be explored in nearly all organisms. Here we examine relationships between local mutation rates and replication timing in three bacterial species whose genomes have multiple chromosomes: Vibrio fischeri, Vibrio cholerae, and Burkholderia cenocepacia. Following five mutation accumulation experiments with these bacteria conducted in the near absence of natural selection, the genomes of clones from each lineage were sequenced and analyzed to identify variation in mutation rates and spectra. In lineages lacking mismatch repair, base substitution mutation rates vary in a mirrored wave-like pattern on opposing replichores of the large chromosomes of V. fischeri and V. cholerae, where concurrently replicated regions experience similar base substitution mutation rates. The base substitution mutation rates on the small chromosome are less variable in both species but occur at similar rates to those in the concurrently replicated regions of the large chromosome. Neither nucleotide composition nor frequency of nucleotide motifs differed among regions experiencing high and low base substitution rates, which along with the inferred ~800-kb wave period suggests that the source of the periodicity is not sequence specific but rather a systematic process related to the cell cycle. These results support the notion that base substitution mutation rates are likely to vary systematically across many bacterial genomes, which exposes certain genes to elevated deleterious mutational load. That mutation rates vary within bacterial genomes is well known, but the detailed study of these biases has been made possible only recently with contemporary sequencing methods. We applied these methods to understand how bacterial genomes with multiple chromosomes, like those of Vibrio and Burkholderia, might experience heterogeneous mutation rates because of their unusual replication and the greater genetic diversity found on smaller chromosomes. This study captured thousands of mutations and revealed wave-like rate variation that is synchronized with replication timing and not explained by sequence context. The scale of this rate variation over hundreds of kilobases of DNA strongly suggests that a temporally regulated cellular process may generate wave-like variation in mutation risk. These findings add to our understanding of how mutation risk is distributed across bacterial and likely also eukaryotic genomes, owing to their highly conserved replication and repair machinery.
Collapse
|
6
|
Transcriptome Analysis of Escherichia coli during dGTP Starvation. J Bacteriol 2016; 198:1631-44. [PMID: 27002130 DOI: 10.1128/jb.00218-16] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 03/16/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Our laboratory recently discovered that Escherichia coli cells starved for the DNA precursor dGTP are killed efficiently (dGTP starvation) in a manner similar to that described for thymineless death (TLD). Conditions for specific dGTP starvation can be achieved by depriving an E. coli optA1 gpt strain of the purine nucleotide precursor hypoxanthine (Hx). To gain insight into the mechanisms underlying dGTP starvation, we conducted genome-wide gene expression analyses of actively growing optA1 gpt cells subjected to hypoxanthine deprivation for increasing periods. The data show that upon Hx withdrawal, the optA1 gpt strain displays a diminished ability to derepress the de novo purine biosynthesis genes, likely due to internal guanine accumulation. The impairment in fully inducing the purR regulon may be a contributing factor to the lethality of dGTP starvation. At later time points, and coinciding with cell lethality, strong induction of the SOS response was observed, supporting the concept of replication stress as a final cause of death. No evidence was observed in the starved cells for the participation of other stress responses, including the rpoS-mediated global stress response, reinforcing the lack of feedback of replication stress to the global metabolism of the cell. The genome-wide expression data also provide direct evidence for increased genome complexity during dGTP starvation, as a markedly increased gradient was observed for expression of genes located near the replication origin relative to those located toward the replication terminus. IMPORTANCE Control of the supply of the building blocks (deoxynucleoside triphosphates [dNTPs]) for DNA replication is important for ensuring genome integrity and cell viability. When cells are starved specifically for one of the four dNTPs, dGTP, the process of DNA replication is disturbed in a manner that can lead to eventual death. In the present study, we investigated the transcriptional changes in the bacterium E. coli during dGTP starvation. The results show increasing DNA replication stress with an increased time of starvation, as evidenced by induction of the bacterial SOS system, as well as a notable lack of induction of other stress responses that could have saved the cells from cell death by slowing down cell growth.
Collapse
|
7
|
Tse L, Kang TM, Yuan J, Mihora D, Becket E, Maslowska KH, Schaaper RM, Miller JH. Extreme dNTP pool changes and hypermutability in dcd ndk strains. Mutat Res 2015; 784-785:16-24. [PMID: 26789486 DOI: 10.1016/j.mrfmmm.2015.12.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 12/10/2015] [Accepted: 12/17/2015] [Indexed: 11/16/2022]
Abstract
Cells lacking deoxycytidine deaminase (DCD) have been shown to have imbalances in the normal dNTP pools that lead to multiple phenotypes, including increased mutagenesis, increased sensitivity to oxidizing agents, and to a number of antibiotics. In particular, there is an increased dCTP pool, often accompanied by a decreased dTTP pool. In the work presented here, we show that double mutants of Escherichia coli lacking both DCD and NDK (nucleoside diphosphate kinase) have even more extreme imbalances of dNTPs than mutants lacking only one or the other of these enzymes. In particular, the dCTP pool rises to very high levels, exceeding even the cellular ATP level by several-fold. This increased level of dCTP, coupled with more modest changes in other dNTPs, results in exceptionally high mutation levels. The high mutation levels are attenuated by the addition of thymidine. The results corroborate the critical importance of controlling DNA precursor levels for promoting genome stability. We also show that the addition of certain exogenous nucleosides can influence replication errors in DCD-proficient strains that are deficient in mismatch repair.
Collapse
Affiliation(s)
- Lawrence Tse
- Department of Microbiology, Immunology, and Molecular Genetics, The Molecular Biology Institute, University of California and the David Geffen School of Medicine, Los Angeles, CA 90095, United States
| | - Tina Manzhu Kang
- Department of Microbiology, Immunology, and Molecular Genetics, The Molecular Biology Institute, University of California and the David Geffen School of Medicine, Los Angeles, CA 90095, United States
| | - Jessica Yuan
- Department of Microbiology, Immunology, and Molecular Genetics, The Molecular Biology Institute, University of California and the David Geffen School of Medicine, Los Angeles, CA 90095, United States
| | - Danielle Mihora
- Department of Microbiology, Immunology, and Molecular Genetics, The Molecular Biology Institute, University of California and the David Geffen School of Medicine, Los Angeles, CA 90095, United States
| | - Elinne Becket
- Department of Microbiology, Immunology, and Molecular Genetics, The Molecular Biology Institute, University of California and the David Geffen School of Medicine, Los Angeles, CA 90095, United States
| | - Katarzyna H Maslowska
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, United States
| | - Roel M Schaaper
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, United States
| | - Jeffrey H Miller
- Department of Microbiology, Immunology, and Molecular Genetics, The Molecular Biology Institute, University of California and the David Geffen School of Medicine, Los Angeles, CA 90095, United States.
| |
Collapse
|
8
|
Increase in dNTP pool size during the DNA damage response plays a key role in spontaneous and induced-mutagenesis in Escherichia coli. Proc Natl Acad Sci U S A 2011; 108:19311-6. [PMID: 22084087 DOI: 10.1073/pnas.1113664108] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Exposure of Escherichia coli to UV light increases expression of NrdAB, the major ribonucleotide reductase leading to a moderate increase in dNTP levels. The role of elevated dNTP levels during translesion synthesis (TLS) across specific replication-blocking lesions was investigated. Here we show that although the specialized DNA polymerase PolV is necessary for replication across UV-lesions, such as cyclobutane pyrimidine dimers or pyrimidine(6-4)pyrimidone photoproduct, Pol V per se is not sufficient. Indeed, efficient TLS additionally requires elevated dNTP levels. Similarly, for the bypass of an N-2-acetylaminofluorene-guanine adduct that requires Pol II instead of PolV, efficient TLS is only observed under conditions of high dNTP levels. We suggest that increased dNTP levels transiently modify the activity balance of Pol III (i.e., increasing the polymerase and reducing the proofreading functions). Indeed, we show that the stimulation of TLS by elevated dNTP levels can be mimicked by genetic inactivation of the proofreading function (mutD5 allele). We also show that spontaneous mutagenesis increases proportionally to dNTP pool levels, thus defining a unique spontaneous mutator phenotype. The so-called "dNTP mutator" phenotype does not depend upon any of the specialized DNA polymerases, and is thus likely to reflect an increase in Pol III's own replication errors because of the modified activity balance of Pol III. As up-regulation of the dNTP pool size represents a common physiological response to DNA damage, the present model is likely to represent a general and unique paradigm for TLS pathways in many organisms.
Collapse
|
9
|
Morita R, Hishinuma H, Ohyama H, Mega R, Ohta T, Nakagawa N, Agari Y, Fukui K, Shinkai A, Kuramitsu S, Masui R. An alkyltransferase-like protein from Thermus thermophilus HB8 affects the regulation of gene expression in alkylation response. J Biochem 2011; 150:327-39. [PMID: 21531768 DOI: 10.1093/jb/mvr052] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Alkylation is a type of stress that is fatal to cells. However, cells have various responses to alkylation. Alkyltransferase-like (ATL) protein is a novel protein involved in the repair of alkylated DNA; however, its repair mechanism at the molecular level is unclear. DNA microarray analysis revealed that the upregulation of 71 genes because of treatment with an alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine was related to the presence of TTHA1564, the ATL protein from Thermus thermophilus HB8. Affinity chromatography showed a direct interaction of purified TTHA1564 with purified RNA polymerase holoenzyme. The amino acid sequence of TTHA1564 is homologous to that of the C-terminal domain of Ada protein, which acts as a transcriptional activator. These results suggest that TTHA1564 might act as a transcriptional regulator. The results of DNA microarray analysis also implied that the alkylating agent induced oxidation stress in addition to alkylation stress.
Collapse
Affiliation(s)
- Rihito Morita
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Sánchez-Romero MA, Busby SJW, Dyer NP, Ott S, Millard AD, Grainger DC. Dynamic distribution of seqa protein across the chromosome of escherichia coli K-12. mBio 2010; 1:e00012-10. [PMID: 20689753 PMCID: PMC2912659 DOI: 10.1128/mbio.00012-10] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Accepted: 02/10/2010] [Indexed: 11/20/2022] Open
Abstract
The bacterial SeqA protein binds to hemi-methylated GATC sequences that arise in newly synthesized DNA upon passage of the replication machinery. In Escherichia coli K-12, the single replication origin oriC is a well-characterized target for SeqA, which binds to multiple hemi-methylated GATC sequences immediately after replication has initiated. This sequesters oriC, thereby preventing reinitiation of replication. However, the genome-wide DNA binding properties of SeqA are unknown, and hence, here, we describe a study of the binding of SeqA across the entire Escherichia coli K-12 chromosome, using chromatin immunoprecipitation in combination with DNA microarrays. Our data show that SeqA binding correlates with the frequency and spacing of GATC sequences across the entire genome. Less SeqA is found in highly transcribed regions, as well as in the ter macrodomain. Using synchronized cultures, we show that SeqA distribution differs with the cell cycle. SeqA remains bound to some targets after replication has ceased, and these targets locate to genes encoding factors involved in nucleotide metabolism, chromosome replication, and methyl transfer.
Collapse
Affiliation(s)
| | - Stephen J. W. Busby
- School of Biosciences, the University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Nigel P. Dyer
- Systems Biology Centre, Coventry House, the University of Warwick, Coventry, United Kingdom; and
| | - Sascha Ott
- Systems Biology Centre, Coventry House, the University of Warwick, Coventry, United Kingdom; and
| | - Andrew D. Millard
- Department of Biological Sciences, the University of Warwick, Coventry, United Kingdom
| | - David C. Grainger
- Department of Biological Sciences, the University of Warwick, Coventry, United Kingdom
| |
Collapse
|
11
|
Olliver A, Saggioro C, Herrick J, Sclavi B. DnaA-ATP acts as a molecular switch to control levels of ribonucleotide reductase expression in Escherichia coli. Mol Microbiol 2010; 76:1555-71. [PMID: 20487274 DOI: 10.1111/j.1365-2958.2010.07185.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ribonucleotide reductase (RNR) is the bottleneck enzyme in the synthesis of dNTPs required for DNA replication. In order to avoid the mutagenic effects of imbalances in dNTPs the amount and activity of RNR enzyme in the cell is tightly regulated. RNR expression from the nrdAB operon is thus coupled to coincide with the initiation of DNA replication. However, the mechanism for the co-ordination of gene transcription and DNA replication remains to be elucidated. The timing and synchrony of DNA replication initiation in Escherichia coli is controlled in part by the binding of the DnaA protein to the origin of replication. DnaA is also a transcription factor of the nrdAB operon and could thus be the link between these two processes. Here we show that RNA polymerase can form a stable transcription initiation complex at the nrdAB promoter by direct interaction with the far upstream sites required for the timing of expression as a function of DNA replication. In addition, we show that the binding of DnaA on the promoter can either activate or repress transcription as a function of its concentration and its nucleotide-bound state. However, transcription regulation by DnaA does not significantly affect the timing of expression of RNR from the nrdAB operon.
Collapse
Affiliation(s)
- Anne Olliver
- LBPA, UMR 8113 du CNRS, ENS Cachan, 61 Avenue du Président Wilson, 94235 Cachan, France
| | | | | | | |
Collapse
|
12
|
Poutanen M, Varhimo E, Kalkkinen N, Sukura A, Varmanen P, Savijoki K. Two-dimensional difference gel electrophoresis analysis of Streptococcus uberis in response to mutagenesis-inducing ciprofloxacin challenge. J Proteome Res 2009; 8:246-55. [PMID: 19032024 DOI: 10.1021/pr800384j] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In Streptococcus uberis, the fluoroquinolone antibiotic ciprofloxacin induces a mutagenic response that is distinct from the SOS paradigm. Two-dimensional differential gel electrophoresis was employed to investigate the effect of ciprofloxacin exposure on the proteome of S. uberis. Twenty-four protein spots exhibiting differential expression (p < 0.05) were identified as enzymes with potential role in oxidative stress, NADH generation and nucleotide biosynthesis. We suggest that these metabolic changes provide S. uberis means to stimulate mutagenesis and adaptation.
Collapse
Affiliation(s)
- Marjo Poutanen
- Institute of Biotechnology, and Department of Basic Veterinary Sciences, University of Helsinki, Finland
| | | | | | | | | | | |
Collapse
|
13
|
Functional analysis of the Streptomyces coelicolor NrdR ATP-cone domain: role in nucleotide binding, oligomerization, and DNA interactions. J Bacteriol 2008; 191:1169-79. [PMID: 19047342 DOI: 10.1128/jb.01145-08] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ribonucleotide reductases (RNRs) are essential enzymes in all living cells, providing the only known de novo pathway for the biosynthesis of deoxyribonucleotides (dNTPs), the immediate precursors of DNA synthesis and repair. RNRs catalyze the controlled reduction of all four ribonucleotides to maintain a balanced pool of dNTPs during the cell cycle. Streptomyces species contain genes, nrdAB and nrdJ, coding for oxygen-dependent class I and oxygen-independent class II RNRs, either of which is sufficient for vegetative growth. Both sets of genes are transcriptionally repressed by NrdR. NrdR contains a zinc ribbon DNA-binding domain and an ATP-cone domain similar to that present in the allosteric activity site of many class I and class III RNRs. Purified NrdR contains up to 1 mol of tightly bound ATP or dATP per mol of protein and binds to tandem 16-bp sequences, termed NrdR-boxes, present in the upstream regulatory regions of bacterial RNR operons. Previously, we showed that the ATP-cone domain alone determines nucleotide binding and that an NrdR mutant defective in nucleotide binding was unable to bind to DNA probes containing NrdR-boxes. These observations led us to propose that when NrdR binds ATP/dATP it undergoes a conformational change that affects DNA binding and hence RNR gene expression. In this study, we analyzed a collection of ATP-cone mutant proteins containing changes in residues inferred to be implicated in nucleotide binding and show that they result in pleiotrophic effects on ATP/dATP binding, on protein oligomerization, and on DNA binding. A model is proposed to integrate these observations.
Collapse
|
14
|
DnaC inactivation in Escherichia coli K-12 induces the SOS response and expression of nucleotide biosynthesis genes. PLoS One 2008; 3:e2984. [PMID: 18714349 PMCID: PMC2500167 DOI: 10.1371/journal.pone.0002984] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 07/29/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Initiation of chromosome replication in E. coli requires the DnaA and DnaC proteins and conditionally-lethal dnaA and dnaC mutants are often used to synchronize cell populations. METHODOLOGY/PRINCIPAL FINDINGS DNA microarrays were used to measure mRNA steady-state levels in initiation-deficient dnaA46 and dnaC2 bacteria at permissive and non-permissive temperatures and their expression profiles were compared to MG1655 wildtype cells. For both mutants there was altered expression of genes involved in nucleotide biosynthesis at the non-permissive temperature. Transcription of the dnaA and dnaC genes was increased at the non-permissive temperature in the respective mutant strains indicating auto-regulation of both genes. Induction of the SOS regulon was observed in dnaC2 cells at 38 degrees C and 42 degrees C. Flow cytometric analysis revealed that dnaC2 mutant cells at non-permissive temperature had completed the early stages of chromosome replication initiation. CONCLUSION/SIGNIFICANCE We suggest that in dnaC2 cells the SOS response is triggered by persistent open-complex formation at oriC and/or by arrested forks that require DnaC for replication restart.
Collapse
|
15
|
Proteomic analysis of stationary phase in the marine bacterium "Candidatus Pelagibacter ubique". Appl Environ Microbiol 2008; 74:4091-100. [PMID: 18469119 DOI: 10.1128/aem.00599-08] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
"Candidatus Pelagibacter ubique," an abundant marine alphaproteobacterium, subsists in nature at low ambient nutrient concentrations and may often be exposed to nutrient limitation, but its genome reveals no evidence of global regulatory mechanisms for adaptation to stationary phase. High-resolution capillary liquid chromatography coupled online to an LTQ mass spectrometer was used to build an accurate mass and time (AMT) tag library that enabled quantitative examination of proteomic differences between exponential- and stationary-phase "Ca. Pelagibacter ubique" cells cultivated in a seawater medium. The AMT tag library represented 65% of the predicted protein-encoding genes. "Ca. Pelagibacter ubique" appears to respond adaptively to stationary phase by increasing the abundance of a suite of proteins that contribute to homeostasis rather than undergoing a major remodeling of its proteome. Stationary-phase abundances increased significantly for OsmC and thioredoxin reductase, which may mitigate oxidative damage in "Ca. Pelagibacter," as well as for molecular chaperones, enzymes involved in methionine and cysteine biosynthesis, proteins involved in rho-dependent transcription termination, and the signal transduction enzyme CheY-FisH. We speculate that this limited response may enable "Ca. Pelagibacter ubique" to cope with ambient conditions that deprive it of nutrients for short periods and, furthermore, that the ability to resume growth overrides the need for a more comprehensive global stationary-phase response to create a capacity for long-term survival.
Collapse
|
16
|
Vlamis-Gardikas A. The multiple functions of the thiol-based electron flow pathways of Escherichia coli: Eternal concepts revisited. Biochim Biophys Acta Gen Subj 2008; 1780:1170-200. [PMID: 18423382 DOI: 10.1016/j.bbagen.2008.03.013] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2007] [Revised: 03/18/2008] [Accepted: 03/22/2008] [Indexed: 10/22/2022]
Abstract
Electron flow via thiols is a theme with many variations in all kingdoms of life. The favourable physichochemical properties of the redox active couple of two cysteines placed in the optimised environment of the thioredoxin fold allow for two electron transfers in between top biological reductants and ultimate oxidants. The reduction of ribonucleotide reductases by thioredoxin and thioredoxin reductase of Escherichia coli (E. coli) was one of the first pathways to be elucidated. Diverse functions such as protein folding in the periplasm, maturation of respiratory enzymes, detoxification of hydrogen peroxide and prevention of oxidative damage may be based on two electron transfers via thiols. A growing field is the relation of thiol reducing pathways and the interaction of E. coli with different organisms. This concept combined with the sequencing of the genomes of different bacteria may allow for the identification of fine differences in the systems employing thiols for electron flow between pathogens and their corresponding mammalian hosts. The emerging possibility is the development of novel antibiotics.
Collapse
Affiliation(s)
- Alexios Vlamis-Gardikas
- Center of Basic Research I-Biochemistry Division, Biomedical Research Foundation (BRFAA), Academy of Athens, Soranou Efessiou 4, GR-11527 Athens, Greece.
| |
Collapse
|
17
|
Herrick J, Sclavi B. Ribonucleotide reductase and the regulation of DNA replication: an old story and an ancient heritage. Mol Microbiol 2007; 63:22-34. [PMID: 17229208 DOI: 10.1111/j.1365-2958.2006.05493.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
All organisms that synthesize their own DNA have evolved mechanisms for maintaining a constant DNA/cell mass ratio independent of growth rate. The DNA/cell mass ratio is a central parameter in the processes controlling the cell cycle. The co-ordination of DNA replication with cell growth involves multiple levels of regulation. DNA synthesis is initiated at specific sites on the chromosome termed origins of replication, and proceeds bidirectionally to elongate and duplicate the chromosome. These two processes, initiation and elongation, therefore determine the total rate of DNA synthesis in the cell. In Escherichia coli, initiation depends on the DnaA protein while elongation depends on a multiprotein replication factory that incorporates deoxyribonucleotides (dNTPs) into the growing DNA chain. The enzyme ribonucleotide reductase (RNR) is universally responsible for synthesizing the necessary dNTPs. In this review we examine the role RNR plays in regulating the total rate of DNA synthesis in E. coli and, hence, in maintaining constant DNA/cell mass ratios during normal growth and under conditions of DNA stress.
Collapse
|
18
|
Abstract
Ribonucleotide reductases (RNRs) are enzymes that provide deoxyribonucleotides (dNTPs), the building blocks required for de novo DNA synthesis and repair. They are found in all organisms from prokaryotes to eukaryotes. Interestingly, in the microbial world, several organisms possess the genes encoding two, or even three different RNRs that present different structures and allosteric regulation. The finding of an increasing number of bacterial species that possess more than one RNR might suggest particular functions for these enzymes in different growth conditions. Recent support for this proposal comes from studies indicating that expression and activity of the different RNRs depends on the environment. The oxygen content as well as the redox and oxidative stresses regulate RNR activity and synthesis in various organisms. This regulation has a direct consequence on dNTP pools. An excess of dNTP pools that leads to misincorporation of dNTPs results in genetic abnormalities in eukaryotes as in prokaryotes. In contrast, increased dNTP concentrations help cells to survive under conditions where DNA has been damaged. Hence the use of different RNRs in response to various environmental conditions allows the cell to regulate the amount precisely of dNTP in both a positive and negative manner so that enough, yet not excessive, dNTPs are synthesized.
Collapse
Affiliation(s)
- Stéphanie Gon
- Department of Microbiology and Molecular Genetics, Harvard Medical School , Boston, Massachusetts, USA.
| | | |
Collapse
|
19
|
Ivanov AV, Korovina AN, Tunitskaya VL, Kostyuk DA, Rechinsky VO, Kukhanova MK, Kochetkov SN. Development of the system ensuring a high-level expression of hepatitis C virus nonstructural NS5B and NS5A proteins. Protein Expr Purif 2006; 48:14-23. [PMID: 16600628 DOI: 10.1016/j.pep.2006.02.011] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2005] [Revised: 02/07/2006] [Accepted: 02/14/2006] [Indexed: 11/27/2022]
Abstract
The plasmid pET-21d-2c-5BDelta55 effectively expressing a C-terminally truncated form (NS5BDelta55) of the hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp) was constructed. It was derived from pET-21d-5BDelta55 plasmid and contained six mutations in the ATG-start codon region and an additional cistron upstream the target gene. The C-terminally His-tagged NS5BDelta55 protein was expressed in Rosetta(DE3) Escherichia coli strain bearing an additional pRARE plasmid encoding extra copies of rare tRNAs. The yield of the target enzyme exceeded by a factor of 29 the yield of NS5BDelta55 protein expressed from the parental pET-21d-5BDelta55 plasmid (5 mg/L). The increase in the protein yield could be explained by facilitated protein translation initiation, resulted from disruption of the stable secondary mRNA structure. The pET-21d-2c-5BDelta55 plasmid yielded one third amount of the protein when expressed in BL-21(DE3) strain, indicating that the pRARE plasmid is required for a high-level expression of NS5BDelta55 protein. The 29-fold enhancement of the protein yield was accompanied by only a 2.5-fold increase of the corresponding mRNA level. The expression of another HCV NS5A protein His-tagged at the C-terminus in the developed system yielded a similar amount of the protein (4 mg/L), whereas its N-terminally His-tagged counterpart was obtained in a 30 mg/L yield. The NS5A protein purified under denaturing conditions and renatured in solution inhibited the HCV RdRp and was a substrate for human casein kinase II.
Collapse
Affiliation(s)
- Alexander V Ivanov
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, 119991, 32 Vavilov str., Moscow, Russian Federation.
| | | | | | | | | | | | | |
Collapse
|
20
|
Gon S, Camara JE, Klungsøyr HK, Crooke E, Skarstad K, Beckwith J. A novel regulatory mechanism couples deoxyribonucleotide synthesis and DNA replication in Escherichia coli. EMBO J 2006; 25:1137-47. [PMID: 16482221 PMCID: PMC1409723 DOI: 10.1038/sj.emboj.7600990] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2005] [Accepted: 01/17/2006] [Indexed: 11/08/2022] Open
Abstract
We present evidence for a complex regulatory interplay between the initiation of DNA replication and deoxyribonucleotide synthesis. In Escherichia coli, the ATP-bound DnaA protein initiates chromosomal replication. Upon loading of the beta-clamp subunit (DnaN) of the replicase, DnaA is inactivated as its intrinsic ATPase activity is stimulated by the protein Hda. The beta-subunit acts as a matchmaker between Hda and DnaA. Chain elongation of DNA requires a sufficient supply of deoxyribonucleotides (dNTPs), which are produced by ribonucleotide reductase (RNR). We present evidence suggesting that the molecular switch from ATP-DnaA to ADP-DnaA is a critical step coordinating DNA replication with increased deoxyribonucleotide synthesis. Characterization of dnaA and dnaN mutations that result in a constitutively high expression of RNR reveal this mechanism. We propose that the nucleotide bound state of DnaA regulates the transcription of the genes encoding ribonucleotide reductase (nrdAB). Accordingly, the conversion of ATP-DnaA to ADP-DnaA after initiation and loading of the beta-subunit DnaN would allow increased nrdAB expression, and consequently, coordinated RNR synthesis and DNA replication during the cell cycle.
Collapse
Affiliation(s)
- Stéphanie Gon
- Department of Microbiology, Harvard Medical School, Boston, MA, USA.
| | | | | | | | | | | |
Collapse
|
21
|
Goranov AI, Katz L, Breier AM, Burge CB, Grossman AD. A transcriptional response to replication status mediated by the conserved bacterial replication protein DnaA. Proc Natl Acad Sci U S A 2005; 102:12932-7. [PMID: 16120674 PMCID: PMC1200305 DOI: 10.1073/pnas.0506174102] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Organisms respond to perturbations in DNA replication. We characterized the global transcriptional response to inhibition of DNA replication in Bacillus subtilis. We focused on changes that were independent of the known recA-dependent global DNA damage (SOS) response. We found that overlapping sets of genes are affected by perturbations in replication elongation or initiation and that this transcriptional response serves to inhibit cell division and maintain cell viability. Approximately 20 of the operons (>50 genes) affected have potential DnaA-binding sites and are probably regulated directly by DnaA, the highly conserved replication initiation protein and transcription factor. Many of these genes have homologues and recognizable DnaA-binding sites in other bacteria, indicating that a DnaA-mediated response, elicited by changes in DNA replication status, may be conserved.
Collapse
Affiliation(s)
- Alexi I Goranov
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | | | | | | | | |
Collapse
|
22
|
Boston T, Atlung T. FNR-mediated oxygen-responsive regulation of the nrdDG operon of Escherichia coli. J Bacteriol 2003; 185:5310-3. [PMID: 12923108 PMCID: PMC180968 DOI: 10.1128/jb.185.17.5310-5313.2003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Transcription of the nrdDG operon, which encodes the class III nucleotide reductase, which is only active under anaerobic conditions, was strongly induced after a shift to anaerobiosis. The induction was completely dependent on the transcriptional activator FNR and was independent of the ArcA-ArcB two-component response regulator system. The nrdD transcript start site was mapped to a position immediately downstream of two FNR binding sites. Transcription of the other two nucleotide reductase operons, nrdAB and nrdEF, did not respond to oxygen conditions in a wild-type background, but nrdAB expression was increased in the fnr mutant under anaerobic conditions.
Collapse
Affiliation(s)
- T Boston
- Department of Life Sciences and Chemistry, Roskilde University, DK-4000 Roskilde, Denmark
| | | |
Collapse
|
23
|
MacWilliams H, Gaudet P, Deichsel H, Bonfils C, Tsang A. Biphasic expression of rnrB in Dictyostelium discoideum suggests a direct relationship between cell cycle control and cell differentiation. Differentiation 2001; 67:12-24. [PMID: 11270119 DOI: 10.1046/j.1432-0436.2001.067001012.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cell differentiation in Dictyostelium is strongly affected by the cell cycle. Cell cycle control is well-understood in other systems, but this has had almost no impact on the study of Dictyostelium cell differentiation, in part because the cell cycle in Dictyostelium is unusual, lacking a G1 phase. Here we describe the cell-cycle regulated expression of rnrB, which codes for the small subunit of ribonucleotide reductase and is a marker of late G1 in many systems. There appear to be two expression peaks, one in mid-G2 and the other near the G2/M transition. Using Xgal/anti-BrdU double staining, we show that cells in asynchronously growing cultures express in both phases, with a gap between them during which the gene is transcriptionally silent. Cold-synchronized cells show exclusively G2/M expression, while mid-G2 expression is seen in high-density synchronized cells and can also be inferred in cells undergoing synchronization by either method. rnrB expression occurs in other systems shortly after cells pass a point (the "restriction point" or "start") at which they commit to complete their current cell cycle. We demonstrate a similar commitment point in Dictyostelium and show that this occurs shortly before the mid-G2 rnrB expression peak. The Dictyostelium cell cycle thus appears to include a well-defined though inconspicuous event, between early and mid-G2, with some features which are normally associated with the G1/S transition. Others have described a switch from stalk to spore differentiation preference at about this time. Since Dictyostelium cells switch back from spore to stalk preference approximately at the G2/M rnrB expression maximum, cell differentiation as well as rnrB expression may be regulated directly by fundamental cell cycle control processes.
Collapse
Affiliation(s)
- H MacWilliams
- Zoologisches Institut, Ludwig-Maximilians-Universitat Luisenstrasse 14, 80333 München 2, Germany.
| | | | | | | | | |
Collapse
|
24
|
Abstract
Ribonucleotide reductases provide the building blocks for DNA replication in all living cells. Three different classes of enzymes use protein free radicals to activate the substrate. Aerobic class I enzymes generate a tyrosyl radical with an iron-oxygen center and dioxygen, class II enzymes employ adenosylcobalamin, and the anaerobic class III enzymes generate a glycyl radical from S-adenosylmethionine and an iron-sulfur cluster. The X-ray structure of the class I Escherichia coli enzyme, including forms that bind substrate and allosteric effectors, confirms previous models of catalytic and allosteric mechanisms. This structure suggests considerable mobility of the protein during catalysis and, together with experiments involving site-directed mutants, suggests a mechanism for radical transfer from one subunit to the other. Despite large differences between the classes, common catalytic and allosteric mechanisms, as well as retention of critical residues in the protein sequence, suggest a similar tertiary structure and a common origin during evolution. One puzzling aspect is that some organisms contain the genes for several different reductases.
Collapse
Affiliation(s)
- A Jordan
- Department of Genetics and Microbiology, Faculty of Sciences, Autonomous University of Barcelona, Bellaterra, Spain
| | | |
Collapse
|
25
|
Abstract
This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.
Collapse
Affiliation(s)
- M K Berlyn
- Department of Biology and School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06520-8104, USA.
| |
Collapse
|
26
|
Gallardo-Madueño R, Leal JF, Dorado G, Holmgren A, López-Barea J, Pueyo C. In vivo transcription of nrdAB operon and of grxA and fpg genes is triggered in Escherichia coli lacking both thioredoxin and glutaredoxin 1 or thioredoxin and glutathione, respectively. J Biol Chem 1998; 273:18382-8. [PMID: 9660805 DOI: 10.1074/jbc.273.29.18382] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously described () that Escherichia coli maintains a balanced supply of deoxyribonucleotides by a regulatory mechanism that up-regulates the levels of ribonucleotide reductase with the lack of its main hydrogen donors thioredoxin, glutaredoxin 1, and glutathione (GSH). By using a semi-quantitative reverse transcription/multiplex polymerase chain reaction fluorescent procedure that enables simultaneous analysis of up to seven mRNA species, we now demonstrate that regulation operates at the transcriptional level. Double mutant cells lacking both thioredoxin and glutaredoxin 1 had increased transcription of the nrdAB operon, as compared with the corresponding wild type parent (maximal induction of 10- and 9-fold for mRNA of nrdA and nrdB genes, respectively). Likewise, a dramatic increase of 36-fold in grxA mRNA was observed in bacteria simultaneously deficient in thioredoxin and GSH (the physiological reductant of all glutaredoxins). The increased expression of the grxA gene in trxA gshA double mutant bacteria was mimicked in trxA single mutant cells by depletion of GSH with diethylmaleate (DEM). This induction of grxA transcription was rapid since maximal increase was detected upon 10 min of DEM exposure. Like grxA expression, the basal level of fpg mRNA, encoding formamidopyrimidine-DNA glycosylase, was increased (about 4-fold) in a trxA gshA double mutant strain; this expression was also induced upon exposure to DEM (11-fold maximal induction). These results suggest that transcription of grxA might share common redox regulatory mechanism(s) with that of the fpg gene, involved in the repair of 8-oxoguanine in DNA.
Collapse
Affiliation(s)
- R Gallardo-Madueño
- Departamento de Bioquímica y Biología Molecular, Universidad de Córdoba, 14071-Córdoba, España
| | | | | | | | | | | |
Collapse
|
27
|
Jacobson BA, Fuchs JA. A 45 bp inverted repeat is required for cell cycle regulation of the Escherichia coli nrd operon. Mol Microbiol 1998; 28:1307-14. [PMID: 9680218 DOI: 10.1046/j.1365-2958.1998.00896.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Expression of beta-galactosidase from a nrd-lacZ fusion was used to determine the role in nrd regulation of an inverted sequence upstream of the promoter. Removal or replacement of a 45bp inverted repeat with an altered sequence including a 48bp perfect inverted repeat resulted in a mutant phenotype that was low in nrd expression in an exponentially growing culture and that did not increase during DNA synthesis inhibition. Changing the 22 bp in the upstream half of the inverted repeat resulted in the same phenotype, whereas changing the 22 bp in the downstream half of the inverted repeat decreased nrd expression to a lesser extent in an exponentially growing culture and had only a smaller effect on nrd expression during DNA synthesis inhibition. As other mutants with the phenotype of the upstream inverted repeat mutant were found to lack cell cycle regulation, expression of nrd-lac mRNA produced from a plasmid with this mutation in the nrd-lacZ fusion gene was compared with nrd mRNA produced from the chromosomal nrd gene in a synchronized culture. The results indicated that the upstream half of the nrd inverted repeat contains a cis-acting element essential for nrd cell cycle regulation.
Collapse
Affiliation(s)
- B A Jacobson
- Department of Biochemistry, University of Minnesota, St Paul 55108, USA
| | | |
Collapse
|
28
|
Abstract
Regulation of nrd expression in Escherichia coli by cis-acting elements was found to be more complex than previously reported. At least five upstream sites appear to positively regulate nrd expression including a Fis binding site, a DnaA binding site, an AT-rich region, an inverted repeat and a 10 bp site between the AT-rich region and the inverted repeat. Double mutants defective in these sites indicate that all sites tested act independently when regulating nrd expression. As the decrease in nrd expression in exponentially growing cultures paralleled the decrease observed in DNA synthesis-inhibited cultures for all single and double mutants, we concluded that nrd is regulated by the same mechanism in these physiological states. As mutants unable to induce nrd expression during inhibition of DNA synthesis also fail to exhibit cell cycle-regulated nrd expression, we conclude that cell cycle nrd regulation is controlled by these same sites. Site-directed mutagenesis was used to show that the absence of an increase in nrd expression during DNA inhibition previously observed for deletion of the AT-rich region results from deletion of both the Fis binding site and the AT-rich region.
Collapse
Affiliation(s)
- B A Jacobson
- Department of Biochemistry, University of Minnesota, St. Paul 55108, USA
| | | |
Collapse
|
29
|
Huang M, Elledge SJ. Identification of RNR4, encoding a second essential small subunit of ribonucleotide reductase in Saccharomyces cerevisiae. Mol Cell Biol 1997; 17:6105-13. [PMID: 9315670 PMCID: PMC232460 DOI: 10.1128/mcb.17.10.6105] [Citation(s) in RCA: 154] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Ribonucleotide reductase (RNR), which catalyzes the rate-limiting step for deoxyribonucleotide production required for DNA synthesis, is an alpha2beta2 tetramer consisting of two large and two small subunits. RNR2 encodes a small subunit and is essential for mitotic viability in Saccharomyces cerevisiae. We have cloned a second essential gene encoding a homologous small subunit, RNR4. RNR4 and RNR2 appear to have nonoverlapping functions and cannot substitute for each other even when overproduced. The lethality of RNR4 deletion mutations can be suppressed by overexpression of RNR1 and RNR3, two genes encoding the large subunit of the RNR enzyme, indicating genetic interactions among the RNR genes. RNR2 and RNR4 may be present in the same reductase complex in vivo, since they coimmunoprecipitate from cell extracts. Like the other RNR genes, RNR4 is inducible by DNA-damaging agents through the same signal transduction pathway involving MEC1, RAD53, and DUN1 kinase genes. Analysis of DNA damage inducibility of RNR2 and RNR4 revealed partial inducibility in dun1 mutants, indicating a DUN1-independent branch of the transcriptional response to DNA damage.
Collapse
Affiliation(s)
- M Huang
- Verna and Mars McLean Department of Biochemistry, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030, USA
| | | |
Collapse
|
30
|
Yang F, Curran SC, Li LS, Avarbock D, Graf JD, Chua MM, Lu G, Salem J, Rubin H. Characterization of two genes encoding the Mycobacterium tuberculosis ribonucleotide reductase small subunit. J Bacteriol 1997; 179:6408-15. [PMID: 9335290 PMCID: PMC179557 DOI: 10.1128/jb.179.20.6408-6415.1997] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Two nrdF genes, nrdF1 and nrdF2, encoding the small subunit (R2) of ribonucleotide reductase (RR) from Mycobacterium tuberculosis have 71% identity at the amino acid level and are both highly homologous with Salmonella typhimurium R2F. The calculated molecular masses of R2-1 and R2-2 are 36,588 (322 amino acids [aa]) and 36,957 (324 aa) Da, respectively. Western blot analysis of crude M. tuberculosis extracts indicates that both R2s are expressed in vivo. Recombinant R2-2 is enzymatically active when assayed with pure recombinant M. tuberculosis R1 subunit. Both ATP and dATP are activators for CDP reduction up to 2 and 1 mM, respectively. The gene encoding M. tuberculosis R2-1, nrdF1, is not linked to nrdF2, nor is either gene linked to the gene encoding the large subunit, M. tuberculosis nrdE. The gene encoding MTP64 was found downstream from nrdF1, and the gene encoding alcohol dehydrogenase was found downstream from nrdF2. A nrdA(Ts) strain of E. coli (E101) could be complemented by simultaneous transformation with M. tuberculosis nrdE and nrdF2. An M. tuberculosis nrdF2 variant in which the codon for the catalytically necessary tyrosine was replaced by the phenylalanine codon did not complement E101 when cotransformed with M. tuberculosis nrdE. Similarly, M. tuberculosis nrdF1 and nrdE did not complement E101. Activity of recombinant M. tuberculosis RR was inhibited by incubating the enzyme with a peptide corresponding to the 7 C-terminal amino acid residues of the R2-2 subunit. M. tuberculosis is a species in which a nrdEF system appears to encode the biologically active species of RR and also the only bacterial species identified so far in which class I RR subunits are not arranged on an operon.
Collapse
Affiliation(s)
- F Yang
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
31
|
Zhou P, Bogan JA, Welch K, Pickett SR, Wang HJ, Zaritsky A, Helmstetter CE. Gene transcription and chromosome replication in Escherichia coli. J Bacteriol 1997; 179:163-9. [PMID: 8981994 PMCID: PMC178675 DOI: 10.1128/jb.179.1.163-169.1997] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Transcript levels of several Escherichia coli genes involved in chromosome replication and cell division were measured in dnaC2(Ts) mutants synchronized for chromosome replication by temperature shifts. Levels of transcripts from four of the genes, dam, nrdA, mukB, and seqA, were reduced at a certain stage during chromosome replication. The magnitudes of the decreases were similar to those reported previously ftsQ and ftsZ (P. Zhou and C. E. Helmstetter, J. Bacteriol. 176:6100-6106, 1994) but considerably less than those seen with dnaA, gidA, and mioC (P. W. Theisen, J. E. Grimwade, A. C. Leonard, J. A. Bogan, and C. E. Helmstetter, Mol. Microbiol. 10:575-584, 1993). The decreases in transcripts appeared to correlate with the estimated time at which the genes replicated. This same conclusion was reached in studies with synchronous cultures obtained with the baby machine in those instances in which periodicities in transcript levels were clearly evident. The transcriptional levels for two genes, minE and tus, did not fluctuate significantly, whereas the transcripts for one gene, iciA, appeared to increase transiently. The results support the idea that cell cycle timing in E. coli is not governed by timed bursts of gene expression, since the overall findings summarized in this report are generally consistent with cell cycle-dependent transient inhibitions of transcription rather than stimulations.
Collapse
Affiliation(s)
- P Zhou
- Department of Biological Sciences, Florida Institute of Technology, Melbourne 32901, USA
| | | | | | | | | | | | | |
Collapse
|
32
|
Ormö M, Sjöberg BM. The Cys292-->Ala substitution in protein R1 of class I ribonucleotide reductase from Escherichia coli has a global effect on nucleotide binding at the specificity-determining allosteric site. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 241:363-7. [PMID: 8917431 DOI: 10.1111/j.1432-1033.1996.00363.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Ribonucleotide reductase from aerobically grown Escherichia coli is allosterically regulated, both with respect to general activity and substrate specificity. Protein R1, the homodimeric enzyme component which harbours binding sites for allosteric effectors (nucleoside triphosphates) as well as substrates (ribonucleoside diphosphates), has been engineered at Cys292 close to the dimer interaction area. This residue was earlier shown to be specifically photoaffinity labelled with the allosteric nucleotide dTTP. In this study the effect of the Cys292-->Ala substitution is shown to be an overall diminished nucleotide binding at the specificity site reflected in Kd values for dTTP, dGTP and dATP higher by more than one order of magnitude with respect to wild type. The mutant protein's interaction with other protein components of the ribonucleotide reductase system was unaffected by the mutation. These results show that Cys292 in protein R1 of class I ribonucleotide reductase from E. coli is located in the allosteric specificity site.
Collapse
Affiliation(s)
- M Ormö
- Department of Molecular Biology, Stockholm University, Sweden
| | | |
Collapse
|
33
|
Ekberg M, Sahlin M, Eriksson M, Sjöberg BM. Two conserved tyrosine residues in protein R1 participate in an intermolecular electron transfer in ribonucleotide reductase. J Biol Chem 1996; 271:20655-9. [PMID: 8702814 DOI: 10.1074/jbc.271.34.20655] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The enzyme ribonucleotide reductase consists of two nonidentical proteins, R1 and R2, which are each inactive alone. R1 contains the active site and R2 contains a stable tyrosyl radical essential for catalysis. The reduction of ribonucleotides is radical-based, and a long range electron transfer chain between the active site in R1 and the radical in R2 has been suggested. To find evidence for such an electron transfer chain in Escherichia coli ribonucleotide reductase, we converted two conserved tyrosines in R1 into phenylalanines by site-directed mutagenesis. The mutant proteins were shown to be enzymatically inactive. In addition, the mechanism-based inhibitor 2'-azido-2'-deoxy-CDP was incapable of scavenging the R2 radical, and no azido-CDP-derived radical intermediate was formed. We also show that the loss of enzymatic activity was not due to impaired R1-R2 complex formation or substrate binding. Based on these results, we predict that the two tyrosines, Tyr-730 and Tyr-731, are part of a hydrogen-bonded network that constitutes an electron transfer pathway in ribonucleotide reductase. It is demonstrated that there is no electron delocalization over these tyrosines in the resting wild-type complex.
Collapse
Affiliation(s)
- M Ekberg
- Department of Molecular Biology, University of Stockholm, S-10691 Stockholm, Sweden
| | | | | | | |
Collapse
|
34
|
Woldringh CL, Jensen PR, Westerhoff HV. Structure and partitioning of bacterial DNA: determined by a balance of compaction and expansion forces? FEMS Microbiol Lett 1995; 131:235-42. [PMID: 7557335 DOI: 10.1111/j.1574-6968.1995.tb07782.x] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The mechanisms that determine chromosome structure and chromosome partitioning in bacteria are largely unknown. Here we discuss two hypotheses: (i) the structure of the Escherichia coli nucleoid is determined by DNA binding proteins and DNA supercoiling, representing a compaction force on the one hand, and by the coupled transcription/translation/translocation of plasma membrane and cell wall proteins, representing an expansion force on the other hand; (ii) the two forces are important for the partitioning process of chromosomes.
Collapse
Affiliation(s)
- C L Woldringh
- Institute for Molecular Cell Biology, BioCentrum, University of Amsterdam, The Netherlands
| | | | | |
Collapse
|
35
|
Zhou P, Helmstetter CE. Relationship between ftsZ gene expression and chromosome replication in Escherichia coli. J Bacteriol 1994; 176:6100-6. [PMID: 7928972 PMCID: PMC196830 DOI: 10.1128/jb.176.19.6100-6106.1994] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Transcriptional levels within the ftsQAZ region of the Escherichia coli chromosome were correlated with chromosome replication and the division cycle. The transcripts were measured either in synchronous cultures generated by the baby machine technique or in dnaC2(Ts) mutants that had been aligned for initiation of chromosome replication by temperature shifts. Transcription within the ftsZ reading frame was found to fluctuate during the cell cycle, with maximal levels about midcycle and a minimum level at division, in cells growing with a doubling time of 24 min at 37 degrees C. Examination of transcription in dnaC(Ts) mutants aligned for chromosome replication indicated that the periodicity was due to a reduction in transcripts coincident with replication of the ftsQAZ region. Transcription originating upstream of the ftsA gene exhibited the periodicity and accounted for a significant proportion of the transcripts entering ftsZ. The most obvious interpretation of the data is that replication of the region transiently inhibits transcription, but alternative explanations have not been ruled out. However, no other relationship between transcription and either replication or division was detected.
Collapse
Affiliation(s)
- P Zhou
- Department of Biological Sciences, Florida Institute of Technology, Melbourne 32901
| | | |
Collapse
|
36
|
Abstract
An in vitro RNA transcription assay was used to investigate the regulation of the expression of the nrd promoter. Using a linear DNA template, we found that Fis protein, which has a positive effect on expression of the nrd promoter in an nrd-lacZ fusion in vivo, had a moderate negative effect in vitro. However, with a supercoiled DNA template as substrate, we found that Fis had a concentration-dependent positive effect on nrd transcription in vitro. This positive effect was not present on two templates that had 35- or 37-bp insertions between the Fis binding site and the nrd promoter. In the absence of Fis protein, a dramatic decrease in transcription was observed in templates with reduced supercoiling generated by the treatment with wheat germ topoisomerase I. Templates with insertions of 35 bp into an HpaII site at -102 or 37 bp into the MnlI site at -33 bp from the start of transcription failed to exhibit the DNA supercoiling sensitivity of the nrd promoter. Analysis of cells containing either of these two nrd-lacZ fusion constructs that has an insertion at the regulatory region by flow cytometry indicated that these two constructs, unlike the parental construct, were not cell cycle regulated.
Collapse
Affiliation(s)
- L Sun
- Department of Biochemistry, University of Minnesota, St. Paul 55108
| | | |
Collapse
|
37
|
Sun L, Jacobson BA, Dien BS, Srienc F, Fuchs JA. Cell cycle regulation of the Escherichia coli nrd operon: requirement for a cis-acting upstream AT-rich sequence. J Bacteriol 1994; 176:2415-26. [PMID: 8157611 PMCID: PMC205367 DOI: 10.1128/jb.176.8.2415-2426.1994] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The expression of the nrd operon encoding ribonucleotide reductase in Escherichia coli has been shown to be cell cycle regulated. To identify the cis-acting elements required for the cell cycle regulation of the nrd promoter, different 5' deletions as well as site-directed mutations were translationally fused to a lacZ reporter gene. The expression of beta-galactosidase from these nrd-lacZ fusions in single-copy plasmids was determined with synchronously growing cultures obtained by repeated phosphate starvation as well as with exponentially growing cultures by flow cytometry analysis. Although Fis and DnaA, two regulatory proteins that bind at multiple sites on the E. coli chromosome, have been found to regulate the nrd promoter, the results in this study demonstrated that neither Fis nor DnaA was required for nrd cell cycle regulation. A cis-acting upstream AT-rich sequence was found to be required for the cell cycle regulation. This sequence could be replaced by a different sequence that maintained the AT richness. A flow cytometry analysis that combined specific immunofluorescent staining of beta-galactosidase with a DNA-specific stain was developed and employed to study the nrd promoter activity in cells at specific cell cycle positions. The results of the flow cytometry analysis confirmed the results obtained from studies with synchronized cells.
Collapse
Affiliation(s)
- L Sun
- Department of Biochemistry, University of Minnesota, St. Paul 55108
| | | | | | | | | |
Collapse
|
38
|
Augustin LB, Jacobson BA, Fuchs JA. Escherichia coli Fis and DnaA proteins bind specifically to the nrd promoter region and affect expression of an nrd-lac fusion. J Bacteriol 1994; 176:378-87. [PMID: 8288532 PMCID: PMC205060 DOI: 10.1128/jb.176.2.378-387.1994] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The Escherichia coli nrd operon contains the genes encoding the two subunits of ribonucleoside diphosphate reductase. The regulation of the nrd operon has been observed to be very complex. The specific binding of two proteins to the nrd regulatory region and expression of mutant nrd-lac fusions that do not bind these proteins are described. A partially purified protein from an E. coli cell extract was previously shown to bind to the promoter region and to regulate transcription of the nrd operon (C. K. Tuggle and J. A. Fuchs, J. Bacteriol. 172:1711-1718, 1990). We have purified this protein to homogeneity by affinity chromatography and identified it as the E. coli factor for inversion stimulation (Fis). Cu-phenanthroline footprinting experiments showed that Fis binds to a site centered 156 bp upstream of the start of nrd transcription. Mutants with deletion and site-directed mutations that do not bind Fis at this site have two- to threefold-lower expression of an nrd-lac fusion. The previously reported negative regulatory nature of this site (C. K. Tuggle and J. A. Fuchs, J. Bacteriol. 172:1711-1718, 1990) was found to be due to a change in polarity in the vectors used to construct promoter fusions. Two nine-base sequences with homology to the DnaA consensus binding sequence are located immediately upstream of the nrd putative -35 RNA polymerase binding site. Binding of DnaA to these sequences on DNA fragments containing the nrd promoter region was confirmed by in vitro Cu-phenanthroline footprinting. Footprinting experiments on fragments with each as well as both of the mutated 9-mers suggests cooperativity between the two sites in binding DnaA. Assay of in vivo expression from wild-type and DnaA box-mutated nrd promoter fragments fused to lacZ on single-copy plasmids indicates a positive effect of DnaA binding on expression of nrd.
Collapse
Affiliation(s)
- L B Augustin
- Department of Biochemistry, University of Minnesota, St. Paul 55108
| | | | | |
Collapse
|
39
|
Abstract
A list of currently identified gene products of Escherichia coli is given, together with a bibliography that provides pointers to the literature on each gene product. A scheme to categorize cellular functions is used to classify the gene products of E. coli so far identified. A count shows that the numbers of genes concerned with small-molecule metabolism are on the same order as the numbers concerned with macromolecule biosynthesis and degradation. One large category is the category of tRNAs and their synthetases. Another is the category of transport elements. The categories of cell structure and cellular processes other than metabolism are smaller. Other subjects discussed are the occurrence in the E. coli genome of redundant pairs and groups of genes of identical or closely similar function, as well as variation in the degree of density of genetic information in different parts of the genome.
Collapse
Affiliation(s)
- M Riley
- Marine Biological Laboratory, Woods Hole, Massachusetts 02543
| |
Collapse
|
40
|
Elledge SJ, Zhou Z, Allen JB, Navas TA. DNA damage and cell cycle regulation of ribonucleotide reductase. Bioessays 1993; 15:333-9. [PMID: 8343143 DOI: 10.1002/bies.950150507] [Citation(s) in RCA: 188] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Ribonucleotide reductase (RNR) catalyzes the rate limiting step in the production of deoxyribonucleotides needed for DNA synthesis. In addition to the well documented allosteric regulation, the synthesis of the enzyme is also tightly regulated at the level of transcription. mRNAs for both subunits are cell cycle regulated and inducible by DNA damage in all organisms examined, including E. coli, S. cerevisiae and H. sapiens. This DNA damage regulation is thought to provide a metabolic state that facilitates DNA replicational repair processes. S. cerevisiae also encodes a second large subunit gene, RNR3, that is expressed only in the presence of DNA damage. Genetic analysis of the DNA damage response in S. cerevisiae has shown that RNR expression is under both positive and negative control. Among mutants constitutive for RNR expression are the general transcriptional repression genes, SSN6 and TUP1. Mutations in POL1 and POL3 also activate RNR expression, indicating that the DNA damage sensory network may respond directly to blocks in DNA synthesis. A protein kinase, Dun1, has been identified that controls inducibility of RNR1, RNR2 and RNR3 in response to DNA damage and replication blocks. This result suggests that the RNR genes in S. cerevisiae form a regulon that is coordinately regulated by protein phosphorylation in response to DNA damage.
Collapse
Affiliation(s)
- S J Elledge
- Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030
| | | | | | | |
Collapse
|