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Abstract
The gut microbiome is an exciting new area of research in chronic liver disease. It has shown promise in expanding our understanding of these complicated disease processes and has opened up new treatment modalities. The aim of this review is to increase understanding of the microbiome and explain the collection and analysis process in the context of liver disease. It also looks at our current understanding of the role of the microbiome in the wide spectrum of chronic liver diseases and how it is being used in current therapies and treatments.
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Affiliation(s)
- Bradley Reuter
- Division of Gastroenterology, Hepatology and Nutrition, Virginia Commonwealth University, McGuire VA Medical Center, 1201 Broad Rock Boulevard, Richmond, VA 23249, USA
| | - Jasmohan S Bajaj
- Division of Gastroenterology, Hepatology and Nutrition, Virginia Commonwealth University, McGuire VA Medical Center, 1201 Broad Rock Boulevard, Richmond, VA 23249, USA.
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2
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Allaband C, McDonald D, Vázquez-Baeza Y, Minich JJ, Tripathi A, Brenner DA, Loomba R, Smarr L, Sandborn WJ, Schnabl B, Dorrestein P, Zarrinpar A, Knight R. Microbiome 101: Studying, Analyzing, and Interpreting Gut Microbiome Data for Clinicians. Clin Gastroenterol Hepatol 2019; 17:218-230. [PMID: 30240894 PMCID: PMC6391518 DOI: 10.1016/j.cgh.2018.09.017] [Citation(s) in RCA: 161] [Impact Index Per Article: 32.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Accepted: 09/13/2018] [Indexed: 02/07/2023]
Abstract
Advances in technical capabilities for reading complex human microbiomes are leading to an explosion of microbiome research, leading in turn to intense interest among clinicians in applying these techniques to their patients. In this review, we discuss the content of the human microbiome, including intersubject and intrasubject variability, considerations of study design including important confounding factors, and different methods in the laboratory and on the computer to read the microbiome and its resulting gene products and metabolites. We highlight several common pitfalls for clinicians, including the expectation that an individual's microbiome will be stable, that diet can induce rapid changes that are large compared with the differences among subjects, that everyone has essentially the same core stool microbiome, and that different laboratory and computational methods will yield essentially the same results. We also highlight the current limitations and future promise of these techniques, with the expectation that an understanding of these considerations will help accelerate the path toward routine clinical application of these techniques developed in research settings.
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Affiliation(s)
- Celeste Allaband
- Biomedical Sciences Graduate Program, University of California San Diego, La Jolla, California
| | - Daniel McDonald
- Department of Pediatrics, University of California San Diego, La Jolla, California
| | | | - Jeremiah J. Minich
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, California
| | - Anupriya Tripathi
- Division of Biological Sciences, University of California San Diego, La Jolla, California
| | - David A. Brenner
- Department of Medicine, University of California San Diego, La Jolla, California
| | - Rohit Loomba
- Department of Medicine, University of California San Diego, La Jolla, California, Center for Microbiome Innovation, University of California San Diego, La Jolla, California
| | - Larry Smarr
- Center for Microbiome Innovation, University of California San Diego, La Jolla, California, Department of Computer Science and Engineering, University of California San Diego, La Jolla, California, California Institute of Telecommunications and Information Technology, University of California San Diego, La Jolla, California
| | - William J. Sandborn
- Center for Microbiome Innovation, University of California San Diego, La Jolla, California, Division of Gastroenterology, Veterans Administration San Diego Health System, La Jolla, California
| | - Bernd Schnabl
- Department of Medicine, University of California San Diego, La Jolla, California, Center for Microbiome Innovation, University of California San Diego, La Jolla, California, Division of Gastroenterology, Veterans Administration San Diego Health System, La Jolla, California
| | - Pieter Dorrestein
- Department of Pediatrics, University of California San Diego, La Jolla, California, Center for Microbiome Innovation, University of California San Diego, La Jolla, California, Skaggs School of Pharmacy, University of California San Diego, La Jolla, California
| | - Amir Zarrinpar
- Department of Medicine, University of California San Diego, La Jolla, California, Center for Microbiome Innovation, University of California San Diego, La Jolla, California, Division of Gastroenterology, Veterans Administration San Diego Health System, La Jolla, California
| | - Rob Knight
- Department of Pediatrics, University of California San Diego, La Jolla, California; Center for Microbiome Innovation, University of California San Diego, La Jolla, California; Department of Computer Science and Engineering, University of California San Diego, La Jolla, California; Department of Bioengineering, University of California San Diego, La Jolla, California.
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3
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Singer HM, Erhardt M, Hughes KT. Comparative analysis of the secretion capability of early and late flagellar type III secretion substrates. Mol Microbiol 2014; 93:505-20. [PMID: 24946091 DOI: 10.1111/mmi.12675] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/13/2014] [Indexed: 11/28/2022]
Abstract
A remarkable feature of the flagellar-specific type III secretion system (T3SS) is the selective recognition of a few substrate proteins among the many thousand cytoplasmic proteins. Secretion substrates are divided into two specificity classes: early substrates secreted for hook-basal body (HBB) construction and late substrates secreted after HBB completion. Secretion was reported to require a disordered N-terminal secretion signal, mRNA secretion signals within the 5'-untranslated region (5'-UTR) and for late substrates, piloting proteins known as the T3S chaperones. Here, we utilized translational β-lactamase fusions to probe the secretion efficacy of the N-terminal secretion signal of fourteen secreted flagellar substrates in Salmonella enterica. We observed a surprising variety in secretion capability between flagellar proteins of the same secretory class. The peptide secretion signals of the early-type substrates FlgD, FlgF, FlgE and the late-type substrate FlgL were analysed in detail. Analysing the role of the 5'-UTR in secretion of flgB and flgE revealed that the native 5'-UTR substantially enhanced protein translation and secretion. Based on our data, we propose a multicomponent signal that drives secretion via the flagellar T3SS. Both mRNA and peptide signals are recognized by the export apparatus and together with substrate-specific chaperones allowing for targeted secretion of flagellar substrates.
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Affiliation(s)
- Hanna M Singer
- Microbiologie, Département de Médecine, Université de Fribourg, Fribourg, Switzerland
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4
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Arraiano CM. Post-transcriptional control of gene expression: bacterial mRNA degradation. World J Microbiol Biotechnol 2014; 9:421-32. [PMID: 24420109 DOI: 10.1007/bf00328030] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/1993] [Indexed: 11/30/2022]
Abstract
Many biological processes cannot be fully understood without detailed knowledge of RNA metabolism. The continuous breakdown and resynthesis of prokaryotic mRNA permit rapid production of new kinds of proteins. In this way, mRNA levels can regulate protein synthesis and cellular growth. Analysing mRNA degradation in prokaryotes has been particularly difficult because most mRNA undergo rapid exponential decay. Prokaryotic mRNAs differ in their susceptibility to degradation by endonucleases and exonucleases, possibly because of variation in their sequencing and structure. In spite of numerous studies, details of mRNA degradation are still largely unknown. This review highlights those aspects of mRNA metabolism which seem most influential in the regulation of gene expression.
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Affiliation(s)
- C M Arraiano
- Instituto de Tecnologia Quimica e Biológica (ITQB), Apt 127, 2780, Oeiras, Portugal
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5
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Bernstein JA, Khodursky AB, Lin PH, Lin-Chao S, Cohen SN. Global analysis of mRNA decay and abundance in Escherichia coli at single-gene resolution using two-color fluorescent DNA microarrays. Proc Natl Acad Sci U S A 2002; 99:9697-702. [PMID: 12119387 PMCID: PMC124983 DOI: 10.1073/pnas.112318199] [Citation(s) in RCA: 627] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/27/2002] [Indexed: 11/18/2022] Open
Abstract
Much of the information available about factors that affect mRNA decay in Escherichia coli, and by inference in other bacteria, has been gleaned from study of less than 25 of the approximately 4,300 predicted E. coli messages. To investigate these factors more broadly, we examined the half-lives and steady-state abundance of known and predicted E. coli mRNAs at single-gene resolution by using two-color fluorescent DNA microarrays. An rRNA-based strategy for normalization of microarray data was developed to permit quantitation of mRNA decay after transcriptional arrest by rifampicin. We found that globally, mRNA half-lives were similar in nutrient-rich media and defined media in which the generation time was approximately tripled. A wide range of stabilities was observed for individual mRNAs of E. coli, although approximately 80% of all mRNAs had half-lives between 3 and 8 min. Genes having biologically related metabolic functions were commonly observed to have similar stabilities. Whereas the half-lives of a limited number of mRNAs correlated positively with their abundance, we found that overall, increased mRNA stability is not predictive of increased abundance. Neither the density of putative sites of cleavage by RNase E, which is believed to initiate mRNA decay in E. coli, nor the free energy of folding of 5' or 3' untranslated region sequences was predictive of mRNA half-life. Our results identify previously unsuspected features of mRNA decay at a global level and also indicate that generalizations about decay derived from the study of individual gene transcripts may have limited applicability.
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Affiliation(s)
- Jonathan A Bernstein
- Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA
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6
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Abstract
Post-transcriptional mechanisms operate in regulation of gene expression in bacteria, the amount of a given gene product being also dependent on the inactivation rate of its own message. Moreover, segmental differences in mRNA stability of polycistronic transcripts may be responsible for differential expression of genes clustered in operons. Given the absence of 5' to 3' exoribonucleolytic activities in prokaryotes, both endoribonucleases and 3' to 5' exoribonucleases are involved in chemical decay of mRNA. As the 3' to 5' exoribonucleolytic activities are readily blocked by stem-loop structures which are usual at the 3' ends of bacterial messages, the rate of decay is primarily determined by the rate of the first endonucleolytic cleavage within the transcripts, after which the resulting mRNA intermediates are degraded by the 3' to 5' exoribonucleases. Consequently, the stability of a given transcript is determined by the accessibility of suitable target sites to endonucleolytic activities. A considerable number of bacterial messages decay with a net 5' to 3' directionality. Two different alternative models have been proposed to explain such a finding, the first invoking the presence of functional coupling between degradation and the movement of the ribosomes along the transcripts, the second one implying the existence of a 5' to 3' processive '5' binding nuclease'. The different systems by which these two current models of mRNA decay have been tested will be presented with particular emphasis on polycistronic transcripts.
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Affiliation(s)
- P Alifano
- Dipartimento di Biologia e Patologia Cellulare e Molecolare L. Califano, Università di Napoli Federico II, Italy
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7
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Balbas P, Bolivar F. Design and construction of expression plasmid vectors in Escherichia coli. Methods Enzymol 1990; 185:14-37. [PMID: 2199776 DOI: 10.1016/0076-6879(90)85005-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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8
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Newbury SF, Smith NH, Robinson EC, Hiles ID, Higgins CF. Stabilization of translationally active mRNA by prokaryotic REP sequences. Cell 1987; 48:297-310. [PMID: 2433046 DOI: 10.1016/0092-8674(87)90433-8] [Citation(s) in RCA: 263] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The REP sequence is a highly conserved inverted repeat that is present in about 25% of all E. coli transcription units. We show that the REP sequence can stabilize upstream RNA, independently of any other sequences, by protection from 3'-5' exonuclease attack. The REP sequence is frequently responsible for the differential stability of different segments of mRNA within an operon. We demonstrate that REP-stabilized mRNA can be translated in vivo and that cloning the REP sequence downstream of a gene can increase protein synthesis. This provides direct evidence that alterations in mRNA stability can play a role in determining bacterial gene expression. The implications of these findings for the mechanisms of mRNA degradation and for the role of RNA stability in the regulation of gene expression are discussed.
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Polynucleotide phosphorylase and ribonuclease II are required for cell viability and mRNA turnover in Escherichia coli K-12. Proc Natl Acad Sci U S A 1986; 83:120-4. [PMID: 2417233 PMCID: PMC322803 DOI: 10.1073/pnas.83.1.120] [Citation(s) in RCA: 326] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The isolation of a temperature-sensitive allele of RNase II (rnb) by in vitro mutagenesis has permitted the demonstration that RNase II and polynucleotide phosphorylase (PNPase) are required for cell viability and mRNA turnover in Escherichia coli. Double-mutant strains carrying the pnp-7 and rnb-500 alleles (PNPase deficient and RNase II thermolabile) ceased growing in Luria broth within 30 min after shift to the nonpermissive temperature. Cessation of growth was accompanied by an accumulation of mRNA fragments 100-1500 nucleotides long. In contrast, single-mutant and wild-type control strains grew normally at the nonpermissive temperature and did not accumulate mRNA. No significant changes in rRNA patterns were observed in any of the strains.
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10
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Casjens S, Adams MB. Posttranscriptional modulation of bacteriophage P22 scaffolding protein gene expression. J Virol 1985; 53:185-91. [PMID: 3880826 PMCID: PMC255005 DOI: 10.1128/jvi.53.1.185-191.1985] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The bacteriophage P22 late operon contains 2 genes whose products are required for cell lysis and 13 genes whose products are involved in the morphogenesis of the phage particle. This operon is under the positive control of the phage gene 23 product and is thought to have a single promoter. The expression of one of these late genes, the scaffolding protein gene, is autogenously modulated independently from the remainder of the late genes. When unassembled, scaffolding protein turns down the rate of synthesis of additional scaffolding protein, and when it is assembled into phage precursor structures, it does not. Experiments presented here show (i) that the mRNA from the scaffolding protein gene is functionally threefold more stable when most of the scaffolding protein is assembled than when it is unassembled and (ii) that no new promoter near the scaffolding protein gene is activated at the high level of synthesis. These data support the model that this autogenous modulation occurs at a posttranscriptional level. We also observed that another message, that of coat protein, appears to become increasingly stable with time after phage infection.
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11
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Stern MJ, Ames GF, Smith NH, Robinson EC, Higgins CF. Repetitive extragenic palindromic sequences: a major component of the bacterial genome. Cell 1984; 37:1015-26. [PMID: 6378385 DOI: 10.1016/0092-8674(84)90436-7] [Citation(s) in RCA: 456] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
We describe a remarkably conserved nucleotide sequence, the many copies of which may occupy up to 1% of the genomes of E. coli and S. typhimurium. This sequence, the REP (repetitive extragenic palindromic) sequence, is about 35 nucleotides long, includes an inverted repeat, and can occur singly or in multiple adjacent copies. A possible role for the REP sequences in regulation of gene expression has been thoroughly investigated. While the REP sequences do not appear to modulate differential gene expression within an operon, they can affect the expression of both upstream and downstream genes to a small extent, probably by affecting the rate of mRNA degradation. Possible roles for the REP sequence in mRNA degradation, chromosome structure, and recombination are discussed.
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12
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Crofton S, Dennis PP. Cloning and orientation of the gene encoding polynucleotide phosphorylase in Escherichia coli. J Bacteriol 1983; 154:58-64. [PMID: 6300041 PMCID: PMC217430 DOI: 10.1128/jb.154.1.58-64.1983] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Mutations which affect the activity of polynucleotide phosphorylase (PNPase) map near 69 min on the bacterial chromosome. This region of the chromosome has been cloned by inserting the kanamycin-resistant transposon Tn5 near the argG and mtr loci at 68.5 min. Large SalI fragments of chromosomal DNA containing the Tn5 element were inserted into pBR322, and selection was made for kanamycin-resistant recombinant plasmids. Two of these plasmids were found to produce high levels of PNPase activity in both wild-type and host strains lacking PNPase activity. The pnp gene was further localized and subcloned on a 4.8 kilobase HindIII-EcoRI fragment. This fragment was shown to encode an 84,000-molecular weight protein which comigrated with purified PNPase during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The orientation of the pnp gene was determined by insertion of Tn5 into the 4.8 kilobase fragment cloned in pBR322. Some of the insertions had lost the ability to elevate the level of PNPase activity in the host bacterium. Restriction mapping of the positions of the Tn5 insertions and analysis of plasmid-encoded polypeptides in UV-irradiated maxi-cells indicated that the pnp gene is oriented in the counterclockwise direction on the bacterial chromosome.
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13
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Littauer U, Soreq H. 17 Polynucleotide Phosphorylase. ACTA ACUST UNITED AC 1982. [DOI: 10.1016/s1874-6047(08)60289-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2023]
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14
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Portier C, Migot C, Grumberg-Manago M. Cloning of E. coli pnp gene from an episome. MOLECULAR & GENERAL GENETICS : MGG 1981; 183:298-305. [PMID: 6276682 DOI: 10.1007/bf00270632] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Starting with an F' episome harboring a transposon inserted in the pnp gene (Portier 1980), we were able to identify an EcoRI restriction fragment carrying the pnp and argG genes. This fragment, from both wild-type and mutant episomes, was cloned ni pACYC184. The presence of argG on the fragment allowed positive selection of the desired clones in an auxotrophic strain (argG). A restriction map was established and a fragment of 3 megadaltons subcloned in the plasmid vector pBR322. The pnp gene corresponds to about 50% of this subcloned segment and was roughly located by deletion mapping. The direction of transcription and locations of the promotor and gene extremities were determined by analyzing proteins synthesized in "maxi-cells". In addition, the gene coding for a 10,000 dalton protein was found to reside adjacent to the beginning of the pnp structural gene. Strains carrying plasmids which express the pnp overproduce polynucleotide phosphorylase.
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Portier C. Isolation of a polynucleotide phosphorylase mutant using a kanamycin resistant determinant. MOLECULAR & GENERAL GENETICS : MGG 1980; 178:343-9. [PMID: 6248726 DOI: 10.1007/bf00270482] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Insertion in an episome of a kanamycine-resistant element (Tn5) at the polynucleotide phosphorylase gene level, results, after transduction into a wild strain, by the loss of activities specific to polynucleotide phosphorylase. A low phosphorolytic activity is nevertheless detectable in crude extracts, but no longer in extracts slightly purified after heat treatment at 54 degrees C. The part played by other enzymes in these activities is discussed. Bacterial growth is not affected by introduction of the mutation.
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Ono M, Kuwano M. Chromosomal location of a gene for chemical longevity of messenger ribonculeic acid in a temperature-sensitive mutant of Escherichia coli. J Bacteriol 1980; 142:325-6. [PMID: 6154687 PMCID: PMC293961 DOI: 10.1128/jb.142.1.325-326.1980] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Genetic analysis of a thermolabile mutation affecting alteration of messenger ribonculeic acid stability indicates that the gene ams maps close to pyrC gene (23 min) on the Escherichia coli chromosome and has a cotransduction frequency of 29.6% with pyrC gene. The probable gene order is pyrD-ams-pyrC-purB.
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18
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Cohen T, Silberstein A, Kuhn J, Tal M. Relief of polarity in E. coli depleted of 30S ribosomal subunits. MOLECULAR & GENERAL GENETICS : MGG 1979; 173:127-34. [PMID: 386031 DOI: 10.1007/bf00330302] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Escherichia coli was depleted of ribosomes by a thermal shock at 47 degrees C which quantitatively destroyed the 30S ribosomal subunits. During recovery in minimal medium at 30 degrees C RNA is synthesized while protein synthesis resumes only after about 90 min. It is shown that lac mRNA is synthesized in the complete absence of ribosomal activity and hence RNA synthesis is not coupled to protein synthesis. Lac mRNA from a series of lac nonsense mutants was examined in both heated and untreated cells. It was found that the polar effect of nonsense mutation is relieved in the absence of ribosomes and that this relief is due to the synthesis of larger mRNA molecules. Since Rho remained active in thermally treated cells, premature termination at secondary signals within the lac operon must also depend on the presence of active ribosomes.
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