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Hou J, Zeng W, Zong Y, Chen Z, Miao C, Wang B, Lou C. Engineering the Ultrasensitive Transcription Factors by Fusing a Modular Oligomerization Domain. ACS Synth Biol 2018; 7:1188-1194. [PMID: 29733626 DOI: 10.1021/acssynbio.7b00414] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The dimerization and high-order oligomerization of transcription factors has endowed them with cooperative regulatory capabilities that play important roles in many cellular functions. However, such advanced regulatory capabilities have not been fully exploited in synthetic biology and genetic engineering. Here, we engineered a C-terminally fused oligomerization domain to improve the cooperativity of transcription factors. First, we found that two of three designed oligomerization domains significantly increased the cooperativity and ultrasensitivity of a transcription factor for the regulated promoter. Then, seven additional transcription factors were used to assess the modularity of the oligomerization domains, and their ultrasensitivity was generally improved, as assessed by their Hill coefficients. Moreover, we also demonstrated that the allosteric capability of the ligand-responsive domain remained intact when fusing with the designed oligomerization domain. As an example application, we showed that the engineered ultrasensitive transcription factor could be used to significantly improve the performance of a "stripe-forming" gene circuit. We envision that the oligomerization modules engineered in this study could act as a powerful tool to rapidly tune the underlying response profiles of synthetic gene circuits and metabolic pathway controllers.
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Affiliation(s)
- Junran Hou
- CAS Key Laboratory of Microbial Physiological and Metabolic Engineering and Institute of Microbiology, State Key Laboratory of Microbial Resources, Institute of Microbiology Chinese Academy of Sciences, Beijing, 100101, China
- College of Life Science, University of Chinese Academy of Science, Beijing, 100149, China
| | - Weiqian Zeng
- Institute of Molecular Precision Medicine, The Xiangya Hospital, Central South University, Changsha, Hunan 410008, P. R. China
| | - Yeqing Zong
- CAS Key Laboratory of Microbial Physiological and Metabolic Engineering and Institute of Microbiology, State Key Laboratory of Microbial Resources, Institute of Microbiology Chinese Academy of Sciences, Beijing, 100101, China
- College of Life Science, University of Chinese Academy of Science, Beijing, 100149, China
| | - Zehua Chen
- CAS Key Laboratory of Microbial Physiological and Metabolic Engineering and Institute of Microbiology, State Key Laboratory of Microbial Resources, Institute of Microbiology Chinese Academy of Sciences, Beijing, 100101, China
- College of Life Science, University of Chinese Academy of Science, Beijing, 100149, China
| | - Chensi Miao
- CAS Key Laboratory of Microbial Physiological and Metabolic Engineering and Institute of Microbiology, State Key Laboratory of Microbial Resources, Institute of Microbiology Chinese Academy of Sciences, Beijing, 100101, China
- College of Life Sciences, University of Science and Technology of China, Hefei, 230027, China
| | - Baojun Wang
- School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3FF, U.K
- Centre for Synthetic and System Biology, University of Edinburgh, Edinburgh, EH9 3FF, U.K
| | - Chunbo Lou
- CAS Key Laboratory of Microbial Physiological and Metabolic Engineering and Institute of Microbiology, State Key Laboratory of Microbial Resources, Institute of Microbiology Chinese Academy of Sciences, Beijing, 100101, China
- College of Life Science, University of Chinese Academy of Science, Beijing, 100149, China
- College of Life Sciences, University of Science and Technology of China, Hefei, 230027, China
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Benhar I, Miller C, Engelberg-Kulka H. Frameshifting in the expression of the Escherichia coli trpR gene is modulated by translation initiation. J Bacteriol 1993; 175:3204-7. [PMID: 8491735 PMCID: PMC204645 DOI: 10.1128/jb.175.10.3204-3207.1993] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The Escherichia coli trpR gene encodes the 108-amino-acid-long Trp repressor. We have shown previously that a +1 frameshifting event occurs during the expression of trpR, resulting in the synthesis of an additional (+1 frame) polypeptide. Using trpR-lac'Z fusions, we have recently found that the transition from the 0 to the +1 frame occurs via the bypassing of a 55-nucleotide-long segment of the trpR+1-lac'Z mRNA (I. Benhar, and H. Engelberg-Kulka, Cell 72:121-130, 1993). Here we show that the frequency of trpR frameshifting (or bypassing) can be regulated both in vivo and in vitro. This frequency is inversely proportional to the rate of initiation of translation of the trpR gene. Hence, modulating the level of translation initiation affects the frequency of frameshifting.
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Affiliation(s)
- I Benhar
- Department of Molecular Biology, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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Benhar I, Engelberg-Kulka H. Frameshifting in the expression of the E. coli trpR gene occurs by the bypassing of a segment of its coding sequence. Cell 1993; 72:121-30. [PMID: 8422674 DOI: 10.1016/0092-8674(93)90056-v] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The E. coli trpR gene encodes the 108 amino acid long trp repressor. We have previously shown that a +1 frameshifting event occurs during the expression of trpR. Here we show that the transition from the 0 to the +1 frame of trpR occurs by the bypassing of a 55 nt long segment of the trpR+1-lacZ mRNA. This bypassing event is not pretranslational, and it probably takes place during translation. Two adjacent elements are required: a specific sequence of trpR, which must be preceded by a nonspecific 5' end longer than 10 translatable codons. Unique to trpR-lacZ bypassing is that the 55 nt long region must be translated in frame 0 to enable bypassing into the +1 frame. Translational bypassing as a newly discovered mechanism of gene expression is discussed, and the possible existence of translational introns is suggested.
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Affiliation(s)
- I Benhar
- Department of Molecular Biology, Hebrew University, Hadassah Medical School, Jerusalem, Israel
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4
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Benhar I, Miller C, Engelberg-Kulka H. Frameshifting in the expression of the Escherichia coli trpR gene. Mol Microbiol 1992; 6:2777-84. [PMID: 1435256 DOI: 10.1111/j.1365-2958.1992.tb01457.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The trpR gene of Escherichia coli carries an open reading frame that encodes the trp repressor, 108 amino acids long. Here we show that translation of an additional (+1) reading frame of trpR occurs both in vivo and in vitro. This results in the synthesis of a stable +1 frame polypeptide. Using site-specific mutagenesis, immunological techniques and amino acid sequencing we have found that the N-terminus of the +1 frame product and that of the known 0 frame product are identical but that their C-termini differ. Our results are discussed in relation to the role of natural frameshifting as a regulatory mechanism of gene expression in general, and with respect to tryptophan biosynthesis in particular.
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Affiliation(s)
- I Benhar
- Department of Molecular Biology, Hebrew University, Hadassah Medical School, Jerusalem, Israel
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5
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Somerville R. The Trp repressor, a ligand-activated regulatory protein. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1992; 42:1-38. [PMID: 1574585 DOI: 10.1016/s0079-6603(08)60572-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- R Somerville
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
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Zhao GP, Somerville RL. Genetic and biochemical characterization of the trpB8 mutation of Escherichia coli tryptophan synthase. An amino acid switch at the sharp turn of the trypsin-sensitive "hinge" region diminishes substrate binding and alters solubility. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)48527-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Rolfes RJ, Zalkin H. Autoregulation of Escherichia coli purR requires two control sites downstream of the promoter. J Bacteriol 1990; 172:5758-66. [PMID: 2211510 PMCID: PMC526892 DOI: 10.1128/jb.172.10.5758-5766.1990] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The expression of Escherichia coli purR, which encodes the pur regulon repressor protein, is autoregulated. Autoregulation at the level of transcription requires two operator sites, designated purRo1 and purRo2 (O1 and O2). Operator O1 is in the region of DNA between the transcription start site and the site for translation initiation, and O2 is in the protein-coding region. The repressor protein binds noncooperatively to O1 with a sixfold-higher affinity than to O2, and saturation of O1 by the repressor precedes saturation of O2. Both O1 and O2 function in the two- to threefold autoregulation in vivo, as determined by measurement of beta-galactosidase and mRNA from purR-lacZ translational fusions. Of all the genes thus far known to be regulated by the Pur repressor, only purR employs a two-operator mechanism.
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Affiliation(s)
- R J Rolfes
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
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Ravnikar PD, Somerville RL. Structural and functional analysis of a cloned segment of Escherichia coli DNA that specifies proteins of a C4 pathway of serine biosynthesis. J Bacteriol 1987; 169:4716-21. [PMID: 2820941 PMCID: PMC213845 DOI: 10.1128/jb.169.10.4716-4721.1987] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The plasmid pDR121 is a pBR322 derivative that contains a 3.7-kilobase-pair EcoRI fragment of DNA from the 81.2-min region of the Escherichia coli chromosome. The genomic insert encodes threonine dehydrogenase and at least one other protein. Several physical and kinetic properties of threonine dehydrogenase, overproduced in cells harboring pDR121, are identical to those of pure threonine dehydrogenase from a haploid mutant of E. coli K-12 that produces this enzyme constitutively. Tester strains with serB or glyA mutations harboring pDR121 are prototrophs. The ability to confer prototrophy on such tester strains is associated with elevated levels of threonine dehydrogenase. The functional roles of various segments of the 3.7-kilobase-pair insert of pDR121 were analyzed by constructing specific deletions and insertions. Certain subclones retained the ability to specify threonine dehydrogenase without conferring prototrophy on tester strains. This suggests that at least one other protein encoded within pDR121 plays an essential role in the conversion of threonine to serine.
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Affiliation(s)
- P D Ravnikar
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
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Ravnikar PD, Somerville RL. Genetic characterization of a highly efficient alternate pathway of serine biosynthesis in Escherichia coli. J Bacteriol 1987; 169:2611-7. [PMID: 3108237 PMCID: PMC212135 DOI: 10.1128/jb.169.6.2611-2617.1987] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
There exists in Escherichia coli a known set of enzymes that were shown to function in an efficient and concerted way to convert threonine to serine. The sequence of reactions catalyzed by these enzymes is designated the Tut cycle (threonine utilization). To demonstrate that the relevant genes and their protein products play essential roles in serine biosynthesis, a number of mutants were analyzed. Strains of E. coli with lesions in serA, serB, serC, or glyA grew readily on minimal medium supplemented with elevated levels of leucine, arginine, lysine, threonine, and methionine. No growth on this medium was observed upon testing double mutants with lesions in one of the known ser genes plus a second lesion in glyA (serine hydroxymethyltransferase), gcv (the glycine cleavage system), or tdh (threonine dehydrogenase). Pseudorevertants of ser mutants capable of growth on either unsupplemented minimal medium or medium supplemented with low levels of leucine, arginine, lysine, threonine, and methionine were isolated. At least two unlinked mutations were associated with such phenotypes.
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Abstract
A radioimmunoassay for the Trp repressor protein of Escherichia coli was developed with antisera raised against purified Trp repressor protein. This assay was used to directly measure the intracellular Trp repressor content in several E. coli K-12 and B/r strains. Repressor levels varied from 2.5- to 3-fold in response to L-tryptophan concentration in the growth medium (15 to 44 ng of repressor per mg of protein). Neither cell growth rate nor culture age had a significant effect on repressor concentrations within the cell. Addition of L-tryptophan to the growth medium resulted in lowered intracellular levels of Trp repressor. The absolute amounts of native Trp repressor molecules per cell varied between 120 and 375 dimers in the presence and absence of L-tryptophan in the culture medium, respectively. Assuming an intracellular volume of 7.3 microliters/10(10) E. coli cells, the Trp repressor concentration varied from 270 to 850 nM in response to extracellular tryptophan levels. These findings represent the first direct measurements of Trp repressor levels in E. coli and confirm the autoregulatory nature of the trpR gene.
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Tsapakos MJ, Haydock PV, Hermodson M, Somerville RL. Ligand-mediated conformational changes in Trp repressor protein of Escherichia coli probed through limited proteolysis and the use of specific antibodies. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)36248-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Bertrand KP, Postle K, Wray LV, Reznikoff WS. Construction of a single-copy promoter vector and its use in analysis of regulation of the transposon Tn10 tetracycline resistance determinant. J Bacteriol 1984; 158:910-9. [PMID: 6327648 PMCID: PMC215528 DOI: 10.1128/jb.158.3.910-919.1984] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The construction and characterization of a promoter expression vector, lambda RS205 , is described. lambda RS205 can be used for the in vitro construction of transcriptional (operon) fusions to the lacZ gene of Escherichia coli K-12. The level of beta-galactosidase activity in lysogens of lambda RS205 fusion phages provides a quantitative measure of promoter function under single-copy conditions. The regulation of the Tn10 tetracycline resistance gene ( tetA ) and the Tn10 tet repressor gene (tetR) was examined by inserting DNA fragments that span the tetR- tetA promoter-operator region into lambda RS205 . Levels of beta-galactosidase in tetA -lacZ and tetR-lacZ fusion strains indicate that the tetA and tetR promoters are strong promoters; the tetA promoter is fourfold more active than the tetR promoter. Introduction of tetR+ plasmids into tetA -lacZ and tetR-lacZ fusion strains represses beta-galactosidase synthesis 15- to 60-fold and 6- to 15-fold, respectively. The concentration of tetracycline required to induce half-maximal beta-galactosidase synthesis in these tetR+ tet-lac strains depends on both the tetracycline resistance phenotype and the level of tetR repressor in the fusion strain. However, the induction of beta-galactosidase in isogenic tetA -lacZ and tetR-lacZ strains is coordinate. The data presented here support the current model of Tn10 tet gene organization and regulation and provide quantitative information about the regulation of tetA and tetR in vivo.
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Bogosian G, Somerville RL, Nishi K, Kano Y, Imamoto F. Transcription of the trpR gene of Escherichia coli: an autogeneously regulated system studied by direct measurements of mRNA levels in vivo. MOLECULAR & GENERAL GENETICS : MGG 1984; 193:244-50. [PMID: 6319963 DOI: 10.1007/bf00330675] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The expression of the trpR gene of Escherichia coli was investigated by measuring trpR messenger RNA levels in vivo under various physiological conditions. Trp repressor, when present, led to significant decreases in the amount of trpR message produced; this effect was enhanced by providing excess L-tryptophan to the system. In the absence of Trp repressor, no changes in trpR message levels were observed under any of the conditions employed. Sedimentation profiles of trpR mRNA revealed a single species under all circumstances. These results suggest that autogenous repression alone acts to regulate transcription of the trpR gene. The activity of the trpR promoter in vivo was evaluated using a trpR-lacZ operon fusion. Very good agreement was found between relative promoter activity and trpR message levels under all experimental conditions.
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Bogosian G, Somerville RL. Analysis in vivo of factors affecting the control of transcription initiation at promoters containing target sites for trp repressor. MOLECULAR & GENERAL GENETICS : MGG 1984; 193:110-8. [PMID: 6318045 DOI: 10.1007/bf00327423] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
An investigation of repression in the trp system of Escherichia coli was undertaken using operon fusions and plasmids constructed via recombinant DNA technology. The promoters of the trp operon and the trpR gene were fused to lacZ, enabling the activity of these promoters to be evaluated under various conditions through measurements of beta-galactosidase production. In confirmation of earlier studies, the trpR gene was shown to be regulated autogenously. This control feature of the trp system was found to maintain intracellular Trp repressor protein at essentially invariant levels under most conditions studied. Increasing the trpR+ gene dosage did not significantly elevate Trp repressor protein levels, nor did the introduction of additional operator "sinks" result in significantly decreased levels of Trp repressor protein. Definite alterations in intracellular Trp repressor protein levels were achieved only by subverting the normal trpR regulatory elements. The placement of the lacUV5 or the lambda PL promoters upstream of the trpR gene resulted in significant increases in repression of the trp system. Substituting the primary trp promoter/operator for the native trpR promoter/operator resulted in an altered regulatory response of the trp system to tryptophan limitation or excess. The regulation of the trpR gene effectively imparts a broad range of expression to the trp operon in a manner finely attuned to fluctuations in intracellular tryptophan levels.
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15
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Abstract
The structural aspects of recognition by E. coli ribosomes of translational initiation regions on homologous messenger RNAs have been reviewed. Also discussed is the location of initiation region on mRNA, its confines, typical nucleotide sequences responsible for initiation signal, and the influence of RNA macrostructure on protein synthesis initiation. Most of the published DNA nucleotide sequences surrounding the start of various E. coli genes and those of its phages have been collected.
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Haydock PV, Bogosian G, Brechling K, Somerville RL. Studies on the interaction of Trp holorepressor with several operators. Evidence that the target need not be palindromic. J Mol Biol 1983; 170:1019-30. [PMID: 6358517 DOI: 10.1016/s0022-2836(83)80201-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The interaction of Trp repressor protein with partial trp operators was studied in vitro and in vivo. At high ratios of protein to DNA, Trp holorepressor formed stable complexes with DNA molecules containing half operators. When plasmids conferring the capacity to hyperproduce Trp repressor were present in trpOc strains of Escherichia coli, repression of downstream tryptophan synthase occurred. Palindromicity of the trp operator may facilitate stable interaction with Trp repressor, but this attribute need not be regarded as a critically essential structural feature. Sufficient information for the recognition by Trp repressor protein of an appropriate target resides within a DNA sequence of approximately ten base-pairs.
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Mata-Gilsinger M, Ritzenthaler P. Physical mapping of the exuT and uxaC operators by use of exu plasmids and generation of deletion mutants in vitro. J Bacteriol 1983; 155:973-82. [PMID: 6309752 PMCID: PMC217788 DOI: 10.1128/jb.155.3.973-982.1983] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Operons uxaCA and exuT of the hexuronate system are very closely linked on the Escherichia coli genetic map. Using plasmid vectors constructed by Casadaban et al. (J. Bacteriol. 143:971-980, 1980), we formed exuT-lacZ and uxaA-lacZ fusions in vitro. The phenotypic properties of the new plasmids allowed us to confirm that the exuT and uxaCA operons are divergently transcribed. An analysis of these fusion plasmids and derivatives in the presence of multiple copies of the exuR regulatory gene demonstrated that the two operons possess separate control regions. The precise location of the operator site relative to endonuclease restriction sites was determined. In addition, deletions of different lengths were generated on exu plasmids by restriction enzymes and were recombined into the chromosome. The expression of the exu regulon genes in the resulting deletion mutants is in agreement with the postulated location of the exuT and uxaCA operators in the fusion plasmids.
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Stragier P, Patte JC. Regulation of diaminopimelate decarboxylase synthesis in Escherichia coli. III. Nucleotide sequence and regulation of the lysR gene. J Mol Biol 1983; 168:333-50. [PMID: 6350602 DOI: 10.1016/s0022-2836(83)80022-9] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The complete nucleotide sequence of the lysR gene, which encodes the activatory protein required for lysA expression, has been determined. Bal31 deletions and translational fusions were used to localize the promoter region and the initiator ATG of the lysR gene which encodes a 311 amino acid polypeptide. Both lysA and lysR coding sequences were found to be divergent and separated by a very short intergenic region consisting of 121 base-pairs between the postulated ATGs of the two proteins. Transfer of the whole lysR gene on a plasmid carrying a lysR-lacZ fusion shows that lysR expression is autoregulated by a factor of 7. The same binding site (73 base-pairs fragment) could be involved in both effects of the LysR product, acting simultaneously as an operator for lysR expression and an initiator for lysA expression. The genetic organization of the whole region (4127 base-pairs) is given. A strikingly symmetrical pattern is observed with the four tightly packed galR, lysA, lysR and orfX (an unidentified open reading frame) genes, in a very unusual arrangement of both divergent and convergent overlapping transcription units.
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Stragier P, Richaud F, Borne F, Patte JC. Regulation of diaminopimelate decarboxylase synthesis in Escherichia coli. I. Identification of a lysR gene encoding an activator of the lysA gene. J Mol Biol 1983; 168:307-20. [PMID: 6411928 DOI: 10.1016/s0022-2836(83)80020-5] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The synthesis of diaminopimelate decarboxylase, which catalyzes the decarboxylation of diaminopimelate into lysine, is known to be repressed by lysine and induced by diaminopimelate in Escherichia coli K12. Until now only mutations in lysA, the structural gene for diaminopimelate decarboxylase, have been described that lead to a Lys- phenotype. A set of plasmids carrying adjacent inserts of the lysA region was constructed and employed to transform different Lys- mutants. The complementation pattern observed and the corresponding expression of the lysA gene show that in fact the Lys- phenotype can be obtained by mutations in two different and closely linked loci: one being the lysA structural gene, and the other called lysR. We propose that the lysR gene encodes a positive effector required for the full expression of the lysA gene. The synthesis of a hybrid lysA-lacZ protein constructed in vitro was observed to be decreased dramatically in lysR mutants. Moreover, all the regulatory features were lost, indicating that the LysR activator is necessary for the regulation of lysA expression. The gene order is thyA lysA lysR clockwise around 61 minutes on the chromosome, lysA being transcribed counter-clockwise.
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20
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Johnson DI, Somerville RL. Evidence that repression mechanisms can exert control over the thr, leu, and ilv operons of Escherichia coli K-12. J Bacteriol 1983; 155:49-55. [PMID: 6408066 PMCID: PMC217650 DOI: 10.1128/jb.155.1.49-55.1983] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Mutants of Escherichia coli K-12 resistant to either the threonine analog DL-alpha-amino-beta-hydroxyvaleric acid or the leucine analog 5',5',5'-trifluoro-DL-leucine were isolated. One DL-alpha-amino-beta-hydroxyvaleric acid-resistant mutant strain, designated SP572, constitutively expressed the thr and ilv operons. The mutant allele, avr-16, was localized between trpR and the thr operon at min 0. The wildtype allele of avr-16, designated ileR, is trans dominant. One 5',5',5'-trifluoro-DL-leucine-resistant mutant strain, designated FLR9, expressed the leu and ilv operons constitutively. The mutant allele, flr-9, is linked to entA at min 13. The constitutive expression of the thr, leu, and ilv operons in mutants avr-16 and flr-9 was partly reversed in cells harboring a plasmid, which leads to elevated levels of the trpR gene product, the Trp aporepressor protein. Operator-like sequences situated upstream from the transcription startpoints of the thr, leu, and ilv operons are plausible candidates for targets of systems of repressor-operator control functioning in parallel with attenuation.
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Bogosian G, Somerville R. Trp repressor protein is capable of intruding into other amino acid biosynthetic systems. MOLECULAR & GENERAL GENETICS : MGG 1983; 191:51-8. [PMID: 6350828 DOI: 10.1007/bf00330889] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Escherichia coli strains with elevated intracellular levels of Trp repressor protein displayed complete growth inhibition on minimal media which contained high levels of tryptophan. The inhibition was attributable to the acquisition of a compound nutritional requirement, which could be satisfied by a combination of isoleucine, leucine, valine, threonine, serine, phenylalanine, and tyrosine. It is proposed that Trp repressor protein, at elevated levels, represses the transcription of those genes which encode enzymes for the biosynthesis of these particular amino acids. Data which support this model are presented, together with a discussion of its regulatory implications.
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Bogosian G, Haydock PV, Somerville RL. Indolmycin-mediated inhibition and stimulation of transcription at the trp promoter of Escherichia coli. J Bacteriol 1983; 153:1120-3. [PMID: 6337120 PMCID: PMC221749 DOI: 10.1128/jb.153.2.1120-1123.1983] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Escherichia coli cells harboring a non-attenuated trp-lac operon fusion were used to evaluate the effects of indolmycin on the initiation of transcription at the trp promoter. Indolmycin caused repression in trpR+ strains and in trpR deletion mutants, although higher effector concentrations were required in the latter situation. Plasmid-mediated elevation in tryptophanyl-tRNA synthetase reversed the inhibitory effect of indolmycin. Indolmycin did not facilitate the binding of purified Trp repressor protein to trp operator DNA.
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Kelley RL, Yanofsky C. Trp aporepressor production is controlled by autogenous regulation and inefficient translation. Proc Natl Acad Sci U S A 1982; 79:3120-4. [PMID: 7048301 PMCID: PMC346365 DOI: 10.1073/pnas.79.10.3120] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
We constructed a trpR-lacZ gene fusion that specifies a hybrid protein that has full beta-galactosidase activity. The gene fusion was associated with the unaltered trpR transcription and translation control region; thus, hybrid beta-galactosidase production was an indicator of expression of the trp aporepressor (trpR) operon. To facilitate in vivo expression studies, a DNA segment containing the trpR-lacZ gene fusion and the trpR controlling region was transferred to bacteriophage lambda and subsequently inserted into the bacterial chromosome. Analyses of hybrid beta-galactosidase production showed that the trpR operon is regulated autogenously but that the rate of synthesis of aporepressor varies only 4- to 5-fold in response to changes in the intracellular concentration of tryptophan. Under comparable conditions, the trp operon is regulated by trp repressor approximately 70-fold. Therefore, the operators of the trp operon and the trpR operon must have very different affinities for trp repressor in vivo. The promoter controlling trpR expression was found to be moderately active. Nevertheless, there are only about 50-300 molecules of trp aporepressor per cell. The low aporepressor level appears to be due to inefficient translation of trpR mRNA.
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Hugovieux-Cotte-Pattat N, Robert-Baudouy J. Regulation and transcription direction of exuR, a self-regulated repressor in escherichia coli K-12. J Mol Biol 1982; 156:221-8. [PMID: 6808145 DOI: 10.1016/0022-2836(82)90468-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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