scholarly journals Effect of point mutations in the lac promoter on transient and severe catabolite repression of the lac operon of Escherichia coli

1971 ◽  
Vol 123 (4) ◽  
pp. 579-584 ◽  
Author(s):  
M. D. Yudkin
Keyword(s):  
Escherichia Coli ◽  
Catabolite Repression ◽  
Point Mutations ◽  
Severe Form ◽  
Lac Operon ◽  
Wild Type ◽  
Diploid Strain ◽  
Transient Repression ◽  
Lac Promoter

1. Experiments were devised to show whether the point mutations L8 and L29 in the lac promoter alleviate transient repression. 2. Several recombinants were picked from matings between a single F−p+strain and Hfr strains carrying mutations L8 and L29. All of the 19 p−recombinants tested proved to suffer no transient repression, whereas all of the eight p+recombinants tested suffered prolonged transient repression. 3. A diploid strain was constructed in which more than 90% of the thiogalactoside transacetylase is synthesized from the episome with a wild-type lac promoter, whereas 100% of the β-galactosidase is synthesized from the chromosome with a promoter carrying mutation L8. In this diploid the synthesis of thiogalactoside transacetylase suffered transient repression but the synthesis of β-galactosidase did not. 4. Exactly similar results were obtained with a diploid strain in which the chromosomal promoter carried mutation L29. 5. The same diploid strains were used in experiments to show whether mutations L8 and L29 alleviate the severe catabolite repression caused by growth in glucose plus gluconate. In both strains glucose+gluconate repressed the synthesis of β-galactosidase much less than the synthesis of thiogalactoside transacetylase. 6. These and previously reported results can be explained by assuming (a) that both mutations L8 and L29 render the lac promoter partially, but not completely, insensitive to catabolite repression, and (b) that transient repression is an exceptionally severe form of catabolite repression.

scholarly journals Catabolite repression of the lac operon. Effect of mutations in the lac promoter

1970 ◽  
Vol 118 (5) ◽  
pp. 741-746 ◽  
Author(s):  
M. D. Yudkin
Keyword(s):  
Catabolite Repression ◽  
Point Mutations ◽  
Lac Operon ◽  
Wild Type ◽  
Diploid Strain ◽  
Promoter Mutation ◽  
Haploid Strain ◽  
Promoter Mutations ◽  
Lac Promoter ◽  
I Gene

1. Several lac diploid strains of Escherichia coli were constructed and tested to discover whether mutations in the lac promoter alleviate catabolite repression. 2. In each of these diploids the chromosome carries one of the promoter mutations, L8, L29 or L1; so that the rate of synthesis of the enzymes of the lac operon is only 2–6% of the fully induced wild-type. Each diploid harbours the episome F′lacM15 that specifies the synthesis of thiogalactoside transacetylase under the control of intact regulator, promoter and operator regions, but has a deletion in the structural gene for β-galactosidase. In each diploid more than 90% of the thiogalactoside transacetylase is synthesized from the episome, and 100% of the β-galactosidase is synthesized from the chromosome, and comparison of the extent of catabolite repression that the two enzymes suffered indicated whether the chromosomal promoter mutation relieves catabolite repression. 3. In the strains in which the promoter carries either of the point mutations L8 or L29 the enzymes were equally repressed, suggesting that neither L8 nor L29 affects catabolite repression. 4. In a diploid strain harbouring the same episome but carrying deletion L1 on the chromosome, synthesis of β-galactosidase suffered much less repression than that of thiogalactoside transacetylase. 5. In a diploid strain in which the chromosome carries L1 and also a second mutation that increases the rate of expression of lac to that permitted by L8 or L29, the synthesis of β-galactosidase again suffered much less repression than the synthesis of thiogalactoside transacetylase. 6. The effect of L1 (which deletes the boundary between the i gene and the lac promoter) is ascribed to its bringing the expression of lac under the control of the promoter of the i gene. 7. Even in strains carrying L1, some catabolite repression persists; this is not due to a trans effect from the episome since it occurs equally in a haploid strain with L1.

scholarly journals Catabolite repression of the lac operon. The contribution of transcriptional repression

1969 ◽  
Vol 114 (2) ◽  
pp. 307-311 ◽  
Author(s):  
M D Yudkin
Keyword(s):  
Escherichia Coli ◽  
Transcriptional Repression ◽  
Catabolite Repression ◽  
Type Operator ◽  
Translational Repression ◽  
Lac Operon ◽  
Wild Type ◽  
Regulator Genes ◽  
Type Strains

1. Experiments were carried out to distinguish the contributions of transcriptional and translational repression to catabolite repression of the lac operon. 2. In strain EZ16-3-G of Escherichia coli the synthesis of thiogalactoside transacetylase is directed by a gene situated on an episome, and the operator, promotor and regulator genes that lay cis to this gene have been deleted, so that the normal mechanism for controlling transcription is abolished. The extent of catabolite repression in this strain was much less than that in wild-type strains. 3. The same episome is responsible for the synthesis of thiogalactoside transacetylase in strain RM32/F′d25, and in this strain a second lac operon directs the synthesis of β-galactosidase under the control of a wild-type operator–promotor–regulator system. The extent of catabolite repression of thiogalactoside transacetylase in strain RM32/F′d25 was substantially more than in strain EZ16-3-G, but less than that of β-galactosidase in strain RM32/F′d25. 4. Since the synthesis of thiogalactoside transacetylase in these organisms is presumably subject to translational repression only, it is concluded that in strain RM32/F′d25 the synthesis of β-galactosidase is subject to both transcriptional and translational repression. It is also concluded that the extent of translational repression varies between strains.

scholarly journals Alterations in Protein Expression Caused by thehha Mutation in Escherichia coli: Influence of Growth Medium Osmolarity

1999 ◽  
Vol 181 (10) ◽  
pp. 3018-3024 ◽  
Author(s):  
Carlos Balsalobre ◽  
Jörgen Johansson ◽  
Bernt Eric Uhlin ◽  
Antonio Juárez ◽  
Francisco J. Muñoa
Keyword(s):  
Escherichia Coli ◽  
Growth Medium ◽  
Gel Electrophoresis ◽  
Catabolite Repression ◽  
Protein Pattern ◽  
Polyacrylamide Gel Electrophoresis ◽  
Wild Type ◽  
Phosphotransferase System ◽  
New Family ◽  
Medium Osmolarity

ABSTRACT The Hha protein belongs to a new family of regulators involved in the environmental regulation of virulence factors. The aim of this work was to study the effect of the hha mutation on the overall protein pattern of Escherichia coli cells by two-dimensional polyacrylamide gel electrophoresis. The growth medium osmolarity clearly influenced the effect of the hhamutation. The number of proteins whose expression was altered inhha cells, compared with wild-type cells, was three times larger at a high osmolarity than at a low osmolarity. Among the proteins whose expression was modified by the hha allele, both OmpA and protein IIAGlc of the phosphotransferase system could be identified. As this latter enzyme participates in the regulation of the synthesis of cyclic AMP and hence influences the catabolite repression system, we tested whether the expression of thelacZ gene was also modified in hha mutants. This was the case, suggesting that at least some of the pleiotropic effects of the hha mutation could be caused by its effect on the catabolite repression system.

MUTATOR GENE STUDIES IN ESCHERICHIA COLI: THE mutS GENE

Genetics ◽  
1972 ◽  
Vol 72 (4) ◽  
pp. 551-567 ◽  
Author(s):  
Edward C Cox ◽  
Gerald E Degnen ◽  
Mary L Scheppe
Keyword(s):  
Escherichia Coli ◽  
Lac Operon ◽  
Wild Type ◽  
Mutator Gene ◽  
Sense Strand ◽  
Muts Gene

ABSTRACT We report here on a study of a mutator gene (mutS) that causes transition mutations in Escherichia coli. We have used the trpA system to show that A:T→G:C and G:C→A:T transitions occur. Not all A:T pairs are equally susceptible to mutS action however, since the A:T pair at the trpA223 site reverts at a frequency similar to, if not identical with, the frequency in a mut  + background. Presumably this is a consequence of neighboring bases, because other A:T pairs are reverted by mutS in the same gene; and an A:T pair in the lac operon is reverted at two widely separated points on the chromosome, and in two orientations relative to the trp sense strand. In addition, we have shown that the mutS1 allele is recessive to wild type, and trans active.

scholarly journals Improvement of xylanase production by a parasexual cross between Aspergillus niger strains

2003 ◽  
Vol 46 (2) ◽  
pp. 177-181 ◽  
Author(s):  
Octavio Loera ◽  
Jesús Córdova
Keyword(s):  
Aspergillus Niger ◽  
Catabolite Repression ◽  
Type Strain ◽  
Wild Type Strain ◽  
Carbon Catabolite Repression ◽  
Wild Type ◽  
Diploid Strain ◽  
Xylanase Production ◽  
Parasexual Cycle ◽  
Xylanolytic Activity

A diploid strain (D4) isolated via parasexual recombination between two Aspergillus niger xylanase overproducing mutants was characterised in terms of enzyme production and catabolite repression by glucose. This strain increased xylanase production (607 nkat/ml), which was nearly 100% higher than titers achieved by the wild type strain (305 nkat/ml) and 28% higher than the best mutant used to induce parasexual cycle. Diploid D4 was also less sensitive to carbon catabolite repression by glucose, since xylanolytic activity was detected under conditions normally repressing production by the wild type strain. No decrease in maximal xylanase levels was observed in the presence of glucose for diploid D4.

scholarly journals Why Does Escherichia coli Grow More Slowly on Glucosamine than on N-Acetylglucosamine? Effects of Enzyme Levels and Allosteric Activation of GlcN6P Deaminase (NagB) on Growth Rates

2005 ◽  
Vol 187 (9) ◽  
pp. 2974-2982 ◽  
Author(s):  
Laura I. Álvarez-Añorve ◽  
Mario L. Calcagno ◽  
Jacqueline Plumbridge
Keyword(s):  
Escherichia Coli ◽  
Growth Rates ◽  
Sugar Transport ◽  
Point Mutations ◽  
Sole Source ◽  
Wild Type ◽  
Phosphotransferase System ◽  
Allosteric Activation

ABSTRACT Wild-type Escherichia coli grows more slowly on glucosamine (GlcN) than on N-acetylglucosamine (GlcNAc) as a sole source of carbon. Both sugars are transported by the phosphotransferase system, and their 6-phospho derivatives are produced. The subsequent catabolism of the sugars requires the allosteric enzyme glucosamine-6-phosphate (GlcN6P) deaminase, which is encoded by nagB, and degradation of GlcNAc also requires the nagA-encoded enzyme, N-acetylglucosamine-6-phosphate (GlcNAc6P) deacetylase. We investigated various factors which could affect growth on GlcN and GlcNAc, including the rate of GlcN uptake, the level of induction of the nag operon, and differential allosteric activation of GlcN6P deaminase. We found that for strains carrying a wild-type deaminase (nagB) gene, increasing the level of the NagB protein or the rate of GlcN uptake increased the growth rate, which showed that both enzyme induction and sugar transport were limiting. A set of point mutations in nagB that are known to affect the allosteric behavior of GlcN6P deaminase in vitro were transferred to the nagB gene on the Escherichia coli chromosome, and their effects on the growth rates were measured. Mutants in which the substrate-induced positive cooperativity of NagB was reduced or abolished grew even more slowly on GlcN than on GlcNAc or did not grow at all on GlcN. Increasing the amount of the deaminase by using a nagC or nagA mutation to derepress the nag operon improved growth. For some mutants, a nagA mutation, which caused the accumulation of the allosteric activator GlcNAc6P and permitted allosteric activation, had a stronger effect than nagC. The effects of the mutations on growth in vivo are discussed in light of their in vitro kinetics.

scholarly journals Exploitation of the Escherichia coli lac operon promoter for controlled recombinant protein production

2019 ◽  
Vol 47 (2) ◽  
pp. 755-763 ◽  
Author(s):  
Douglas F. Browning ◽  
Rita E. Godfrey ◽  
Kirsty L. Richards ◽  
Colin Robinson ◽  
Stephen J.W. Busby
Keyword(s):  
Escherichia Coli ◽  
Recombinant Protein ◽  
Recombinant Protein Production ◽  
Protein Production ◽  
Lac Operon ◽  
Lac Promoter

AbstractThe Escherichia coli lac operon promoter is widely used as a tool to control recombinant protein production in bacteria. Here, we give a brief review of how it functions, how it is regulated, and how, based on this knowledge, a suite of lac promoter derivatives has been developed to give a controlled expression that is suitable for diverse biotechnology applications.

scholarly journals The role of the regulator-gene product (repressor) in catabolite repression of β-galactosidase synthesis in Escherichia coli

1968 ◽  
Vol 106 (2) ◽  
pp. 339-343 ◽  
Author(s):  
J. Palmer ◽  
V. Moses
Keyword(s):  
Escherichia Coli ◽  
Gene Product ◽  
Catabolite Repression ◽  
Lac Repressor ◽  
Temperature Sensitive ◽  
Sensitive Mutant ◽  
Amber Suppressor ◽  
Transient Repression ◽  
I Gene

1. The specific role of the lac repressor (i-gene product) in transient catabolite repression evoked by the introduction of glucose into the medium has been investigated in Escherichia coli by using mutants of the i-gene. 2. A temperature-sensitive mutant (iTL) is normally inducible and demonstrates transient repression when grown at 32°. At 42° it is about 20% constitutive and transient catabolite repression is abolished. 3. A strain carrying an amber suppressor-sensitive mutation in the i-gene is phenotypically constitutive and also fails to show transient catabolite repression. 4. Insertion of Flaci+ into this strain restores both inducibility and transient repression. 5. It is concluded that the i-gene product interacts with the catabolite co-repressor in such a way that its affinity for the operator is increased.

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