scholarly journals SELECTION FOR A LARGE GENETIC DUPLICATION IN SALMONELLA TYPHIMURIUM

Genetics ◽  
1975 ◽  
Vol 80 (2) ◽  
pp. 227-237
Author(s):  
Daniel S Straus ◽  
George R Hoffmann
Keyword(s):  
Salmonella Typhimurium ◽  
Simple Procedure ◽  
Selective Medium ◽  
Reca Gene ◽  
Wild Type ◽  
E Coli ◽  
Selection For ◽  
Spontaneous Frequency ◽  
Very High ◽  
Tandem Duplications

ABSTRACT Salmonella typhimurium strains containing a duplication of nearly a third of the genome have been isolated by a simple procedure involving selection for improved utilization of L-malate as sole carbon source. The duplication occurs at a very high spontaneous frequency. Strains containing the duplication can be isolated selectively on malate medium, or by a non-selective procedure involving Hfr conjugation. When strains containing the duplication are maintained on non-selective medium, the duplication is readily lost. Genetic evidence suggests that the duplication is chromosomal and tandem. The fact that the recA gene is included in the duplication has been used to obtain evidence that the recA1 marker is recessive to its wild-type allele. Unlike tandem duplications previously described in E. coli, the duplication described in this report appears to have unique endpoints

scholarly journals Mutant analysis of glyceraldehyde 3-phosphate dehydrogenase in Escherichia coli

1979 ◽  
Vol 179 (1) ◽  
pp. 99-107 ◽  
Author(s):  
Jeffrey D. Hillman
Keyword(s):  
Escherichia Coli ◽  
Simple Procedure ◽  
Rabbit Antiserum ◽  
Double Diffusion ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Glycolytic Intermediate ◽  
E Coli ◽  
Catalytic Function ◽  
Mutant Strains

NAD+-specific glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.12) from Escherichia coli was purified to homogeneity by a relatively simple procedure involving affinity chromatography on agarose–hexane–NAD+ and repeated crystallization. Rabbit antiserum directed against this protein produced one precipitin line in double-diffusion studies against the pure enzyme, and two lines against crude extracts of wild-type E. coli strains. Both precipitin lines represent the interaction of antibody with determinants specific for glyceraldehyde 3-phosphate dehydrogenase. Nine independent mutants of E. coli lacking glyceraldehyde 3-phosphate dehydrogenase activity all possessed some antigenic cross-reacting material to the wild-type enzyme. The mutants could be divided into three groups on the basis of the types and amounts of precipitin lines observed in double-diffusion experiments; one group formed little cross-reacting material. The cross-reacting material in crude cell-free extracts of several of the mutant strains were also tested for alterations in their affinity for NAD+ and their phosphorylative activity. The cumulative data indicate that the protein in several of the mutant strains is severely altered, and thus that glyceraldehyde 3-phosphate dehydrogenase is unlikely to have an essential, non-catalytic function such as buffering nicotinamide nucleotide or glycolytic-intermediate concentrations. Others of the mutants tested have cross-reacting material which behaved like the wild-type enzyme for the several parameters studied; the proteins from these strains, once purified, might serve as useful analogues of the wild-type enzyme.

scholarly journals REGULATION OF NEWLY EVOLVED ENZYMES. III EVOLUTION OF THE ebg REPRESSOR DURING SELECTION FOR ENHANCED LACTASE ACTIVITY

Genetics ◽  
1977 ◽  
Vol 85 (2) ◽  
pp. 193-201
Author(s):  
Barry G Hall ◽  
Norma D Clarke
Keyword(s):  
Regulatory Gene ◽  
Enzyme Synthesis ◽  
Lactase Activity ◽  
Wild Type ◽  
Regulatory Mutation ◽  
E Coli ◽  
Lactose Induction ◽  
A Cell ◽  
Lactose Utilization ◽  
Selection For

ABSTRACT The evolution of lactose utilization by lacZ deletion strains of E. coli occurs via mutations in the ebg genes. We show that one kind of mutation in the regulatory gene ebgR results in a repressor which retains the ability to repress synthesis of ebg enzymes, but which permits 4.5-fold more ebg enzyme synthesis during lactose induction than does the wild-type repressor. A comparison between the growth rate of various ebg  + strains on lactose and the amount of ebg enzyme synthesized by these strains shows that the rate of enzyme synthesis permitted by the wild-type repressor is insufficient for growth on lactose as a sole carbon source by a cell with the most active ebg lactase yet isolated. We conclude, therefore, that the evolution of lactose utilization requires both a structural and a regulatory mutation.

ucFabV Requires Functional Reductase Activity to Confer Reduced Triclosan Susceptibility in Escherichia coli

2015 ◽  
Vol 25 (6) ◽  
pp. 394-402 ◽  
Author(s):  
Taylor L. Fischer ◽  
Robert J. White ◽  
Katherine F.K. Mares ◽  
Devin E. Molnau ◽  
Justin J. Donato
Keyword(s):  
Escherichia Coli ◽  
Reductase Activity ◽  
Acid Synthesis ◽  
Temperature Sensitive ◽  
Wild Type ◽  
E Coli ◽  
Enoyl Acp Reductase ◽  
Selection For

<b><i>Background/Aims:</i></b> We previously identified the Triclo1 fosmid in a functional metagenomic selection for clones that increased triclosan tolerance in <i>Escherichia coli</i>. The active enzyme encoded by Triclo1 is ucFabV. Although ucFabV is homologous to FabV from other organisms, ucFabV contains substitutions at key positions that would predict differences in substrate binding. Therefore, a detailed characterization of ucFabV was conducted to link its biochemical activity to its ability to confer reduced triclosan sensitivity. <b><i>Methods:</i></b> ucFabV and a catalytic mutant were purified and used to reduce crotonoyl-CoA in vitro. The mutant and wild-type enzymes were introduced into <i>E. coli</i>, and their ability to confer triclosan tolerance as well as suppress a temperature-sensitive mutant of FabI were measured. <b><i>Results:</i></b> Purified ucFabV, but not the mutant, reduced crotonoyl-CoA in vitro. The wild-type enzyme confers increased triclosan tolerance when introduced into <i>E. coli</i>, whereas the mutant remained susceptible to triclosan<i>. </i>Additionally, wild-type ucFabV, but not the mutant, functionally replaced FabI within living cells. <b><i>Conclusion:</i></b> ucFabV confers increased tolerance through its function as an enoyl-ACP reductase. Furthermore, ucFabV is capable of restoring viability in the presence of compromised FabI, suggesting ucFabV is likely facilitating an alternate step within fatty acid synthesis, bypassing FabI inhibition.

Molecular characterization ofGluconobacter oxydans recAgene and its inhibitory effect on the function of the host wild-typerecAgene

1998 ◽  
Vol 44 (2) ◽  
pp. 149-156 ◽  
Author(s):  
Yu-Tien Liu ◽  
Der-Chiang Chao ◽  
Fan Lee ◽  
Chia-Geun Chen ◽  
Dar-Der Ji
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Amino Acid ◽  
Nucleotide Sequence ◽  
Amino Acid Sequence ◽  
Reca Protein ◽  
Gluconobacter Oxydans ◽  
Inhibitory Effect ◽  
Reca Gene ◽  
Wild Type ◽  
E Coli

A DNA fragment containing the recA gene of Gluconobacter oxydans was isolated and further characterized for its nucleotide sequence and ability to functionally complement various recA mutations. When expressed in an Escherichia coli recA host, the G. oxydans recA protein could efficiently function in homologous recombination and DNA damage repair. The recA gene's nucleotide sequence analysis revealed a protein of 344 amino acids with a molecular mass of 38 kDa. We observed an E. coli-like LexA repressor-binding site in the G. oxydans recA gene promoter region, suggesting that a LexA-like mediated response system may exist in G. oxydans. The expression of G. oxydans recA in E. coli RR1, a recA+strain, surprisingly caused a remarkable reduction of the host wild-type recA gene function, whereas the expression of both Serratia marcescens recA and Pseudomonas aeruginosa recA gene caused only a slight inhibitory effect on function of the host wild-typerecA gene product. Compared with the E. coli RecA protein, the identity of the amino acid sequence of G. oxydans RecA protein is much lower than those RecA proteins of both S. marcescens and Pseudomonas aeruginosa. This result suggests that the expression of another wild-type RecA could interfere with host wild-type recA gene's function, and the extent of such an interference is possibly correlated to the identity of the amino acid sequence between the two classes of RecA protein.Key words: Gluconobacter oxydans, recA gene, recombination, SOS function, interference.

scholarly journals Balance between promiscuity and specificity in phage λ host range

2020 ◽  
Author(s):  
Bryan Andrews ◽  
Stanley Fields
Keyword(s):  
Host Range ◽  
Host Resistance ◽  
Fitness Landscape ◽  
Tail Fiber ◽  
Wild Type ◽  
E Coli ◽  
General Ability ◽  
Novel Host ◽  
Selection For ◽  
Resistance To Viruses

AbstractAs hosts acquire resistance to viruses, viruses must overcome that resistance to re-establish infectivity, or go extinct. Despite the significant hurdles associated with adapting to a resistant host, viruses are evolutionarily successful and maintain stable coevolutionary relationships with their hosts. To investigate the factors underlying how pathogens adapt to their hosts, we performed a deep mutational scan of the region of the λ tail fiber tip protein that mediates contact with the λ host, E. coli. Phages harboring amino acid substitutions were subjected to selection for infectivity on wild type E. coli, revealing a highly restrictive fitness landscape, in which most substitutions completely abrogate function. By comparing this lack of mutational tolerance to evolutionary diversity, we highlight a set of mutationally intolerant and diverse positions associated with host range expansion. Imposing selection for infectivity on three λ-resistant hosts, each harboring a different missense mutation in the λ receptor, reveals hundreds of adaptive variants in λ. We distinguish λ variants that confer promiscuity, a general ability to overcome host resistance, from those that drive host-specific infectivity. Both processes may be important in driving adaptation to a novel host.

Zur Frage des Zeitpunktes der Entscheidung zwischen abortivem oder rekombinativem Verhalten eines transduzierten Chromosomenfragmentes in der Empfängerzelle

1965 ◽  
Vol 20 (4) ◽  
pp. 284-289
Author(s):  
F. Kaudewitz ◽  
H. Schmieger
Keyword(s):  
Donor Cell ◽  
Cell Populations ◽  
Linkage Data ◽  
Wild Type ◽  
Isolated Cells ◽  
Auxotrophic Strain ◽  
Chromosomal Fragment ◽  
E Coli ◽  
Selection For ◽  
Arabinose Fermentation

In wild-type transduction of auxotrophic strain E. coli B/r/thr-1/leu-1/ara-12 colonies auxotrophic for leucine or threonine do not all arise at the same time after plating. In such crosses 48 hrs. after plating from about 20% of minute colonies grown from single abortively transduced cells there can be isolated cells capable to form genetically stable colonies prototrophic for leucine or threonine. Turbidity-measurements on cell populations derived from isolated minute colonies prove that such leu+-cells arise on the plate up to at least 96 hrs. after transduction. Linkage-data of the sites leu+-1 or thr+-1 with ara-12 for these cells disprove the occurence of the thr+ or leu+-state by backmutation. Transduction with E. coli B/r/ara-5 as donor with selection for arabinose-fermentation demonstrates the failure of delayed arising leu+ or thr+-cells in crosses yielding no minute colonies caused by abortive transduction. The experiments are discussed as evidence for the occurence of recombination between the acceptor-chromosome and the abortively transduced chromosomal fragment of a donor cell within a minute colony many cell generations after injection of this fragment.

scholarly journals Chemotactic Adaptation Is Altered by Changes in the Carboxy-Terminal Sequence Conserved among the Major Methyl-Accepting Chemoreceptors

1998 ◽  
Vol 180 (7) ◽  
pp. 1862-1868 ◽  
Author(s):  
Hisashi Okumura ◽  
So-ichiro Nishiyama ◽  
Akie Sasaki ◽  
Michio Homma ◽  
Ikuro Kawagishi
Keyword(s):  
Escherichia Coli ◽  
Salmonella Typhimurium ◽  
Physiological Significance ◽  
Wild Type ◽  
Terminal Sequence ◽  
Expression Levels ◽  
E Coli ◽  
Carboxy Terminal ◽  
Mutant Receptors

ABSTRACT In Escherichia coli and Salmonella typhimurium, methylation and demethylation of receptors are responsible for chemotactic adaptation and are catalyzed by the methyltransferase CheR and the methylesterase CheB, respectively. Among the chemoreceptors of these species, Tsr, Tar, and Tcp have a well-conserved carboxy-terminal motif (NWET/SF) that is absent in Trg and Tap. When they are expressed as sole chemoreceptors, Tsr, Tar, and Tcp support good adaptation, but Trg and Tap are poorly methylated and supported only weak adaptation. It was recently discovered that CheR binds to the NWETF sequence of Tsr in vitro. To examine the physiological significance of this binding, we characterized mutant receptors in which this pentapeptide sequence was altered. C-terminally-mutated Tar and Tcp expressed in a receptorless E. coli strain mediated responses to aspartate and citrate, respectively, but their adaptation abilities were severely impaired. Their expression levels and attractant-sensing abilities were similar to those of the wild-type receptors, but the methylation levels of the mutant receptors increased only slightly upon addition of attractants. When CheR was overproduced, both the adaptation and methylation profiles of the mutant Tar receptor became comparable to those of wild-type Tar. Furthermore, overproduction of CheR also enhanced adaptive methylation of wild-type Trg, which lacks the NWETF sequence, in the absence of any other chemoreceptor. These results suggest that the pentapeptide sequence facilitates effective adaptation and methylation by recruiting CheR.

scholarly journals Suppressors of recB mutations in Salmonella typhimurium.

Genetics ◽  
1994 ◽  
Vol 138 (1) ◽  
pp. 11-28 ◽  
Author(s):  
N R Benson ◽  
J Roth
Keyword(s):  
Escherichia Coli ◽  
Salmonella Typhimurium ◽  
Mitomycin C ◽  
Ultraviolet Light ◽  
Genetic Background ◽  
Deletion Mutants ◽  
Wild Type ◽  
Insertion And Deletion ◽  
Type Strains ◽  
Tandem Duplications

Abstract Using a screen that directly assesses transductional proficiency, we have isolated suppressors of recB mutations in Salmonella typhimurium. The alleles of sbcB reported here are phenotypically distinct from those isolated in Escherichia coli in that they restore recombination proficiency (Rec+), resistance to ultraviolet light (UVR), and mitomycin C resistance (MCR) in the absence of an accompanying sbcCD mutation. In addition the sbcB alleles reported here are co-dominant to sbcB+. We have also isolated insertion and deletion mutants of the sbcB locus. These null mutations suppress only the UVS phenotype of recB mutants. We have also isolated sbcCD mutations, which map near proC. These sbcCD mutations increase the viability, recombination proficiency and MCR of both the transductional recombination suppressors (sbcB1 & sbcB6) and the sbcB null mutations. S. typhimurium recB sbcB1 sbcCD8 strains are 15-fold more recombination proficient than wild-type strains. The increase in transductants in these strains is accompanied by a loss of abortive transductants suggesting that these fragments are accessible to the mutant recombination apparatus. Using tandem duplications, we have constructed sbcB merodiploids and found that, in a recB mutant sbcCD+ genetic background, the sbcB+ allele is dominant to sbcB1 for transductional recombination but co-dominant for UVR and MCR. However, in a recB sbcCD8 genetic background, the sbcB1 mutation is co-dominant to sbcB+ for all phenotypes. Our results lead us to suggest that the SbcB and SbcCD proteins have roles in RecBCD-dependent recombination.

scholarly journals Unusual Enterobacteriaceae: lactose-positive Salmonella typhimurium which is endemic in São Paulo, Brazil

1975 ◽  
Vol 2 (4) ◽  
pp. 349-353
Author(s):  
D P Falcão ◽  
L R Trabulsi ◽  
F W Hickman ◽  
J J Farmer
Keyword(s):  
Salmonella Typhimurium ◽  
Simple Procedure ◽  
The United States ◽  
Sao Paulo ◽  
São Paulo ◽  
True Incidence ◽  
E Coli ◽  
Phage Types ◽  
Hospital Acquired ◽  
Agar Tube

Since 1971 a lactose-positive (lac+) Salmonella typhimurium variety Copenhagen has been endemic in the city of Sao Paulo. The strain is a strong lactose fermenter and resembles Escherichia coli on primary plating media and in triple sugar iron agar. Although most isolates of the strain have uniform properties, some have slightly different antigens, antibiograms, phage types, or fermentation patterns. Most isolates have come from stools of infants under 1 year of age and are probably hospital acquired; however, other isolates are probably community acquired. Eighteen other lac+ Salmonella isolated in the United States were also studied. Most of these strains resembled E. coli on primary plates and triple sugar iron agar; thus their identification would pose a problem for most clinical laboratories. A simple procedure for detecting lac+ Salmonella mixed with lac+ E. coli consists of touching 12 colonies in succession with a straight wire and then inoculating a peptone iron agar tube. H2S production is apparent from lac+ Salmonella even if 11 E. coli and one Salmonella colony are picked. If a positive peptone iron agar tube is observed, then individual colonies are tested to rule out other strong H2S producers. The true incidence of lac+ Salmonella is unknown because they are not isolated and identified in most laboratories.

scholarly journals GENE DUPLICATION IN SACCHAROMYCES CEREVISIAE

Genetics ◽  
1978 ◽  
Vol 88 (4) ◽  
pp. 673-687
Author(s):  
P E Hansche ◽  
V Beres ◽  
P Lange
Keyword(s):  
Structural Gene ◽  
The Other ◽  
High Fidelity ◽  
Duplication Events ◽  
Selection For ◽  
The Right ◽  
Chromosome Ii ◽  
Very High ◽  
Tandem Duplications

ABSTRACT Five indepdendent duplications of the acid-phosphatase (aphtase) structural gene (acp1) were recovered from chemostat populations of S. cerevisiae that were subject to selection for in vivo hyper-aphtase activity. Two of the duplications arose spontaneously. Three of them were induced by UV. All five of the duplication events involved the transpositioning of the aphtase structural gene, acp1, and all known genes distal to acp1 on the right arm of chromosome II, to the terminus of an arm of other unknown chromosomes. One of the five duplicated regions of the right arm of chromosome II was found to be transmitted mitotically and meiotically with very high fidelity. The other four duplicated regions of the right arm of chromosome II were found to be unstable, being lost at a rate of about 2% per mitosis. However, selection for increased fidelity of mitotic transmission was effective in one of these strains. No tandem duplications of the aphtase structural gene were found.

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