Hyperproduction of aspartase by a catabolite repression-resistant mutant of Escherichia coli B harboring multicopy aspA and par recombinant plasmids

Recombinant plasmids bearing the Escherichia coli K-12 aspartase gene (aspA) and the plasmid partition locus (par) were introduced into a catabolite repression-resistant strain of E. coli B, AT202, constructed by mutational and transductional methods. Plasmid pNK101(pBR322-aspA-par) was stably maintained in cells of AT202 even after 30 cell generations, while pYT471(pBR322-aspA), which bore no par locus, was lost at high frequencies from the host cells. Strain AT202 harboring pNK101 produced 3-fold and 80-fold more aspartase than the wild-type E. coli B harboring pNK101 and the wild-type E. coli B strain, respectively. The maximum amount of aspA product (aspartase) was 40–45% of the total cellular protein.     

Increased production of aspartase in Escherichia coli K-12 by use of stabilized aspA recombinant plasmid

Recombinant plasmid pYT471, which consists of the aspartase gene (aspA) and the multicopy vector pBR322, was lost from cells of Escherichia coli K-12 at high frequencies in medium in which aspartase was abundantly formed due to release from catabolite repression. This plasmid loss was not completely prevented by the selective pressure of antibiotic addition. To increase the stability of the aspA plasmid, pNK101 (pBR322::aspA-par) was constructed by using the partition locus (par) derived from the low-copy vector pSC101. In E. coli K-12 cells, pNK101 was lost at a frequency as low as 0.4% per cell generation in nonselective medium, whereas pYT471 was lost at a frequency as high as 8.5%. Cells harboring this stable plasmid produced ca. 30-fold more aspartase than did cells harboring the unstable plasmid after 30 cell generations. Thus, we could increase aspartase production by stabilizing the aspA recombinant plasmid.     

Increased production of aspartase in Escherichia coli K-12 by use of stabilized aspA recombinant plasmid.

Recombinant plasmid pYT471, which consists of the aspartase gene (aspA) and the multicopy vector pBR322, was lost from cells of Escherichia coli K-12 at high frequencies in medium in which aspartase was abundantly formed due to release from catabolite repression. This plasmid loss was not completely prevented by the selective pressure of antibiotic addition. To increase the stability of the aspA plasmid, pNK101 (pBR322::aspA-par) was constructed by using the partition locus (par) derived from the low-copy vector pSC101. In E. coli K-12 cells, pNK101 was lost at a frequency as low as 0.4% per cell generation in nonselective medium, whereas pYT471 was lost at a frequency as high as 8.5%. Cells harboring this stable plasmid produced ca. 30-fold more aspartase than did cells harboring the unstable plasmid after 30 cell generations. Thus, we could increase aspartase production by stabilizing the aspA recombinant plasmid.     

Aspartase-hyperproducing mutants of Escherichia coli B.

When a wild-type strain of Escherichia coli B was cultured on a medium containing L-aspartic acid as the sole carbon source (Asp-C medium), aspartase formation was higher than that observed in minimal medium. Addition of glucose to Asp-C medium decreased aspartase formation. When also cultured in a medium containing L-aspartic acid as the sole nitrogen source (Asp-N medium), E. coli B showed a low level of aspartase formation and an elongated doubling time. To obtain aspartase-hyperproducing strains, we enriched cells growing faster than cells of the wild-type strain in Asp-N medium by continuous cultivation of mutagenized cells. After plate selection, the doubling times of these mutants were measured. Thereafter, fast-growing mutants were tested for aspartase formation. One of these mutants, strain EAPc7, had a higher level of aspartase formation than did the wild-type strain in medium containing L-aspartic acid as the carbon source, however; addition of glucose to this medium decreased aspartase formation. The other mutant, strain EAPc244, had a higher level of aspartase activity than did the wild-type strain in both media. Therefore, aspartase formation in mutant EAPc244 was released from catabolite repression. In strain EAPc244 the other catabolite-repressible enzymes, beta-galactosidase, tryptophanase, and the three tricarboxylic acid cycle enzymes, were also released from catabolite repression. Both mutants had sevenfold the aspartase formation of the wild-type strain in a medium which contained fumaric acid as the main carbon source and which has been used for industrial production of E. coli B aspartase. However, strain EAPc244 had 2.5-fold the fumarase activity of strain EAPc7.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aspartase-hyperproducing mutants of Escherichia coli B

When a wild-type strain of Escherichia coli B was cultured on a medium containing L-aspartic acid as the sole carbon source (Asp-C medium), aspartase formation was higher than that observed in minimal medium. Addition of glucose to Asp-C medium decreased aspartase formation. When also cultured in a medium containing L-aspartic acid as the sole nitrogen source (Asp-N medium), E. coli B showed a low level of aspartase formation and an elongated doubling time. To obtain aspartase-hyperproducing strains, we enriched cells growing faster than cells of the wild-type strain in Asp-N medium by continuous cultivation of mutagenized cells. After plate selection, the doubling times of these mutants were measured. Thereafter, fast-growing mutants were tested for aspartase formation. One of these mutants, strain EAPc7, had a higher level of aspartase formation than did the wild-type strain in medium containing L-aspartic acid as the carbon source, however; addition of glucose to this medium decreased aspartase formation. The other mutant, strain EAPc244, had a higher level of aspartase activity than did the wild-type strain in both media. Therefore, aspartase formation in mutant EAPc244 was released from catabolite repression. In strain EAPc244 the other catabolite-repressible enzymes, beta-galactosidase, tryptophanase, and the three tricarboxylic acid cycle enzymes, were also released from catabolite repression. Both mutants had sevenfold the aspartase formation of the wild-type strain in a medium which contained fumaric acid as the main carbon source and which has been used for industrial production of E. coli B aspartase. However, strain EAPc244 had 2.5-fold the fumarase activity of strain EAPc7.(ABSTRACT TRUNCATED AT 250 WORDS)     

Subcellular localization and some properties of the adenylate cyclase activity of the yeast, Saccharomyces cerevisiae

Saccharomyces cerevisiae was grown in the presence of 5% (w.v) Glucose and converter to protoplasts. The total particulate material obtained from lysed protoplasts was fractionated by sucrose density gradient ultracentrifugation and the distribution of adenylate cyclase throughout the gradient determined. Adenylate cyclase activity was found to be larger associated whith intracellular particulate fractions. Little activity was found in the plasma membrane-rich fraction.The adenylate cyclase activity was found to be inhibited by F^?, pyrophosphate and aminophylline, whereas glucagon, 5-hydroxytryptamine and concanavalin A were without effect.The enzymic activity appeared to be modulated by “catabolite repressors” (glucose, fructose and α-methylglucoside) as well as by acetate. A possible role for adenylate cyclase in regulating the levels of cyclic AMP in the cell during glucose repression is suggested.     

R-Plasmid Transfer to and from Escherichia coli Strains Isolated from Human Fecal Samples

Strains of Escherichia coli recently isolated from human feces were examined for the frequency with which they accept an R factor (R1) from a derepressed fi⁺ strain of E. coli K-12 and transfer it to fecal and laboratory strains. Colicins produced by some of the isolates rapidly killed the other half of the mating pair; therefore, conjugation was conducted by a membrane filtration procedure whereby this effect was minimized. The majority of fecal E. coli isolates accepted the R factor at lower frequencies than K-12 F⁻, varying from 10⁻² per donor cell to undetectable levels. The frequencies with which certain fecal recipients received the R-plasmid were increased when its R⁺ transconjugant was either cured of the R1-plasmid and remated with the fi⁺ strain or backcrossed into the parental strain. The former suggests the loss of an incompatibility plasmid, and the latter suggests the modification of the R1-plasmid deoxyribonucleic acid (DNA). In general, the fecal R⁺E. coli transconjugants were less effective donors for K-12 F⁻ and heterologous fecal strains than was the fi⁺ K-12 strain, whereas the single strain of Citrobacter freundii examined was generally more competent. Passage of the R1-plasmid to strains of salmonellae reached mating frequencies of 10⁻¹ per donor cell when the recipient was a Salmonella typhi previously cured of its resident R-plasmid. However, two recently isolated strains of Salmonella accepted the R1-plasmid from E. coli K-12 R⁺ or the R⁺E. coli transconjugants at frequencies of 5 × 10⁻⁷ or less.     

The Escherichia coli adenylate cyclase complex. Regulation by enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system.

The activity of adenylate cyclase of Escherichia coli measured in toluene-treated cells under standard conditions is subject to control by the phosphoenolpyruvate:sugar phosphotransferase system (PTS). Sugars such as glucose, which are transported by the PTS, will inhibit adenylate cyclase provided the PTS is functional. An analysis was made of the properties of E. coli strains carrying mutations in PTS proteins. Leaky mutants in the PTS protein HPr are similar to wild-type strains with respect to cAMp regulation; adenylate cyclase activity in toluene-treated cells and intracellular cAMP levels are in the normal range. Furthermore, adenylate cyclase in toluene-treated cells of leaky HPr mutants is inhibited by glucose. In contrast, mutations in the PTS protein Enzyme I result in abnormalities in cAMP regulation. Enzyme I mutants generally have low intracellular cAMP levels. Leaky Enzyme I mutants show an unusual phosphoenolpyruvate-dependent activation of adenylate cyclase that is not seen in Enzyme I⁺ revertants or in Enzyme I deletions. A leaky Enzyme I mutant exhibits changes in the temperature-activity profile for adenylate cyclase, indicating that adenylate cyclase activity is controlled by Enzyme I. Temperature-shift studies suggest a functional complex between adenylate cyclase and a regulator protein at 30 °C that can be reversibly dissociated at 40 °C. These studies further support the model for adenylate cyclase activation that involves phosphoenolpyruvate-dependent phosphorylation of a PTS protein complexed to adenylate cyclase.     

Regulation of plasmid-encoded lactose genes in different gram-negative enterobacteriaceae

The expression and regulation of a variety of plasmid-encoded lactose systems have been studied in different gram-negative Enterobacteriaceae (Escherichia coli K-12, Serratia marcescens, and Enterobacter liquefaciens). They are similarly expressed in all strains, and they are inducible and sensitive to catabolite repression. Urea, known to bring about a specific catabolite repression effect, has been chosen to study some regulatory aspects of these plasmid-encoded lactose systems. We have shown that the expression of all lactose systems is inhibited by urea but the extent of the inhibition is strain dependent. This indicates that the genetic background of the host might modify in certain instances the expression of plasmid-encoded genes.     

Catabolite repression of the lac operon: effect of operator-constitutive mutations

Summary We have constructed and tested three lac diploid strains in an attempt to show whether operator-constitutive mutations relieve catabolite repression of the lac operon. Each of these carries a different operator mutation on the chromosome, and all three have the genotype I⁺P⁺O^cZ⁺Y^-polar/Flac I⁺P⁺O⁺Z^delY⁺A⁺. When these strains were grown in medium containing glucose plus gluconate, synthesis of -galactosidase (directed by a gene cis to a mutant operator) and of thiogalactoside transacetylase (directed by a gene cis to an intact operator) suffered equal catabolite repression. We conclude that the operator-constitutive mutations have no effect on catabolite repression. Since it has been shown in analogous experiments that all promoter mutations tested do alleviate catabolite repression, these results are consistent with the view that the operator and promoter are functionally distinct.     

Catabolite repression of β-galactosidase synthesis in Escherichia coli

1. Repression by glucose of β-galactosidase synthesis is spontaneously reversible in all strains of Escherichia coli examined long before the glucose has all been consumed. The extent of recovery and the time necessary for reversal differ among various strains. Other inducible enzymes show similar effects. 2. This transient effect of glucose repression is observed in constitutive (i⁻) and permease-less (y⁻) cells as well as in the corresponding i⁺ and y⁺ strains. 3. Repression is exerted by several rapidly metabolizable substrates (galactose, ribose and ribonucleosides) but not by non-metabolized or poorly metabolized compounds (2-deoxyglucose, 2-deoxyribose, phenyl thio-β-galactoside and 2-deoxyribonucleosides). 4. The transient repression with glucose is observed in inducible cells supplied with a powerful inducer of β-galactosidase synthesis (e.g. isopropyl thio-β-galactoside) but not with a weak inducer (lactose); in the latter instance glucose repression is permanent. Diauxic growth on glucose plus lactose can be abolished by including isopropyl thio-β-galactoside in the medium. 5. In some strains phosphate starvation increases catabolite repression; in others it relieves it. Adenine starvation in an adenine-requiring mutant also relieves catabolite repression by glycerol but not that by glucose. Restoration of phosphate or adenine to cells starved of these nutrients causes a pronounced temporary repression. Alkaline-phosphatase synthesis is not affected by the availability of adenine. 6. During periods of transient repression of induced enzyme synthesis the differential rate of RNA synthesis, measured by labelled uracil incorporation in 2min. pulses, shows a temporary rise. 7. The differential rate of uracil incorporation into RNA falls during exponential growth of batch cultures of E. coli. This is equally true for uracil-requiring and non-requiring strains. The fall in the rate of incorporation has been shown to be due to a real fall in the rate of RNA synthesis. The significance of the changes in the rate of RNA synthesis is discussed. 8. A partial model of catabolite repression is presented with suggestions for determining the chemical identification of the catabolite co-repressor itself.     

The catalytic domain of Escherichia coli K-12 adenylate cyclase as revealed by deletion analysis of the cya gene

In Escherichia coli, adenylate cyclase activity is regulated by phosphorylated EnzymeIIA^Glc, a component of the phosphotransferase system for glucose transport. In strains deficient in EnzymeIIA^Glc, CAMP levels are very low. Adenylate cyclase containing the D414N substitution produces a low level of cAMP and it has been proposed that D414 may be involved in the process leading to activation by EnzymeIIA^Glc. In this work, spontaneous secondary mutants producing large amounts of cAMP in strains deficient in EnzymeIIA^Glc were obtained. The secondary mutations were all deletions located in the cya gene around the D414N mutation, generating adenylate cyclases truncated at the carboxyl end. Among them, a 48 kDa protein (half the size of wild-type adenylate cyclase) was shown to produce ten times more cAMP than wild-type adenylate cyclase in strains deficient in EnzymeIIA^Glc. In addition, this protein was not regulated in strains grown on glucose and diauxic growth was abolished. This allowed the definition of a catalytic domain that is not regulated by the phosphotransferase system and produces levels of cAMP similar to that of regulated wild-type adenylate cyclase in wild-type strains grown in the absence of glucose. Further analysis allowed the characterization of the COOH-terminal regulatory domain, which is proposed to be inhibitory to the activity of the catalytic domain.     

Inhibition of mouse brain synaptosomal gamma-aminobutyric acid transport by pyridoxal 5'-phosphate

Crude lysates from a strain of enterotoxigenic $\text{E. coli}$ have been shown to catalyse the incorporation of [³²P] from [adenylate-³²P] NAD⁺ into an 11,000 dalton protein in rat liver membranes. [³²P] incorporation paralleled adenylate cyclase activation and the results suggest that the mechanism of action of the heat-labile $\text{E. coli}$ enterotoxin may involve ADP-ribosylation of an intracellular acceptor protein.     

Fermentative production of dipicolinic acid by Penicilium citreoviride from sugarcane molasses

In Penicillium citreoviride strain 3114, dipicolinic acid (DPA) synthesis is inhibited by Ca⁺⁺ ions and susceptible to catabolite repression, making it unsuitable for fermentation in sugarcane molasses. A mutant, 27133-dpa-Ca-14, was derived through stepwise mutation and selection to produce DPA in the presence of 1000 ppm Ca⁺⁺ and also to be resistant to catabolite repression. With this mutant, higher product concentrations (36 g DPA/l) could be reached without prior removal of Ca⁺⁺ from the molasses. The DPA yields increased by about four times (0.4 g DPA/g glucose consumed) and productivity by two and a half-times (3.0 g DPA/l.d) compared with that of the parent strain 3114. Higher product yields (0.58–0.59 g DPA/g glucose consumed) were obtained in a multiple stage fermentation system. DPA was recovered through sepration by ion exchange chromatography followed by concentration and crystallization.     

Acetohydroxy acid synthase isoenzymes of Escherichia coli K-12: A trans-acting regulatory locus for ilvHI gene expression

Summary We isolated an Escherichia coli K-12 regulatory mutation affecting the acetohydroxy acid synthase III isoenzyme. This mutation was found to lie outside the structural genes ilvHI for this isoenzyme and was designated lrs-1. A strain carrying this mutation was found to be altered in the leucine-mediated control of ilvHI mRNA and acetohydroxy acid synthase III synthesis observed in the isogenic lrs ⁺ strain. These alterations appeared to be a consequence of a reduced intracellular concentration of a single one of five tRNA^Leu isoaccepting species.     

Modified nucleosides and the chromatographic and aminoacylation behavior of tRNAIle from Escherichia coli C6

Transfer RNA from Escherichia coli C6, a Met⁻, Cys⁻, relA⁻ mutant, was previously shown to contain an altered tRNA^Ile which accumulates during cysteine starvation (Harris, C.L., Lui, L., Sakallah, S. and DeVore, R. (1983) J. Biol. Chem. 258, 7676–7683). We now report the purification of this altered tRNA^Ile and a comparison of its aminoacylation and chromatographic behavior and modified nucleoside content to that of tRNA^Ile purified from cells of the same strain grown in the presence of cysteine. Sulfur-deficient tRNA^Ile (from cysteine-starved cells) was found to have a 5-fold increased V_max in aminoacylation compared to the normal isoacceptor. However, rates or extents of transfer of isoleucine from the [isoleucyl ∼ AMP · Ile-tRNA synthetase] complex were identical with these two tRNAs. Nitrocellulose binding studies suggested that the sulfur-deficient tRNA^Ile bound more efficiently to its synthetase compared to normal tRNA^Ile. Modified nucleoside analysis showed that these tRNAs contained identical amounts of all modified bases except for dihydrouridine and 4-thiouridine. Normal tRNA^Ile contains 1 mol 4-thiouridine and dihydrouridine per mol tRNA, while cysteine-starved tRNA^Ile contains 2 mol dihydrouridine per mol tRNA and is devoid of 4-thiouridine. Several lines of evidence are presented which show that 4-thiouridine can be removed or lost from normal tRNA^Ile without a change in aminoacylation properties. Further, tRNA isolated from E. coli C6 grown with glutathione instead of cysteine has a normal content of 4-thiouridine, but its tRNA^Ile has an increased rate of aminoacylation. We conclude that the low content of dihydrouridine in tRNA^Ile from E. coli cells grown in cysteine-containing medium is most likely responsible for the slow aminoacylation kinetics observed with this tRNA. The possibility that specific dihydrouridine residues in this tRNA might be necessary in establishing the correct conformation of tRNA^Ile for aminoacylation is discussed.     

Catabolite repression in Escherichia coli mutants lacking cyclic AMP.

Summary The regulation of catabolite repression of -galactosidase has been studied in Escherichia coli mutants deleted for the adenyl cyclase gene (cya ), and thus unable to synthesize cyclic AMP. It has been found that, provided a second mutation occurs either in the crp gene coding for the catabolite gene activator protein (CAP) or in the Lactose region, these mutants exhibit catabolite repression. If the catabolite repression seen in the mutant strains corresponds to the mechanism operating in wild-type cells, the results would suggest that the intracellular concentration of cyclic AMP cannot be the unique regulator of catabolite repression.Jacques Monod was still with us when most of the work described in this and the following paper was accomplished. His constant interest, his unfailing advice, his warm support, were invaluable. It will be difficult for us to ever enjoy a successful experiment without regretting that he cannot share this pleasure with us.     

Characterization of an aspartate-dependent acid survival system in Yersinia pseudotuberculosis

Enteric bacteria have developed various survival systems that protect against acid stress. In this study, an aspartate-dependent acid survival system is characterized in Yersinia pseudotuberculosis. The expression of aspartase (AspA) was confirmed to be increased at acidic pH by proteomic and lacZ fusion analyses. Addition of aspartate increased acid survival of the wild type but not the aspA knockout mutant. AspA increases acid survival by producing ammonia as demonstrated by mutation and in vitro enzyme activity analyses. This is the first demonstration that an enzyme involved in aspartate metabolism plays a role in acid survival in an enteric bacterium.