Further evidence for positive control of the L-arabinose system by gene araC

Mutations affecting catabolite repression of the L-arabinose regulon in Escherichia coli B/r

Expression of the L-arabinose regulon in Escherichia coli B/r requires, among other things, cyclic adenosine-3', 5'-monophosphate (cAMP) and the cAMP receptor protein (CRP). Mutants deficient in adenyl cyclase (cya-), the enzyme which synthesizes cAMP, or CRP (crp-) are unable to utilize a variety of carbohydrates, including L-arabinose. Ara+ revertants of a cya-crp- strain were isolated on 0.2% minimal L-arabinose plates, conditions which require the entire ara regulon to be activated in the absence of cAMP and CRP. Evidence from genetic and physiological studies is consistent with placing these mutations in the araC regulatory gene. Deletion mapping with one mutant localized the site within either araO or araC, and complementation tests indicated the mutants acted trans to confer the ability to utilize L-arabinose in a cya-crp- genetic background. Since genetic analysis supports the conclusion, that the mutant sites are in the araC regulatory gene, the mutants were designated araCi, indicating a mutation in the regulatory gene affecting the cAMP-CRP requirement. Physiological analysis of one mutant, araCi1, illustrates the trans-acting nature of the mutation. In a cya-crp- genetic background, araCi1 promoted synthesis of both isomerase, a product of the araBAD operon, and permease, a product of the araE operon. Isomerase and permease levels in araCi1 cya+ crp+ were hyperinducible, and the sensitivity of each to cAMP was altered. Two models are presented that show the possible mutational lesion in the araCi strains.

Electron microscopy of gene regulation: the L-arabinose operon

Unlike normal cells, malignant rat and two simian virus 40-transformed human cell lines can neither grow nor survive in B12- and folate-supplemented media in which methionine is replaced by homocysteine. Yet three lines of evidence indicate that the malignant and transformed cells synthesize large amounts of methionine endogenously through the reaction catalyzed by 5-methyltetrahydropterolyl-L-glutamate: L-homocysteine S-methyltransferase (EC 2.1.1.13). (1) The activities of this methyltransferase were comparable in extracts of malignant and normal cells. (2) The uptake of radioactive label from [5-14C]methyltetrahydropteroyl-L-glutamic acid (5-Me-H4PteGlu) was at least as great in the malignant cells as in the normals and was nearly totally dependent on the addition of homocysteine, the methyl acceptor; furthermore, 59-84% of the label incorporated by cells was recovered as methionine.

Isolation of specialized transducing bacteriophage lambda carrying genes of the L-arabinose operon of Escherichia coli B/r

A heat-inducible lysis-defective phage lambda (lambdacI857S7) has been integrated at multiple sites within the L-arabinose region (araCOIBAD) of a strain of Escherichia coli K-12 deleted for the normal lambda attachment site (lambdaattdelta). The lambda phage has become integrated with opposite orientations at two different loci within the aratb gene and with the "normal" orientation (clockwise N-RA-J) at a single site in the araC gene. The burst size, spontaneous-curing frequencies, and number of prophage harbored by each of the ara secondary-site lysogens have been determined. From these secondary-site lysogens it has been possible to generate plaque-forming ara-transducing phage (lambdapara) and defective ara-transducing phage (lambdadara), as well as defective leucine-transducing particles (lambdadleu). The construction and characterization of these lambdaara-transducing phage and their derivatives which carry genetically defined portions of the L-arabinose region are presented.

Enzymatic adaptation by bacteria under pressure

A study of enzymic adaptation under hydrostatic pressure by moderately barotolerant bacteria that can grow at pressure up to about 500 atm revealed that some adaptive processes are relatively insensitive to pressure, whereas others are sufficiently barosensitive to compromise survival capacity in situations requiring adaptation to new substrates under pressure. Examples of the former include adaptation of Escherichia coli to arabinose catabolism for growth and adaptation of Streptococcus faecalis to catabolism of lactose, ribose, or maltose. Examples of the latter include derepression of the lac operon in Escherichia coli and induction of penicillinase synthesis by Bacillus licheniformis. For both these barosensitive systems, pressure had little effect on enzyme levels in constitutive strains or in bacteria that had previously been induced at 1 atm. Moreover, it had no detectable effect on penicillinase secretion. However, pressures of 300 to 400 atm were found to reduce markedly rates and extents of enzyme synthesis by bacteria undergoing derepression or adaptation. This inhibitory effect of pressure was reflected in greater barosensitivity with extended lag and slower growth of initially unadapted Escherichia coli cells inoculated into minimal medium with lactose as sole source of carbon and fuel, and by major reductions in the minimal inhibitory concentrations of penicillin G for unadapted B. licheniformis cells inoculated into complex, antibiotic-containing media. Cyclic adenosine 5'-monophosphate did not reverse pressure inhibition of derepression of the lac operon, and catabolite repression was complete under pressure. However, derepression of the lac operon was more sensitive to pressure at low concentrations of inducer than at high concentrations. Apparent volume changes for derepression were 94 and 60 ml/mol at inducer concentrations of about 0.5 and 5 mM, respectively. Pressure was found not to be inhibitory for uptake of beta-galactosides; in fact, it was somewhat stimulatory. Therefore, results were interpreted in terms of inducer binding and subsequent conversion of an operator-inducer-repressor complex to inactive repressor and operator. Both reactions appeared to result in an increase in volume, the former more so than the latter. We found also that 200 atm was actually stimulatory for growth of Escherichia coli in minimal media, and the bacterium was in a sense barophilic.

In vitro activation of the transcription of araBAD operon by araC activator

The transcription of araBAD operon requires araC activator and cyclic AMP. D-Fucose inhibits ara mRNA synthesis. Our results indicate that the positive control by araC activator is exerted at the level of transcription.

Mutations in the L-arabinose operon of Escherichia coli B-r that result in hypersensitivity to catabolite repression

Two independent mutants resistant to l-arabinose inhibition only in the presence of d-glucose were isolated from an l-arabinose-sensitive strain containing the araD139 mutation. Preliminary mapping studies indicate that these mutations are closely linked to the araIOC region. Addition of d-glucose to growing cultures of these mutants results in a 95 to 98% repression of ara operon expression, as compared to a 50% repression of the parental control. Since cultures of both mutant and parental strains undergo a 50% repression of lac operon expression upon addition of glucose, the hypersensitivity to catabolite repression exhibited by these mutants is specific for the ara operon. Addition of cyclic adenosine monophosphate reverses the catabolite repression of the ara operon in both mutant and parent strains to 70 to 80% of the control. It is suggested that in these mutants the affinity of the ara operon initiator region for the cAMP-catabolite-activator protein complex may have been altered.

Genetic analysis of the leucine region in Escherichia coli B-r: gene-enzyme assignments

Genetic mapping by transduction and conjugation using F(-) and F' strains carrying either point mutations in the l-arabinose or leucine regions or ara-leu fusion-deletion mutations has resulted in a detailed genetic map of the arabinose-leucine region of Escherichia coli B/r. These studies have identified four genes in the leucine region having the same order as found in Salmonella typhimurium: ara... leuDCBA.

Novel mutation to dominant fucose resistance in the L-arabinose operon of Escherichia coli

We isolated an unusual mutant in which the arabinose operon carried an araC lesion that led to a dominant fucose resistance while retaining recessive constitutivity. All previously characterized C(c) mutations have been recessive for both fucose resistance and constitutivity.

Requirement of adenosine-3',5'-cyclic monophosphate for L-arabinose isomerase synthesis in Escherichia coli

Adenosine-3', 5'-cyclic monophosphate (cyclic AMP) is essential for the synthesis of l-arabinose isomerase in Escherichia coli. Cyclic AMP appears to be required for the transcription of deoxyribonucleic acid into messenger ribonucleic acid (RNA), since the enzyme synthesis is not observed in induced cells to which cyclic AMP is added after messenger RNA synthesis is arrested by rifampin or after inducer removal.

Genetic analysis of flagellar mutants in Escherichia coli

Flagellar mutants in Escherichia coli were obtained by selection for resistance to the flagellotropic phage chi. F elements covering various regions of the E. coli genome were then constructed, and, on the basis of the ability of these elements to restore flagellar function, the mutations were assigned to three regions of the E. coli chromosome. Region I is between trp and gal; region II is between uvrC and aroD; and region III is between his and uvrC. F elements carrying flagellar mutations were constructed. Stable merodiploid strains with a flagellar defect on the exogenote and another on the endogenote were then prepared. These merodiploids yielded information on the complementation behavior of mutations in a given region. Region III was shown to include at least six cistrons, A, B, C, D, E, and F. Region II was shown to include at least four cistrons, G, H, I, and J. Examination of the phenotypes of the mutants revealed that those with lesions in cistron E of region III produce "polyhooks" and lesions in cistron F of region III result in loss of ability to produce flagellin. Mutants with lesions in cistron J of region II were entirely paralyzed (mot) mutants. Genetic analysis of flagellar mutations in region III suggested that the mutations located in cistrons A, B, C, and E are closely linked and mutations in cistrons D and F are closely linked.

L-arabinose isomerase formation in a conditional mutant of gene araA of Escherichia coli B-r

A temperature-sensitive mutant of Escherichia coli in which the synthesis of l-arabinose isomerase is blocked during growth at 42 C was found to possess the following properties. (i) The mutation occurred in the structural gene for the isomerase, gene araA. (ii) During growth at elevated temperatures the mutant accumulates a product which is a precursor to the active enzyme. (iii) The precursor produced at 42 C is slowly converted to active enzyme at 28 C in the absence of protein and ribonucleic acid synthesis. It is concluded that the mutation results in a change in the structure of isomerase which causes formation of active enzyme to be thermolabile at a step beyond the level of translation.

Fine-structure deletion map of the Escherichia coli L-arabinose operon

A fine-structure deletion map of the L-arabinose operon of E. coli was constructed by mapping deletion endpoints against point mutations. Of 350 independent deletions with average endpoint separation of ten nucleotides, 51 ended in the control region between the C and B genes, and the rest ended in the structural genes A, B, C, and D. If deletion endpoints are randomly distributed, the C and B genes are separated by about 510 nucleotides. Deletion endpoints and locations of point mutations in fact do appear randomly interspersed in the C and B genes, but no point mutations were found in the control region between them. Deletions were isolated with the aid of a heat-inducible lambda phage inserted into leucine genes adjacent to the arabinose genes. A high-capacity mating technique was developed for rapidly generating fine structure maps from many deletions and point mutations.

Evidence against the presence of 3',5'-cyclic adenosine monophosphate and relevant enzymes in Lactobacillus plantarum

Analysis of cells of Lactobacillus plantarum, starved or undergoing induction, showed no 3', 5'-cyclic adenosine monophosphate (cAMP). Neither adenyl cyclase nor 3', 5'-cAMP phosphodiesterase was detected in extracts. Extracts of L. plantarum did not inhibit these two enzymes of Escherichia coli K-12, strain W1435. Incubation of adenosine triphosphate (ATP)-U-(14)C with cells or various cell-free fractions of L. plantarum did not produce labeled 3', 5'-cAMP. Of various 3', 5'-cyclic and acyclic nucleotides tested, only 3', 5'-cAMP, ATP, and yeast adenylic acid stimulated l-arabinose isomerase. Yeast adenylic acid was two to four times as effective as 3', 5'-cAMP or ATP. 2', 3'-cAMP was not effective.

A second transport system for L-arabinose in Escherichia coli B-r controlled by the araC gene

Escherichia coli B/r possesses two active transport systems for l-arabinose, both of which are regulated by araC, the regulatory gene for the l-arabinose operon. The system with the higher affinity for l-arabinose has a K(m) for initial uptake of l-arabinose of 8.3 x 10(-6)m; the system of lower affinity has a K(m) of 1.0 x 10(-4)m. The two systems can also be distinguished by differences in their response to analogues that act as competitive inhibitors of initial uptake. d-Galactose strongly inhibits l-arabinose uptake by the high affinity system but only weakly inhibits such uptake by the low affinity system. d-Fucose, d-xylose, and beta-methyl-l-arabinoside competitively inhibit the uptake of l-arabinose by both systems to approximately the same extent. d-Glucose and l-lyxose do not inhibit either system. On the basis of kinetic evidence and the properties of mutants lacking one or the other of the two systems, it has been concluded that the high affinity uptake system involves the l-arabinose binding protein. Kinetic studies have shown that the K(m) for l-arabinose uptake by the high affinity system resembles the K(m) for binding of l-arabinose by the binding protein, and both have similar K(i) values for the inhibitory substrates tested. A consideration of l-arabinose transport-deficient mutants has demonstrated that the previously described araE mutants lack the low affinity system but retain the high affinity system and have normal levels of the l-arabinose binding protein. Mutants described in this communication which lack only the high affinity system either contain no detectable l-arabinose binding protein or possess an immunologically cross-reacting material that is reduced in its ability to bind l-arabinose. These observations support a role for the binding protein in l-arabinose uptake.

Characterization of strong polar mutations in a region immediately adjacent to the L-arabinose operator in Escherichia coli B-r

Seven l-arabinose-negative mutations are described that map in three genetically distinct regions immediately adjacent to the araO (operator) region of the l-arabinose operon. All seven mutants revert spontaneously, exhibit a cis-dominant, trans-recessive polarity effect upon the expression of l-arabinose isomerase (gene araA), and fail to respond to amber, ochre, or UGA suppressors. Three of these mutants exhibit absolute polarity and are not reverted by the mutangens 2-aminopurine, diethyl sulfate, and ICR-191. These may have arisen as a consequence of an insertion mutation in gene araB or in the initiator region of the l-arabinose operon. The four remaining mutants exhibit strong but not absolute polarity on gene araA and respond to the mutagens diethyl sulfate and ICR-191. Three of these mutants are suppressible by two independently isolated suppressors that fail to suppress known nonsense codons. Partially polar Ara(+) revertants with lesions linked to ara are obtained from three of the same four mutants. These polar mutants, their external suppressors, and their partially polar revertants are discussed in terms of the mechanism of initiation of expression of the l-arabinose operon.

New amino acid regulatory locus having unusual properties in heterozygous merodiploids

Spontaneous mutants of Escherichia coli B/r resistant to 5',5',5',-trifluoro-dl-leucine contain defects in a gene which maps to the left of the threonine region. Low-level constitutive expression of the isoleucine-valine and leucine operons is caused by this mutation in haploid strains. This is in contrast to extremely high levels of gene expression in the heterozygous merodiploids (F' wild type/mutant allele). The properties of these mutants define a new locus and suggest that it encodes a subunit protein which is involved in the repression of the structural genes for the branched-chain amino acid pathways.

Induction of the ara operon of Escherichia coli B-r

The inducer specificity and kinetics of induction of the ara operon were examined in Escherichia coli B/r. A difference in the kinetics of induction was found between our B/r strains and the K-12 strain previously described by Schleif. The roles of active transport and metabolism of inducer, and of cell density, in induction were studied. d-Fucose and beta-methyl-l-arabinoside were competitive inhibitors of induction. No inducer of the wild-type strain other than l-arabinose was found. However, a procedure for selecting mutants with altered inducer affinity or specificity was developed. The properties of one such mutant (inducible by d-fucose) are described.

Genetic control of enzyme induction in the -ketoadipate pathway of Pseudomonas putida: deletion mapping of cat mutations

A number of spontaneous mutant strains of Pseudomonas putida, obtained by repeated selection for inability to grow with cis,cis-muconate, have been shown to carry deletions in catB, the structural gene for muconate lactonizing enzyme. These strains have been employed for deletion mapping of the genetic region containing catB and catC (the structural gene for muconolactone isomerase, the synthesis of which is coordinate with that of muconate lactonizing enzyme). All deletions that overlap mutant sites located on the left side of the genetic map, as well as the point mutations in that region, lead to a pleiotropic loss of both catB and catC activities. We propose that this region to the left of catB has a regulatory function. Although the details of regulation at the molecular level are unclear, our data indicate that catB and catC may well be controlled by a mechanism unlike any yet described by workers on enteric bacteria.

Deoxyribonucleic acid-ribonucleic acid hybridization studies on the L-Arabinose operon of Escherichia coli B-r

An increase in the rate of synthesis of ara-specific messenger ribonucleic acid as measured by deoxyribonucleic acid-ribonucleic acid hybridization has been detected in the induced wild-type (ara(+)) strain of Escherichia coli B/r as compared with the uninduced control, thus providing evidence that regulation of the positively controlled l-arabinose operon is at the level of transcription.

Purification of the araC protein

The araC gene product, a regulatory protein required for expression of the L-arabinose operon, has been purified by affinity chromatography on Sepharose 4B to which 4-aminophenyl-beta-D-6-deoxygalactopyranoside (an anti-inducer of the L-arabinose operon) had been covalently attached by means of a 4-aminophenylbutanamido side chain. Evidence is presented showing that the protein binds specifically to ara DNA.

Hyperinducibility as a result of mutation in structural genes and self-catabolite repression in the ara operon

Mutations in gene araB producing an l-arabinose-negative phenotype cause either an increase (hyperinducible), decrease (polar), or have no effect at all on the inducible rate of expression of the l-arabinose operon. Fourteen araB gene mutants exhibiting such effects were shown to be the result of: nonsense, frameshift, or missense mutations. All missense mutants were hyperinducible, exhibiting approximately a twofold increase in rate of l-arabinose isomerase production. All frameshift and most nonsense mutants exhibited polar effect. One nonsense mutant was hyperinducible. The cis-dominant polar effect of nonsense and frameshift mutants (as compared to induced wild type) were more pronounced in arabinose-utilizing merodiploids and in araBaraC(c) double mutants where inducible and constitutive enzyme levels are respectively determined. On the other hand, in arabinose-utilizing merodiploids, missense mutations no longer exhibited hyperinducibility but displayed a wild-type level of operon expression. Increases in the wild type-inducible rate of expression of the operon were found when growth rate was dependent on the concentration of l-arabinose. Cyclic 3',5'-adenosine monophosphate also stimulated expression of the operon with the wild type in a mineral l-arabinose medium. These observations are explained on the basis that the steady-state expression of the l-arabinose operon OIBAD is dependent on the concentration of (i) l-arabinose, the effector of this system, which stimulates the expression of the operon, and (ii) catabolite repressors, produced from l-arabinose, which dampen the expression of the operon. We have termed the latter phenomenon "self-catabolite" repression.

D-Fucose as a gratuitous inducer of the L-arabinose operon in strains of Escherichia coli B-r mutant in gene araC

d-Fucose, a nonmetabolizable analogue of l-arabinose, prevents growth of Escherichia coli B/r on a mineral salts medium plus l-arabinose by inhibiting induction of the l-arabinose operon. Mutations giving rise to d-fucose resistance map in gene araC and result in constitutive expression of the l-arabinose operon. Most of these mutations also permit d-fucose to serve as a gratuitous inducer. It is concluded that d-fucose-resistant mutants produce an araC gene product with an altered inducer specificity. Addition of l-arabinose to cells induced with the gratuitous inducer, d-fucose, resulted in severe transient repression of operon expression followed by permanent catabolite repression. Transient repression but no permanent catabolite repression was obtained when cells unable to metabolize l-arabinose were employed. It is concluded that transport of l-arabinose alone is sufficient to achieve transient repression of its own operon, but that metabolism of l-arabinose must occur to achieve permanent catabolite repression of the l-arabinose operon. This general effect has been termed "self-catabolite repression."

Induction and repression of L-arabinose isomerase in Salmonella typhimurium

As with other inducible enzymes, the induced synthesis of l-arabinose isomerase (l-arabinose ketol isomerase, EC 5.3.1.4) in Salmonella typhimurium is subject to catabolite repression. Of the three catabolite repressors tested, glucose produces maximum repression. Analogues of catabolite repressors like 2-deoxy-d-glucose and d-fucose also inhibit the synthesis of the enzyme. The catabolite repression is completely reversed in the presence of 1.5 x 10(-3)m cyclic 3',5'-adenosine monophosphate (AMP). The maximum repression is produced in glucose-grown cells in glucose-containing induction medium. Cyclic 3',5-AMP reverses this repression provided that the cells are treated with ethylenediaminetetraacetic acid (EDTA). In normal cells, cyclic 3',5'-AMP has no effect on the induction but in EDTA-treated cells the cyclic nucleotide enhances synthesis of the enzyme. The inhibition produced by d-fucose cannot be reversed by cyclic 3',5'-AMP. d-Fucose competes with the inducer l-arabinose in some step(s) involved in the process of induction.

"In vivo" detection of L-arabinose-binding protein, CRM-negative mutants

An "in vivo" assay for the detection of mutants negative to CRM (cross-reacting material) is described. l-Arabinose-negative mutants of Escherichia coli B/r were grown on Casamino Acids-l-arabinose plates to which a 3-ml agar layer, containing antiserum to the l-arabinose-binding protein (ABP), had been applied. After incubation and partial lysis of the clones "in situ," the plates were refrigerated for 36 hr, rinsed of colonial growth with water, and observed for the presence or absence of an immune precipitation. ABP-minus and l-arabinose regulator (araC)-minus mutants do not produce a precipitin reaction. l-Arabinose isomeraseless (EC 5.3.1.4; araA), kinaseless (EC 2.7.1.16; araB), and epimeraseless (EC 5.1.3.a; araD) mutants produce precipitin reactions. Mutants of E. coli B/r generated by treatment of the wild type with ethyl methane sulfonate or ultraviolet irradiation were isolated, tested for l-arabinose uptake, and screened for the presence or absence of ABP by the described assay. The applications of such an assay are discussed.

Control of expression of the L-arabinose operon in temperature-sensitive mutants of gene araC in Escherichia coli B-r

Expression of the l-arabinose operon in Escherichia coli B/r is dependent on the temperature of growth of the araC mutants reported in this paper. Analysis of these temperature-sensitive regulatory mutants indicates that both repressor and activator activities are thermolabile. The simplest model to explain the manner in which the operon is controlled is one suggesting that the regulatory gene, araC, codes for a protein which upon synthesis acts as a repressor molecule and prevents operon function. When inducer is added, the repressor undergoes a conformational shift and becomes an activator which switches on enzyme synthesis, provided the repressor concentration is reduced to a sufficiently low level in the cell. These data lend strong support to the model that both activities are the result of the same gene product.

Selection of araB and araC mutants of Escherichia coli B-r by resistance to ribitol

The growth of strain araC(c)67, which produces the enzymes of the ara operon constitutively, is inhibited by the addition of ribitol. Isolation of strains resistant to ribitol yields mutants of either the araB or araC genes. A model to account for the inhibition by ribitol is discussed.