Regulation of β-Galactosidase Synthesis in Escherichia coli by Cyclic Adenosine 3′,5′-Monophosphate

Inducer exclusion, by itself, cannot account for the glucose-mediated lac repression of Escherichia coli

The lac operon of Escherichia coli is repressed several 100-fold in the presence of glucose. This repression has been attributed to cAMP receptor protein-mediated inhibition of lac transcription and EIIA^Glc-mediated inhibition of lactose transport (inducer exclusion). The growing evidence against the first mechanism has led to the postulate that the repression is driven by inducer exclusion. Although inducer exclusion reduces the permease activity only 2-fold in fully induced cells, it could be more potent in partially induced cells. Here, we show that even in partially induced cells, inducer exclusion reduces the permease activity no more than 6-fold. Moreover, the repression is so small because these experiments are performed in the presence of chloramphenicol. Indeed, when glucose is added to a culture growing on glycerol and TMG, but no chloramphenicol, lac expression is repressed 900-fold. This repression is primarily due to reversal of the positive feedback loop, i.e., the decline of the intracellular TMG level leads to a lower permease level, which reduces the intracellular TMG level even further. The repression in the absence of chloramphenicol is therefore primarily due to positive feedback, which does not exist during measurements of inducer exclusion.

Quantitative effect and regulatory function of cyclic adenosine 5'-phosphate in Escherichia coli

Cyclic adenosine 5'-phosphate (cAMP) is a global regulator of gene expression in Escherichia coli. Despite decades of intensive study, the quantitative effect and regulatory function of cAMP remain the subjects of considerable debate. Here, we analyse the data in the literature to show that: (a) In carbon-limited cultures (including cultures limited by glucose), cAMP is at near-saturation levels with respect to expression of several catabolic promoters (including lac, ara and gal). It follows that cAMP receptor protein (CRP) cAMP-mediated regulation cannot account for the strong repression of these operons in the presence of glucose. (b) The cAMP levels in carbon-excess cultures are substantially lower than those observed in carbon-limited cultures under these conditions, the expression of catabolic promoters is very sensitive to variation of cAMP levels. (c)=CRPcAMP invariably activates the expression of catabolic promoters, but it appears to inhibit the expression of anabolic promoters. (d) These results suggest that the physiological function of cAMP is to maintain homeostatic energy levels. In carbon-limited cultures, growth is limited by the supply of energy; the cAMP levels therefore increase to enhance energy accumulation by activating the catabolic promoters and inhibiting the anabolic promoters. Conversely, in carbonexcess cultures, characterized by the availability of excess energy, the cAMP levels decrease in order to depress energy accumulation by inhibiting the catabolic promoters and activating the anabolic promoters.

Gene regulation in continuous cultures: a unified theory for bacteria and yeasts

During batch growth on mixtures of two growth-limiting substrates, microbes consume the substrates either sequentially (diauxie) or simultaneously. The ubiquity of these growth patterns suggests that they may be driven by a universal mechanism common to all microbial species. Recently, we showed that a minimal model accounting only for enzyme induction and dilution, the two processes that occur in all microbes, explains the phenotypes observed in batch cultures of various wild-type and mutant/recombinant cells (Narang and Pilyugin in J. Theor. Biol. 244:326-348, 2007). Here, we examine the extension of the minimal model to continuous cultures. We show that: (1) Several enzymatic trends, attributed entirely to cross-regulatory mechanisms, such as catabolite repression and inducer exclusion, can be quantitatively explained by enzyme dilution. (2) The bifurcation diagram of the minimal model for continuous cultures, which classifies the substrate consumption pattern at any given dilution rate and feed concentrations, provides a precise explanation for the empirically observed correlations between the growth patterns in batch and continuous cultures. (3) Numerical simulations of the model are in excellent agreement with the data. The model captures the variation of the steady state substrate concentrations, cell densities, and enzyme levels during the single- and mixed-substrate growth of bacteria and yeasts at various dilution rates and feed concentrations. This variation is well approximated by simple analytical expressions that furnish deep physical insights. (4) Since the minimal model describes the behavior of the cells in the absence of cross-regulatory mechanisms, it provides a rigorous framework for quantifying the effect of these mechanisms. We illustrate this by analyzing several data sets from the literature.

A deficiency in cyclic AMP results in pH-sensitive growth of Escherichia coli K-12

Mutants of Escherichia coli K-12 deficient in adenyl cyclase (cya) and catabolite activator protein (crp) have been shown to grow more slowly than their parent strains in glucose-minimal medium. Their growth rate decreased markedly with increasing pH between 6 and 7.8. We have shown that this pH sensitivity is a direct consequence of the cya mutation, because a mutation to pH resistance also restored ability to ferment a variety of sugars. The proton motive force-dependent uptake of proline and glutamate was also reduced and sensitive to pH in the cya mutant. The membrane-bound ATPase activity was normal. The rate of oxygen uptake by cells, although reduced, was pH insensitive. We suggest several explanations for this phenotype, including a possible defect in energy transduction.

Cyclic AMP levels during induction and repression of cellulase biosynthesis in Thermomonospora curvata

Specific cellulase production rates (SCPR) were compared with intracellular cyclic AMP (cAMP) levels in the thermophilic actinomycete, Thermomonospora curvata, during growth on several carbon sources in a chemically defined medium. SCPR and cAMP levels were 0.03 U (endoglucanase [EG] units) and 2 pmol per mg of dry cells, respectively, during exponential growth on glucose. These values increased to about 6 and 25, respectively, during growth on cellulose. Detectable EG production ceased when cAMP levels dropped below 10. Cellobiose (usually considered to be a cellulase inducer) caused a sharp decrease in cAMP levels and repressed EG production when added to cellulose-grown cultures. 2-deoxy-D-glucose, although nonmetabolizable in T. curvata, depressed cAMP to levels observed with glucose, but unlike glucose, the 2DG effect persisted until cells were washed and transferred to fresh medium. SCPR values and cAMP levels in cells grown in continuous culture under conditions of cellobiose limitation were markedly influenced by dilution rate (D). The maxima for both occurred at D = 0.085 (culture generation time of 11.8 h). When D was held constant and cellobiose concentration was increased over a 14-fold range to support higher steady state population levels, SCPR values decreased about fivefold, indicating that extracellular catabolite accumulation may be a factor in EG repression. The role of cAMP in the mechanism of this repression appears to be neither simple nor direct, since large changes (up to 200-fold) in SCPR accompany relatively small changes (10-fold) in cellular cAMP levels.

The effect of glucose on cellobiose uptake and beta-D-glucosidase activity in Streptomyces granaticolor

Glucose inhibits the inducible synthesis of beta-D-glucosidase in Streptomyces granaticolor. Neither cAMP nor cGMP influence the inhibitory effect of glucose. Glucose also inhibits the inducible synthesis of the cellobiose uptake system but has no effect on its activity. This may be the mechanism underlying glucose inhibition of induction of beta-D-glucosidase in S. granaticolor.

Role of catabolite regulatory mechanisms in control of carbohydrate utilization by the rumen anaerobic fungus Neocallimastix frontalis

Neocallimastix frontalis PN-1 utilized the soluble sugars D-glucose, D-cellobiose, D-fructose, maltose, sucrose, and D-xylose for growth. L-Arabinose, D-galactose, D-mannose, and D-xylitol did not support growth of the fungus. Paired substrate test systems were used to determine whether any two sugars were utilized simultaneously or sequentially. Of the paired monosaccharides tested, glucose was found to be preferentially utilized compared with fructose and xylose. The disaccharides cellobiose and sucrose were preferentially utilized compared with fructose and glucose, respectively, an cellobiose was also the preferred substrate compared with xylose. Xylose was the preferred substrate compared with maltose. In further incubations, the fungus was grown on the substrate utilized last in the two-substrate tests. After moderate growth was attained, the preferred substrate was added to the culture medium. Inhibition of nonpreferred substrate utilization by the addition of the preferred substrate was taken as evidence of catabolite regulation. For the various combinations of substrates tested, fructose and xylose utilization was found to be inhibited in the presence of glucose, indicating that catabolite regulation was involved. No clear-cut inhibition was observed with any of the other substrate combinations tested. The significance of these findings in relation to rumen microbial interactions and competitions is discussed.

Enzymatic and Microbial Preparation of d -Xylulose from d -Xylose

A high- d -xylulose mixture ( d -xylose- d -xylulose = 33:67) was prepared from the cold ethanol extract of preisomerized d -xylose solution ( d -xylose- d -xylulose = 77:23). Fusarium oxysporum f. sp. lini and Aspergillus niger were demonstrated to preferentially utilize d -xylose in the mixture of d -xylose and d -xylulose. Chromatographically pure d -xylulose was thus obtained in 90% yield. A high- d -xylulose mixture was also incubated with Rhodotorula toruloides, Klebsiella pneumoniae, Candida utilis , or Mucor rouxii. d -Xylose and d -xylulose were simultaneously consumed. When borate was added to the mixture, a d -xylulose-borate complex was formed, and it could be used to protect d -xylulose from being utilized.

Role of inducer exclusion in preferential utilization of glucose over melibiose in diauxic growth of Escherichia coli

The role of inducer exclusion in diauxic growth of Escherichia coli on glucose and melibiose was investigated. The amounts of glucose and melibiose in the culture medium were determined during the diauxie. Glucose was consumed during the first growth cycle of the diauxie, and melibiose was consumed during the second cycle. The addition of adenosine 3',5'-cyclic monophosphate to the culture medium released both transient and catabolite repressions on the melibiose operon by glucose. Biphasic growth without a transient lag phase was observed in the presence of adenosine 3',5'-cyclic monophosphate. Preferential utilization of glucose over melibiose was observed even under such conditions. Thus, it is clear that inducer exclusion alone is sufficient to ensure the preferential utilization of glucose over melibiose. Similar results were obtained from a glucose-lactose diauxie. Inducer exclusion itself was not affected by adenosine 3',5'-cyclic monophosphate.

Catabolite repression during single and multiple induction in Escherichia coli

Intracellular concentration of cAMP regulates the synthesis of enzymes sensitive to catabolite repression. The relationship between the single and multiple induction of beta-galactosidase (EC 3.2.1.23), L-tryptophanase (EC 4.1.99.1), D-serine deaminase (EC 4.2.1.14), L-asparaginase (EC 3.5.1.1) and L-malate dehydrogenase (EC 1.1.1.37) was studied and the effect of cAMP level on the induction in Escherichia coli Crookes (ATCC 8739) was investigated. A varying degree of catabolite repression was observed during induction of individual enzymes induced separately on different energy sources. The synthesis of l-tryptophanase was most sensitive, whereas l-asparaginase was not influenced at all. Exogenous cAMP was found to overcome partially the catabolite repression of beta-galactosidase and D-serine deaminase, both during single induction. The synthesis of l-malate dehydrogenase was negatively influenced by the multiple induction even in the presence of cAMP; on the other hand, the synthesis of l-tryptophanase was stimulated, independently of the level of the exogenous cAMP. Similarly, the activity of L-asparaginase slightly but significantly increased during the multiple induction of all five enzymes; here too the activity increase did not depend on exogenous cAMP.

"Self-catabolite repression" of pectate lyase in Erwinia carotovora

The induction of pectate lyase of Erwinia carotovora was repressed by a high concentration of its inducer. The concomitant addition of cyclic adenosine 3',5'-monophosphate reversed this repression.

Substrate Preferences in Rumen Bacteria: Evidence of Catabolite Regulatory Mechanisms

Five species of rumen bacteria with overlapping substrate fermentative capabilities were tested for substrate preferences and evidence of catabolite regulatory mechanisms. All five bacteria showed evidence of some type of catabolite regulatory mechanism. In the six-substrate test system that was used, utilization of every substrate was inhibited by another substrate in at least one of the bacteria. Inhibited versus noninhibited substrate data suggest that the five bacteria have different strategies of substrate utilization and thus occupy separate niches in the rumen. The significance of these observations to understanding the rumen ecosystem is discussed.

A mutation affecting the sigma subunit of RNA polymerase changes transcriptional specificity

The RNA polymerase mutation, alt-1, affects the sigma subunit and alters the in vitro selectivity of RNA polymerase to parallel the in vivo phenotype. We propose that the mutation changes the distribution of functionally distinct polymerase isomers.

Cyclic-AMP content in Escherichia coli B/b as affected by N1-(delta 2-isopentyl)adenine

N6-(delta 2-isopentenyl)adenine, like other cytokinins, does not detectably modify Escherichia coli growth, but strongly affects cellular levels of cAMP. A substantial delay of the highest level of intracellular cAMP, a reduction to about one half of such maximum level, and a slight increase of cAMP secreted into the medium are reported.

Influence of cyclic 3',5'-adenosine monophosphate on uracil uptake by rifampicin treated Escherichia coli cells

Incubation of cells from a wild type strain of E. coli with 0.3 mg/ml rifampicin for 15 minutes lead to a complete inhibition of RNA synthesis measured as the uracil incorporation into the trichloroacetic acid insoluble fraction. In these rifampicin-treated cells [14C]uracil incorporation tended to decrease during a further incubation at 37 degrees. Addition of cyclic AMP increased the inactivation of the system responsible for [14C]uracil uptake. The cyclic nucleotide effect seems to be specific since ATP or 5'AMP did not increase such inactivation.

Control of beta-glucosidase synthesis in Mucor racemosus

The beta-glucosidase of Mucor racemosus was shown to be synthesized when the organism was grown in the presence of such diverse carbon sources as glycerol, lactate, xylose, ribose, alpha-methylglucoside, alpha-phenylglucoside, maltose, and cellobiose. Enzyme synthesis was strongly repressed in the presence of hexoses. In addition, exogenous cyclic adenosine 3',5'-monophosphate (cAMP) resulted in enzyme repression. When cAMP was added exogenously after enzyme activity had accumulated, a reversible enzyme inactivation occurred. Growth on disaccharides (maltose or cellobiose) was severely retarded in the presence of cAMP, whereas that on glucose remained unaffected. The results indicate a probable role for cAMP in control of glucosidase synthesis in Mucor.

Cyclic AMP in dental and periodontal tissues during tooth eruption in kittens

Cyclic adenosine 3',5'-monophosphate (cAMP) concentrations and cellular distribution were studied in dental and periodontal tissues during tooth eruption in kittens. Although the mean levels of cAMP around developing teeth were similar in all the tissue samples, there were marked differences in cAMP stainability of tissues apical and occlusal to the erupting teeth.

Catabolite translational effects on the lac messenger RNA of Escherichia coli K12

The transcriptional and translational events occurring during the induction of the lac operon, were separated by blocking the translational step, either by aminoacid starvation or by addition of chloramphenicol. It was found that the carbon source used during the subsequent translation, affected the rate of beta-galactosidase synthesis. A decoordination effect on the production of enzymes of the lac system was also observed in high catabolite repression media, as well as in nitrogen limiting conditions. These findings suggested a similarity with the polarity phenomenon. In order to test this similarity, polarity suppressors of a Z- polar mutant were isolated. In one of these mutants, probably suA like, no carbon source effect was observed during the translational step. The induction kinetics in different media, after distinct pregrowth conditions, supported the idea that this mutant could be considered catabolite repression resistant only in certain restrictive conditions.

The site for catabolite deactivation in the L-arabinose BAD operon in Escherichia coli B/r

A series of deletions beginning in the leu operon and continuing into the araC gene and also into the ara controlling site region were analyzed in reciprocal merodiploids, e.g., F' A2Cc67/B24delta719, F' B24delta719/A2Cc67, for their effects on catabolite deactivation (CD). The results of these experiments are consistent with placing the catabolite gene activator-cyclic AMP sensitive site in the controlling site region between araB and araO. With a deletion mutant, delta1109, that places araBAD under leu control when transcription begins at leuP, the araBAD operon is immune to CD even though araCGA, araP and araI are intact and functional. To focus attention on the fine structure and related functions of this region we propose that the three proteins that function therein have separate sites of action: araI (initiator-site for activator), araP (promoter-site for RNA polymerase) and ara(CGA) (catabolite gene activator-site for CGA-cAMP). None of the eighteen initiator constitutive mutants (Ic) tested have any significant effect on catabolite derepression or on the maximal level of expression of the operon supporting the view that the araI site may be distinct from araP and ARA(CGA). A series of constitutive mutants in the araC gene (Cc) also have no pronounced effect on catabolite deactivation.

[Relations between catabolite repression and sporulation in Bacillus subtilis (author's transl)]

Acetoin dehydrogenase can be catabolite repressed by numerous sources of carbon. The following results point out that the catabolite repression of this enzyme and the inhibition of sporulation are mediated by the same mechanism: 1. Mutants, able to synthesize acetoin dehydrogenase in the presence of glucose, sporulate in glucose medium at a higher rate than the standard strain. 2. The catabolite repressing effect of a compound and its ability to inhibit sporulation are in a direct relation to each other. 3. The limitation of inorganic phosphate in the growth medium, which is known to favour sporulation, counteracts the catabolite repressing effect of glucose.

Regulation of uracil uptake in Escherichia coli by adenosine 3',5'-monophosphate

Culture of a wild-type strain of Escherichia coli in the presence of cyclic AMP leads to an impairment of uracil uptake. Half maximum inhibition of uracil uptake was observed at 1.5 mM cyclic AMP. The effect seems to be specific since no inhibition was found in cultures supplemented with ATP, ADP or 5'-AMP. Similarly the inhibition was not observed in cultures of a mutant deficient in the cyclic AMP receptor protein. The inhibition in uracil uptake, found in bacteria cultured in the presence of cyclic AMP, is not a consequence of a reduction in the growth rate. On the other hand, this inhibition was observed only in cultures containing glucose or pyruvate as carbon source.

Regulation of penicillin acylase in Escherichia coli by cyclic AMP

1. Cyclic AMP was found to stimulate penicillin acylase activity. 2. It also overcame the repression of glucose and restored enzyme synthesis to the non-repressed levels. 3. The conversion of inactive enzyme precursor into active enzyme was not stimulated by cyclic AMP in cells in which protein synthesis was inhibited by chloramphenicol. 4. Cyclic AMP failed to stimulate enzyme production in cells in which messenger RNA synthesis was arrested by rifampicin or inducer removal. 5. Cyclic AMP appears to participate in the regulation of this enzyme at the transcriptional level.

An adenosine 3',5'-monophosphate-requiring mutant of the luminous bacteria Beneckea harveyi

We have isolated a mutant of the luminous bacterium Beneckea harveyi, which requires exogenous adenosine 3',5'-monophosphate (cyclic AMP) to synthesize luciferase and emit light. The mutant was pleiotropic, lacking not only the ability to luminesce, but also the capacities to form flagella and the ability to utilize a variety of carbohydrates for growth. All these deficiencies could be corrected by added cyclic AMP. The cyclic AMP-induced de novo synthesis of luciferase was possible only after autoinduction had occurred. The induction time by cyclic AMP ranged between 6 and 10 min at 27 degrees C.

Transient repression of catabolite-sensitive enzyme synthesis elicited by 2,4-dinitrophenol

Transient inhibition of catabolic enzyme synthesis in Escherichia coli occurred when a low concentration of 2,4-dinitrophenol (DNP) was simultaneously added with inducer. Using mutant strains defective for gamma-gene product or constitutive for lac enzymes, it was found that the inhibition is not due to the exclusion of inducer by uncoupling. The addition of cyclic adenosine 3',5'-monophosphate overcame repression. The components of the lac operon coordinately responded to DNP inhibition. From deoxyribonucleic acid-ribonucleic acid hybridization experiments, it was found that the inhibition of beta-galactosidase induction occurred at the level of messenger ribonucleic acid synthesis specific for the lac operon. It seems probable that DNP represses induction in a similar manner to that of transient repression observed upon the addition of glucose. Furthermore, it was found that transient repression disappeared if cells were preincubated with DNP before induction. This indicates that new contact of cells with DNP is obligatory for transient repression. From these results, it is suggested that the cell membrane may be responsible for regulation of catabolite-sensitive enzyme synthesis.

Kinetics of the onset of catabolite repression in Escherichia coli as determined by lac messenger ribonucleic acid initiations and intracellular cyclic adenosine 3',5'-monophosphate levels

The rates of synthesis of beta-galactosidase (EC 3.2.1.23) and the intracellular levels of cyclic 3',5'-adenosine monophosphate (cAMP) soon after the addition of glucose or glycerol to exponentially growing cultures of Escherichia coli have been determined. Within 10 s of its addition, glucose, but not glycerol, lowered the apparent initiation frequency of lac messenger ribonucleic acid. The glucose-generated reduction in initiations is identified as catabolite repression by its reversibility with cAMP. The intracellular cAMP levels respond virtually identically to glucose and glycerol additions. Thus, no correlation was observed between the rate of messenger ribonucleic acid initiation and the level of cAMP.

Penicillinamidohydrolase in Escherichia coli. III. Catabolite repression, diauxie, effect of cAMP and nature of the enzyme induction

Synthesis of penicillinamidohydrolase (penicillin acylase, EC 3.5.1.11) in Escherichia coli is subjected to the absolute catabolite repression by glucose and partial repression by acetate. Both types of catabolite repression of synthesis of the enzyme in Escherichia coli are substantially influenced by cyclic 3',5'-adenosinemonophosphate (cAMP). Growth diauxie in a mixed medium containing glucose and phenylacetic acid serving as carbon and energy sources is overcome by cAMP. cAMP does not influence the basal rate of the enzyme synthesis (without the inducer). Derepression of synthesis of penicillinamidohydrolase by cAMP in a medium with glucose and inducer (phenylacetic acid) is associated with utilization of the inducer, due probably to derepression of other enzymes responsible for degradation of phenylacetic acid. Lactate can serve as a "catabolically neutral" source of carbon suitable for the maximum production of penicillinamidohydrolase. The gratuitous induction of the enzyme synthesis in a medium with lactate as the carbon and energy source and with phenylacetic acid is not influenced by cAMP; however, cAMP overcomes completely the absolute catabolite repression of the enzyme synthesis by glucose.

Regulation of the dicarboxylic acid part of the citric acid cycle in Bacillus subtilis

The regulation of alpha-ketogluterate dehydrogenase, succinate dehydrogenase, fumarase, malate dehydrogenase, and malic enzyme has been studied in Bacillus subitilis. The levels of these enzymes increase rapidly during late exponential phase in a complex medium and are maximal 1 to 2 h after the onset of sporulation. Regulation of enzyme synthesis has been studied in the wild type and different citric acid cycle mutants by adding various metabolites to the growth medium. Alpha-ketoglutarate dehydrogenase is induced by glutamate or alpha-ketoglutarate; succinate dehydrogenase is repressed by malate; and fumarase and malic enzyme are induced by fumarate and malate, respectively. The addition of glucose leads to repression of the citric acid cycle enzymes whereas the level of malic enzyme is unaffected. Studies on the control of enzyme activities in vitro have shown that alpha-ketoglutarate dehydrogenase and succinate dehydrogenase are inhibited by oxalacetate. Enzyme activities are also influenced by the energy level, expressed as the energy charge of the adenylate pool. Isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, and malic enzyme are inhibited at high energy charge values, whereas malate dehydrogenase is inhibited at low energy charge. A survey of the regulation of the citric acid cycle in B.subtilis, based on the present work and previously reported results, is presented and discussed.

Suppression of initiation-negative strains of Escherichia coli by integration of the sex factor F

Data are presented suggesting that the most critical factor determining whether an Hfr dnaAts strain can synthesize deoxyribonucleic acid and form colonies at temperatures that are nonpermissive for corresponding F- strains is neither the site of insertion of F nor the presence of additional mutations in the F particle or the chromosome; it is whether the particle is capable of autonomous replication at the temperature used. Consequently, suppression of the DnaA phenotype in Hfr strains occurs at 40 C but not, in most of them, at 42 C without the occurrence of additional mutations. The site of insertion of F may also be important since it is shown that in one Hfr dnaA strain partial suppression does occur at 42 C. In addition, it is shown that strains exhibiting suppression by integration of F at 40 C on minimal agar plates do not do so at this temperature on nutrient agar plates.

Catabolite repression and derepression of arylsulfatase synthesis in Klebsiella aerogenes

When a mutant (Mao(-)) of Klebsiella aerogenes lacking an enzyme for tyramine degradation (monoamine oxidase) was grown with d-xylose as a carbon source, arylsulfatase was repressed by inorganic sulfate and repression was relieved by tyramine. When the cells were grown on glucose, tyramine failed to derepress the arylsulfatase synthesis. When grown with methionine as the sole sulfur source, the enzyme was synthesized irrespective of the carbon source used. Addition of cyclic adenosine monophosphate overcame the catabolite repression of synthesis of the derepressed enzyme caused by tyramine. Uptake of tyramine was not affected by the carbon source. We isolated a mutant strain in which derepression of arylsulfatase synthesis by tyramine occurred even in the presence of glucose and inorganic sulfate. This strain also produced beta-galactosidase in the presence of an inducer and glucose. These results, and those on other mutant strains in which tyramine cannot derepress enzyme synthesis, strongly suggest that a protein factor regulated by catabolite repression is involved in the derepression of arylsulfatase synthesis by tyramine.

Effect of cyclic guanosine 3,5-monophosphate on the synthesis of enzymes sensitive to caatabolite repression in intact cells of Escherichia coli

Cyclic guanosine 3',5'-monophosphate inhibits the synthesis of beta-galactosidase and tryptophanase in cultures of Escherichia coli growing in minimal media with glucose or glycerol as the carbon source. Cyclic guanosine 3',5'-monophosphate acts at the transcriptional level in the lac operon, it exerts its action at the promoter site of the operon, and requires the presence of functional cyclic adenosine 3',5'-monophosphate receptor protein.