Regulation of lac mRNA synthesis in a soluble cell-free system

Overexpressed ribosomal proteins suppress defective chaperonins in Saccharomyces cerevisiae

The chaperonin Cct complex of the yeast Saccharomyces cerevisiae is composed of eight different subunits encoded by eight essential genes, CCT1-CCT8. This Cct complex is responsible for the folding of a number of proteins including actin and tubulin. We have isolated and characterized 22 multicopy suppressors of the temperature-sensitive allele, cct4-1, which encodes an altered protein with a G345D replacement that diminishes ATP hydrolysis. Fourteen of the suppressors encode ribosomal proteins, four have roles in ribosome biogenesis, two have phosphatase activities, one is involved in protein synthesis and one of the suppressors corresponded to Cct4p. Some of the suppressors also acted on certain cct1, cct2, cct3 and cct6 mutations. We suggest that certain overexpressed ribosomal and other proteins can act as weak chaperones, phenotypically alleviating the partial defects of mutationally altered Cct subunits.

19F n.m.r. studies of conformational changes accompanying cyclic AMP binding to 3-fluorophenylalanine-containing cyclic AMP receptor protein from Escherichia coli

A fluorine-containing analogue of the cyclic AMP (cAMP) receptor protein (CRP) from Escherichia coli was prepared by biosynthetic incorporation of 3-fluorophenylalanine (3-F-Phe). 19F n.m.r. studies on this protein have provided direct evidence for cAMP-induced conformational changes not only within the cAMP-binding domain but also within the hinge region connecting the cAMP-binding domain to the DNA-binding headpiece. At 313 K, the 19F n.m.r. spectrum of [3-F-Phe]CRP showed five signals corresponding to the five phenylalanine residues as expected for a symmetrical dimer. Proteolysis of [3-F-Phe]CRP with subtilisin produced a fragment (the alpha-fragment) containing the cAMP-binding domain. The alpha-fragment contains all the phenylalanines except for Phe-136, a residue located in the hinge region. By comparing the 19F spectra of [3-F-Phe]CRP and its alpha-fragment, the signal for Phe-136 was assigned. The chemical shifts of the corresponding signals in the two spectra are similar, indicating that the alpha-fragment retains the structure it has in the intact protein. The largest cAMP-induced shift was observed for the signal from Phe-136 providing direct evidence for a conformational change in the hinge region. However, whereas binding of a single cAMP molecule to a CRP dimer is known to be sufficient to activate the DNA binding, the n.m.r. data indicate that the hinge region does not have the same conformation in both subunits when only one cAMP molecule is bound.

19F NMR evidence for interactions between the c-AMP binding sites on the c-AMP receptor protein from E. coli

The 19F NMR spectra of 3-fluorotyrosine containing c-AMP receptor protein (CRP) from E. coli have been recorded in the presence of increasing amounts of c-AMP. One of the signals (from Tyr B) shifts upfield by 0.6 ppm in the presence of excess c-AMP and shows both slow and fast exchange behaviour during the titration. This is evidence for interactions between the two c-AMP binding sites on the CRP dimer leading to different dissociation rate constants (less than or equal to 75 s-1; greater than or equal to 350 s-1) for complexes containing one and two c-AMP molecules.

19F-n.m.r. studies of ligand binding to 5-fluorotryptophan- and 3-fluorotyrosine-containing cyclic AMP receptor protein from Escherichia coli

Two fluorine-containing analogues of the cyclic AMP receptor protein (CRP) from Escherichia coli were prepared by biosynthetic incorporation of 5-fluorotryptophan (5-F-Trp) and 3-fluorotyrosine (3-F-Tyr). The 19F-n.m.r. spectrum of the [5-F-Trp]CRP showed two signals corresponding to the two tryptophan residues, and that of the [3-F-Tyr]CRP showed six signals (two overlapping) corresponding to the six tyrosine residues: these results are as expected for a symmetrical dimer. A comparison of the 19F-n.m.r. spectra of the CRP analogues in the presence and in the absence of cyclic AMP reveals that the chemical shifts of both tryptophan residues and of two of the six tyrosine residues show differences. Since none of these residues is in direct contact with the bound nucleotide (although Trp-85 is fairly close), these shift changes must arise from induced conformational effects. The 19F-n.m.r. spectra of complexes with cyclic GMP showed chemical-shift perturbations different from those caused by cyclic AMP, indicating that different conformational changes are induced by the binding of cyclic GMP. The 19F-n.m.r. spectrum of the complex of [3-F-Tyr]CRP with tubercidin 3',5'-(cyclic)monophosphate (which can activate transcription) showed essentially the same chemical-shift changes as seen for the cyclic AMP complex, indicating that similar conformational changes have been induced by the nucleotide binding. [3-F-Tyr]CRP in the presence of an equimolar amount of the 20 bp self-complementary DNA oligomer 5'-AATGTGAGTTAACTCACATT-3' and excess cyclic AMP gave an 19F-n.m.r. spectrum that was almost identical with that for the [3-F-Tyr]CRP-cyclic AMP complex, indicating that the binding of DNA does not induce significant conformational changes involving the tyrosine residues. Proteolysis of [3-F-Tyr]CRP with chymotrypsin produced a 31 kDa fragment that is a dimer containing the cyclic AMP-binding domain. This fragment contains five of the six tyrosine residues, and its 19F-n.m.r. chemical shifts were essentially the same as those of the intact protein except for one missing signal (signal F): this signal could be assigned to Tyr-206 and shown to be unperturbed by the binding of cyclic nucleotide to the intact [3-F-Tyr]CRP. The similarity of the 19F-n.m.r. chemical shifts in the alpha-fragment and the intact CRP indicates that the alpha-fragment retains the same structure as found in the intact protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of the lac promoter and its variants. Synergistic effects of catabolite activator protein and supercoiling in vitro

Escherichia coli lac promoter variants are shown to be subject to large synergistic transcriptional activation by catabolite activator protein (CRP) and DNA supercoiling in vitro. Activation was studied for the lac wild-type promoter, a promoter with a variant spacing (lac delta l) and two promoters with variant -10 regions (lac ps, lac UV5). The variant promoters respond to the simultaneous presence of CRP and supercoiling by exhibiting large multiplicative activation at the low to moderate superhelicities that are most pertinent in vivo. Although all four promoters can be activated by CRP, those made stronger by changing downstream promoter elements are less CRP-activated even though each contains an identical CRP binding site. When each of the variant promoters is made stronger by introducing DNA supercoils, the apparent CRP activation initially remains constant but eventually declines at higher superhelicities. Thus, strengthening the lac promoter through either DNA sequence changes or the introduction of high-level DNA supercoiling can lead to diminished potential for activation by CRP. These results are interpreted in terms of a role for CRP in providing extra stabilizing contacts for RNA polymerase binding that are necessary only when other stabilizing features of promoter structure are lacking.

All three elements of the lac ps promoter mediate its transcriptional response to DNA supercoiling

The supercoiling response of four closely related promoters was examined in vitro. It was found that changes in all three elements of the lac ps promoter, i.e. the -10 sequence, the -35 sequence, and the spacer length, alter the transcriptional response to DNA supercoiling. Thus, the promoter as a whole, not just the melted region, mediates the supercoiling response. It is proposed that DNA supercoiling changes the structure of the promoter DNA to a form that can be recognized by RNA polymerase and then easily melted. All four promoter variants tested show the same qualitative response to the introduction of DNA supercoiling; that is, transcription is increased compared to relaxed DNA. However, for three of the four promoters, the rate peaked at intermediate levels of supercoiling and declined at higher superhelicities. Each mutation was found to alter both the extent of stimulation that can be achieved and the amount of superhelicity associated with maximal stimulation. The trend is that the stronger promoters are stimulated less, and this maximal stimulation occurs on templates containing fewer superhelical turns. At the level of supercoiling that may pertain in vivo, changes in superhelicity would result in considerable differential changes in the strengths of these promoters.

Entry of RNA polymerase at the lac promoter

The pathway of RNA polymerase entry at the lac promoter was studied by investigating the relationship between the promoter and a weak, overlapping polymerase interaction site (P2). If polymerase is made to enter the DNA by binding in vitro at this P2 site, cyclic AMP receptor protein (CRP) actively removes polymerase and redirects it to the promoter. A template competition experiment demonstrates that RNA polymerase initially bound at P2 does not slide the 22 base pairs along the DNA from this "entry" site to the promoter, but must locate the promoter by first leaving the template. We infer that CRP works by binding DNA in a way that both clears the promoter and modifies it to assume a form that is a better receptor for the binding of RNA polymerase from free solution.

Specific binding of the cAMP receptor protein of Escherichia coli to the lactose operon promoter

The nitrocellulose filter binding assay has been used to study effects of pH, temperature, ionic strength and magnesium ions on the specific binding of the cyclic adenosine 3',5'-monophosphate (cAMP) receptor protein (CAP) to the promoter of the lactose (lac) operon of Escherichia coli. The pH has a significant effect on binding with the greatest amount of specific binding appearing at pHs near 7 with a gradual decrease in binding as the pH is increased to 8. Specific binding was observed at temperatures of 22 degrees C and 37 degrees C but not at 4 degrees C. The specific binding was also found to be a function of the concentration of magnesium acetate and potassium chloride, being dependent on the specific cation present, the total ionic strength, and the concentration of the CAP protein. All binding decreases as the ionic strength, increases, but this decrease occurs at a lower ionic strength in magnesium acetate than in potassium chloride. In a double label experiment the filter assay demonstrates that the cAMP-CAP complex preferentially binds to the wild-type lac promoter in the presence of a lac promoter mutated at the CAP binding site. Based on these results and comparisons with other experiments reported in the literature, buffer conditions that approximate the physiological state of a cell appear to be best for studying the interaction between CAP and the lactose promoter in vitro.

Cyclic adenosine 3',5'-monophosphate-mediated hyperinduction of araBAD and lacZYA expression in a crp mutant of Escherichia coli K-12

A spontaneous lac+ revertant of an adenylate cyclase deletion strain of Escherichia coli K-12 was isolated and characterized. This revertant, designated strain KC20, exhibited a pleiotropic suppression of the adenylate cyclase defect, with the crp locus being the site of the suppressor mutation. Cyclic adenosine 3',5'-monophosphate at an exogenous concentration of 1 mM severely inhibited the growth of strain KC20 in minimal media. Lower concentrations of the cyclic nucleotide elicited less pronounced effects. Studies on araBAD and lacZYA expression showed that cyclic adenosine 3',5'-monophosphate elicited an initial dose-dependent hyperinduction of these systems. Hyperinduction of araBAD, in L-arabinose grown cultures of strain KC20, resulted in accumulation of inhibitory concentrations of methylglyoxal. Hyperinduction of lacZYA in lactose-grown cultures of strain KC20 did not result in any such methylglyoxal production.

Mechanism for transcriptional action of cyclic AMP in Escherichia coli: entry into DNA to disrupt DNA secondary structure

Binding analysis with purified bacterial receptor distinguishes two structural domains in cyclic AMP (cAMP). The first, the cyclic phosphate and furanose, constitutes a binding domain. This region is bound tightly to the receptor. The rest of cAMP is not bound; the adenine moiety of cAMP is exposed. Unlike binding, activity of cAMP requires the adenine moiety. To be active, cAMP must have in domain II the base adenine--specifically, its Watson--Crick atoms N-1 and N-6. Analysis of indoleacetic acid, a compound able to replace cAMP at the L-arabinose operon, indicates a similar distinction between binding and active domains. To be active, the indole must have substitution (carboxyl or amide) electronically comparable to the cAMP N-1 and N-6. On this basis, we propose a detailed mechanism for action of cAMP (or indoleacetic acid) in Escherichia coli. We propose that the exposed adenine of cAMP enters into the DNA. The adenine's N-1 and N-6 form hydrogen bonds to a thymine in DNA. This interaction destabilizes the DNA. It enhances transcription. Marked similarities indicate an identical mechanism for the steroid hormones in eukaryotes.

Regulation of toxinogenesis in Corynebacterium diphtheriae. I. Mutations in bacteriophage beta that alter the effects of iron on toxin production

Diphtherial toxin is produced in maximal yields by Corynebacterium diphtheriae (C7(beta tox+) only when iron is present in growth-limiting amounts. Toxin production is markedly decreased under high-iron conditions. We studied the role of the bacteriophage beta genome in this apparent regulation of toxin production by iron. Using a passive immune hemolysis assay to detect toxin antigen production in individual plaques, we identified rare phage mutants that were toxinogenic in high-iron medium. Lysogenic derivatives of C. diphtheriae C7 harboring such phage mutants were constructed. The lysogens were compared with wild-type strain C7(beta) for their ability to produce toxin in deferrated liquid medium containing varying amounts of added iron. Quantitative tests for extracellular toxin were performed by competitive-binding radioimmunoassays. We identified phenotypically distinct mutant strains that produced slightly, moderately, or greatly increased yields of toxin antigen under high-iron conditions. The toxin produced by the mutant lysogens was biologically active and immunochemically indistinguishable from wild-type toxin. Complementation experiments demonstrated that the phage mutation designated tox-201 had a cis-dominant effect on the expression of the toxin structural gene of phage beta. The characteristics of the tox-201 mutation suggest that it defines a regulatory locus of phage beta that is involved in control of toxinogenesis by iron in C. diphtheriae.

Hydrogenase genes

For a variety of reasons, including the potential industrial applications of hydrogenase, we are interested in the isolation and analysis of hydrogenase genes. In a program focusing on the hydrogen bacterium A. eutrophus H1 and E. coli, we have developed a preliminary concept of the interaction of hydrogenase in cellular metabolism, constructed mutants deficient in hydrogenase activity, and begun the isolation of hydrogenase genes utilizing the technology allowing the in vitro manipulation of DNA. We hope to pursue this project to its ultimate goal: the analysis of the molecular mechanisms involved in the control of expression of these genes and the development of the ability to manipulate the production of hydrogenase.

Mechanism of the rel defect in beta-galactosidase synthesis

Relaxed (relA) mutants of Escherichia coli are defective in beta-galactosidase synthesis during amino acid limitation. We show here that this defect comprises both a transcriptional component and a translational component.

In vivo role of the relA+ gene in regulation of the lac operon

Under conditions of amino acid limitation, beta-galactosidase was produced at a 70-fold higher rate in a relA+ strain than in an isogenic relA strain of Escherichia coli K-12. Under identical conditions with the relA+ and relA strains carrying various lac promoter mutations, rates of beta-galactosidase synthesis in relA+ (relative to relA) ranged from 26-fold higher (promoter mutant Pr 13) to only 5-fold higher (promoter mutant PrL8uv5). This promoter specificity was independent of strain background and the means of eliciting amino acid limitation. Addition of cyclic AMP to the growth medium altered the relA+/relA difference for beta-galactosidase synthesis from the wild-type lac promoter. The experiments suggest that the relA+/relA difference in lac expression arises primarily at the point of transcription initiation. The results are discussed in relation to recent in vitro data showing a promoter-specific guanosine 5'-diphosphate 3'-diphosphate stimulation of lac transcription (P. Primakoff and S. W. Artz, Proc. Natl. Acad. Sci. U.S.A. 76:1726-1730).

The effect of urea on catabolite sensitive operons in Escherichia coli K 12

Low concentrations of urea specifically inhibit the expression of catabolite sensitive genes (the lactose, galactose and maltose operons and the tryptophanase gene). This inhibition depends upon growth conditions, i.e. carbon source and temperature. The main effect of urea is exerted at the level of transcription initiation. However an additional inhibitory effect is observed on the decay and expression of the beta-galactosidase messenger. In a strain harboring the UV5 mutation in the lactose promoter, the effect at the level of transcription is relieved while the effect on the decay and the expression of the beta-galactosidase messenger remains the same. Just like the extreme physiological catabolite repression, the urea effect occurs even in a cya delta strain and is not antagonized by addition of adenosine 3'-5' cyclic monophosphate.

Alterations in two conserved regions of promoter sequence lead to altered rates of polymerase binding and levels of gene expression

Characterization of recombinant lac promoters highlights the importance of two regions of sequence conservation in promoters. The "Pribnow box" sequences are necessary for specific transcription in this system. This specificity is maintained when a mutated upstream sequence is introduced. However, changing the upstream DNA sequences influences both the rate of RNA polymerase binding in vitro and levels of expression in vivo.

The construction in vitro of derivatives of bacteriophage lambda carrying the amidase genes of Pseudomonas aeruginosa

The amidase genes of Pseudomonas aeruginosa were inserted into a lambda replacement vector following cleavage with the restriction endonuclease HindIII. The recombinant lambdaami was detected by enhanced growth of Escherichia coli around plaques of the recombinant phage on minimal medium containing acetamide as the nitrogen source. Low levels of amidase activity were detected in E. coli cultures infected with lambdaami and these were sufficient to allow growth with acetamide as nitrogen source. Lysis-defective derivatives of lambdaami were made by introducing Q-, S-, mutations. Cultures of E. coli infected with lambdaamiQ-S- synthesised amidase as the major protein. The amidase produced by these cultures was identical to that produced by PAC strains of P. aeruginosa in substrate specificty, thermal stability and immunological cross-reaction.

Glucocorticoid regulation of mouse mammary tumor virus gene expression

Glucocorticoid hormones act rapidly and specifically to stimulate the synthesis of mouse mammary tumor virus RNA in a variety of mouse mammary tumor cells and infected heterologous cells. The increase in viral RNA production appears to be mediated by receptor proteins and requires the presence of basal levels of viral RNA. Infection of heterologous cells with MMTV may alter host cell responses to glucocorticoids; in addition, production of unintegrated viral DNA in these cells has provided reagents required for studying the structure and function of the viral DNA itself. The advent of new techniques for genetic manipulation of eukaryotic cells and for isolation of large amounts of specific DNA sequences should now permit detailed analyses of steroid hormone action in this system.

Effect of guanosine 5'-diphosphate 3'-diphosphate and related nucleoside polyphosphates on induction of tryptophanase and beta-galactosidase in permeabilized cells of Escherichia coli

Exogenous addition of guanosine and adenosine 5'-(mono, di and tri) phosphate 3'-diphosphates (pppGpp, ppGpp, pGpp, pppApp, ppApp and pApp) stimulated the synthesis of tryptophanase and beta-galactosidase in permeabilized cells of Escherichia coli. From the results obtained with ppGpp and pppApp, this effect appeared to be at a transcriptional level and depended greatly on the growth condition; the largest effect was observed in cells under shiftdown or grown on poor enrgy source. ppGpp and pppApp, unlike cyclic AMP, did not act to overcome the inhibition of enzyme induction by glucose, but in combination with cyclic AMP caused a synergistic stimulation effect. In the shiftdown cells, ppGpp and pppApp gave 30% or more stimulation effect on tryptophanase induction while cyclic AMP did not stimulate induction. There was therefore a pronounced difference between cyclic AMP and ppGpp or pppApp in stimulatory function.

Effect of guanosine tetraphosphate on in vitro protein synthesis directed by E1 and E3 colicinogenic factors

The in vitro synthesis of colicin E3 was found to be stimulated by guanosine 5'-diphosphate 3'-diphosphate (ppGpp), while that of several other ColE3 plasmid-specific proteins was reduced in the presence of this nucleotide. The ColE1 plasmid-directed in vitro synthesis of colicin E1 was also found to be stimulated by ppGpp.

In vitro synthesis of cystathionine gamma-synthetase in Escherichia coli K-12

Synthesis of cystathionine gamma-synthetase directed by DNA from a lambdadmet transducing phage has been achieved in cell extracts from Escherichia coli K-12. Enzyme synthesis was stimulated two- to threefold by the addition of guanosine 3'-diphosphate 5'-diphosphate to the incubation mixtures. Kinetic studies showed a 1.5- to 2.0-min lag between initiation of transcription and completion of a translatable message. This lag is shorter than that observed for beta-galactosidase synthesis with DNA from a lac transducing phage known to initiate transcription at the lac promoter. This result, together with information on the structure of the transducing phage, shows that pL is not used for initiation of in vitro metB transcription. Attempts to demonstrate repression were not successful, and unexpectedly, extracts from metJ+ strains were found to be more effective at enzyme synthesis than those from their metJ derivatives.

In vitro synthesis of beta-galactosidase with ilv-lac fusion deoxyribonucleic acid as template

An in vitro protein-synthesizing system has been developed to study the mechanism of induction of ilvC gene in Escherichia coli strain K-12. Deoxyribonucleic acid (DNA) from a lambda phage carrying an ilvC-lac fusion was employed as a template for the in vitro synthesis of beta-galactosidase under the control of the ilvC promoter. The use of this template allowed an investigation of the components required for induction of the ilvC gene and the kinetics of the induction. The in vitro synthesis of beta-galactosidase under the control of the ilvC promoter was found to be DNA, acetohydroxy acid, and guanosine-3'-diphosphate-5'-diphosphate dependent, and sensitive to rifampin, actinomycin D, and chloramphenicol. Uncoupling experiments indicate that the inducer, acetohydroxybutyrate, acts at the transcriptional level. Investigation of a proposed noninducible ilvC regulatory mutant has shown normal induction in vitro. It was also observed that an intact ilvA gene is not required for the induction of the ilvC gene.

The effect of translation and transcription inhibitors on the synthesis of periplasmic phosphatases in E. coli

Previous studies by others have indicated that the synthesis of secreted enzymes is unusually sensitive to many translation inhibitors and resistant, for about 30 min, to rifampicin. We have studied the sensitivity of secreted (periplasmic) phosphatases to such inhibitors. Alkaline phosphatase synthesis is more sensitive than total protein synthesis to tetracyclin and spectinomycin, but not to sparsomycin, streptomycin, chloramphenicol, kasugamycin, blasticidin S or thiostrepton; it is slightly more resistant than total protein synthesis to the latter two antibiotics. Acid hexose-phosphatase was also preferentially sensitive to tetracyclin and spectinomycin and also to kasugamycin. beta-galactosidase was also included in the study, as an intracellular enzyme, and was found to be preferentially inhibited ("repressed"), sometimes transiently, by all eight translation inhibitors. This effect did not seem to be mediated through cyclic AMP or guanosine tetraphosphate; the "repression" was still evident in mutants with altered rho factor indicating that it may also not be related to artificial polarity. Synthesis of both periplasmic phosphatases was immediately inhibited by rifampicin. These results differ from those found in previous studies with other organisms and suggest a reappraisal of the usual interpretation of these phenomena.

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.

Effects of methylation of the beta-galactosidase genome upon in vitro synthesis of beta-galactosidase

A template DNA from phage lambdah80dlacp5 coding for the in vitro synthesis of beta-galactosidase was used to study the effect of DNA methylation by the alkylating agent, dimethyl sulfate (DMS). Increasing the levels of DMS up to 50 mM concentration in the incubation medium led to an increase of DNA methylation. When incubated for 10 min at 37 degrees C, 3-4% Of nucleotides were methylated. The increase was linear to about 0.6% nucleotide methylation level. A higher yield was obtained at 37 degrees C incubation temperature than at 20 degrees C. Methylation of lambdah80dlacp5 DNA alone without methylation of other factors in the incubation mixture caused inhibition of the synthesis of beta-galactosidase in vitro. Increasing levels of DNA methylation caused greater inhibition of the newly synthesized enzyme activity. Total protein and RNA synthesis was inhibited by the methylated DNA to a much lesser extent than the inhibition of enzyme activity. When the level of nucleotide methylation was 0.74%, only 2% of enzyme activity remained, but total protein and RNA synthetic activities were found to be 72% and 44%, respectively.

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.

Properties of adenyl cyclase and cyclic adenosine 3',5'-monophosphate receptor protein-deficient mutants of Escherichia coli

Several spontaneous cya and crp mutants of Escherichia coli have been selected as clones simultaneously resistant to phage lambda and nalidixic acid and characterized. Both cya and crp mutants have been found to grow as cocci with increased doubling times. They have increased resistance to some mutagens (methylmethanesulfonate, ultraviolet light, gamma rays), antibiotics (nalidixic acid, ampicillin), phages (lambda, T6), sublethal heat and hypotonic shock, and decreased resistance to neutral detergents (sodium dodecyl sulfate, sodium deoxycholate), a protein synthesis inhibitor (streptomycin), and a respiratory inhibitor (sodium azide). The nature of changes in cell parameters indicate fundamental alterations in the envelope structure of the cya and crp mutant cells. The new cya and crp mutants have been found to be multiply carbohydrate negative and nonmotile in conformity with similar previously isolated mutants. Studies of revertants and phi80 cya+ and phi80 cya transductants indicated that the pleiotropic phenotype is related to a single mutational event at the cya or the crp locus in the mutants.

Specificity of the stimulation of in vitro ribonucleic acid synthesis by guanosine 5'-diphosphate 3'-diphosphate

The in vitro synthesis of ribonucleic acid (RNA) by S-30 extracts of Escherichia coli K-12 is stimulated from two-to fourfold by 0.16 mM to 0.32 mM guanosine 5'-diphosphate 3'-diphosphate (ppGpp) when either gammacI857St68h80 deoxyribonucleic acid (gammah80 DNA), gammah80dilv DNA or gammah80dlac DNA are employed as templates. Hybridization analysis of the 3H-RNA product transcribed from gammah80dilv DNA in the presence of ppGpp indicates that both bacteriophage- and bacterial-specific transcription is stimulated to an equivalent degree. In the absence of cyclic 3'-5'-adenosine monophosphate (cyclic AMP), correct lac-specifci RNA synthesis from gammah80dlac DNA is not stimulated by 0.32 mM ppGpp although total RNA synthesis is increased nearly twofold. In the presence of 0.5 mM cyclic AMP, correct lacspecific RNA synthesis is stimulated preferentially by ppGpp. These data suggest that ppGpp is capable of stimulating in vitro transcription in both a general and selective manner.

Guanosine 5'-diphosphate 3'-diphosphate (ppGpp): positive effector for histidine operon transcription and general signal for amino-acid deficiency

Maximal expression of the histidine operon of Salmonella typhimurium in a coupled in vitro transcription-translation system is strongly dependent upon addition of guanosine 5'-diphosphate 3'-diphosphate (ppGpp). This requirement for ppGpp is exerted at the level of transcription through a mechanism distinct from the his-operon-specific regulatory mechanism. In vivo derepression of the his operon is markedly defective when histidine starvation is imposed on a relA mutant--unable to rapidly increase synthesis of ppGpp--growing in amino-acid-rich medium. Increased sensitivity of relA mutants to growth inhibition by a number of amino-acid analogs suggests that ppGpp is generally important in adjusting expression of amino-acid-producing systems. Analysis of these findings leads us to propose that ppGpp is a positive effector in a system that enables the cell to balance endogenous amino-acid production with environmental conditions of amino-acid availability, and to compensate efficiently for transient changes in these conditions. We propose a unifying theory of the role of ppGpp as the general signal molecule (alarmone) in a "super-control" which senses an amino-acid deficiency and redirects the cell's economy in response.

Deletion of the Escherichia coli crp gene

Spontaneous crp mutants Escherichia coli were selected from a strain that does not require 3',5'-cyclic adenosine monophosphate for CAP activity. Several deletions of the crp gene were characterized. The crp gene was not essential for growth of E. coli. crp mutations reduced the donor ability of Hfr strains.

Isolation of a catabolite repression mutant of yeast as a revertant of a strain that is maltose negative in the respiratory-deficient state

A character originating from Saccharomyces cerevisiae 1403-7A is described which interferes with maltose growth in the respiratory-deficient state. This character is inherited in an apparently non-Mendelian way, but at present no statement can be made concerning the localization of this character on a plasmid or the involvement of multiple genes. As a revertant of this character, a flaky mutant was isolated, showing a heavy flocculation during growth on liquid medium and resistance to catabolite repression for maltase, alpha-methyl-glucosidase, invertase, and succinate dehydrogenase. In wild-type cells, repression (caused by growth on 2% glucose) and derepression (caused by growth on 2% galactose) can be correlated with a lower and a higher level of cyclic 3',5'-adenosine monophosphate (cAMP), respectively. In cells of flaky mutant, growth on these carbon sources results in the same levels of cAMP as observed for the wild type. Consequently, in this mutant derepression in the presence of 2% glucose is not reflected in a higher level of cAMP.

Deoxyribonucleic acid-directed in vitro synthesis of ilv-specific messenger ribonucleic acid by extracts of Escherichia coli K-12

The synthesis of ilv-specific messenger ribonucleic acid (mRNA) by extracts of Escherichia coli K-12 has been demonstrated in a deoxyribonucleic acid (DNA)-dependent, coupled transcription-translation system. ilv-Specific mRNA was determined by hybridization either to double-stranded lambdacI857St68h80dilv DNA (lambdah80dilv DNA) immobilized on nitrocellulose filters or to its separate l and r strands in liquid. During conditions optimal for protein synthesis, slightly more than 6% of the total [(3)H]RNA synthesized by S-30 extracts of the threonine deaminase-negative strain CU5136 was ilv-specific. Of this RNA, nearly 30% was complementary to the l (correct) strand. Total ilv-specific mRNA synthesis in vitro was not affected by omission of valine or all 20 amino acids from the reaction mixture. Hybridization of ilv-specific mRNA made in vitro to the l strand of lambdah80dilv DNA was effectively reduced in the presence of unlabeled RNA extracted from an ilv derepressed strain but not from an ilv deletion strain. In a purified transcription system, employing commercial RNA polymerase, twofold more ilv-specific mRNA was synthesized than in the coupled system, but this increase was entirely due to greater transcription of the r (incorrect) strand. An S-30 extract prepared from a strain isogenic to strain CU5136 but derepressed for ilvA gene expression synthesized twofold more ilv-specific mRNA in the coupled system. The significance of these findings is discussed.

Regulation of maltodextrin phosphorylase synthesis in Escherichia coli by cyclic adenosine 3', 5'-monophosphate and glucose

Cyclic adenosine 3', 5'-monophosphate (AMP) stimulates maltodextrin phosphorylase synthesis in Escherichia coli cells induced with maltose. A maximal effect occurs at 2 to 3 mM cyclic AMP. The action of cyclic AMP is specific, inasmuch as adenosine triphosphate, 3'-AMP, 5'-AMP, adenosine, and dibutyryl cyclic AMP are inactive. Glucose, alpha-methyl glucoside, 2-deoxyglucose, and pyridoxal 5'-phosphate repress maltodextrin phosphorylase synthesis. This repression is reversed by cyclic AMP. The action of cyclic AMP appears to be at the transcriptional level, since cyclic AMP fails to stimulate phosphorylase production in induced cells in which messenger ribonucleic acid synthesis has been arrested by rifampin or by inducer removal. The two other enzymes involved in the metabolism of maltose, amylomaltase and maltose permease, are also induced in this strain of E. coli and affected by glucose and cyclic AMP in a manner similar to phosphorylase.

Alkaline phosphatase. Possible induction by cyclic AMP after cholera enterotoxin administration

The present studies were undertaken to determine the role, if any, of cyclic 3',5'-adenosine monophosphate (cyclic AMP) as a chemical inducer of rat liver alkaline phosphatase. Cholera enterotoxin, given intravenously to rats, led to a rapid rise in the activity of hepatic adenyl cyclase that was 7(1/2) times greater than control values in 6 h. Cyclic AMP levels were also significantly increased above control values while the activity of cyclic nucleotide phosphodiesterase was unchanged. Hepatic alkaline phosphatase activity was increased 5(1/2) times above control in 12 h, but its rise followed that of adenyl cyclase and cyclic AMP by several hours. Cycloheximide inhibited the rise of hepatic alkaline phosphatase but not that of adenyl cyclase. The administration of glucagon, a known stimulator of hepatic adenyl cyclase, and of dibutyryl cyclic AMP, led to similar striking increases in hepatic alkaline phosphatase activity. This alkaline phosphatase increase was blocked by the prior administration of cycloheximide. Bile duct ligation, a known stimulator of hepatic alkaline phosphatase activity, failed to produce any significant changes in adenyl cyclase or cyclic AMP. Concomitant treatment of rats with bile duct ligation and cholera enterotoxin or bile duct ligation and glucagon, had no additive effect on the increase in hepatic alkaline phosphatase activity, although the increase occurred earlier. These results suggest that: (a) cyclic AMP may act as an inducer of hepatic alkaline phosphatase: (b) the stimulation of hepatic alkaline phosphatase by cholera enterotoxin is mediated by cyclic AMP; (c) the rise in hepatic alkaline phosphatase following bile duct ligation is not mediated by cyclic AMP; (d) the same alkaline phosphatase in rat liver may be induced by two (or more) mechanisms, only one of which requires cyclic AMP.

Genetic characterization of mutations which affect catabolite-sensitive operons in Escherichia coli, including deletions of the gene for adenyl cyclase

Sixty-two spontaneous mutations have been characterized which reduce the level of expression of catabolite-sensitive operons. These mutations appear to affect either the crp (catabolite gene activator protein) or cya (adenyl cyclase) loci. No new loci have been discovered. Deletions of the cya gene do not remove an essential function. phi80 transducing phage for the cya gene have been used to do recombination and complementation studies on cya mutants.

Messenger ribonucleic acid synthesis and degradation in Escherichia coli during inhibition of translation

Various aspects of the coupling between the movement of ribosomes along messenger ribonucleic acids (mRNA) and the synthesis and degradation of mRNA have been investigated. Decreasing the rate of movement of ribosomes along an mRNA does not affect the rate of movement of some, and possibly most, of the RNA polymerases transcribing the gene coding for that mRNA. Inhibiting translation with antibiotics such as chloramphenicol, tetracycline, or fusidic acid protects extant mRNA from degradation, presumably by immobilizing ribosomes, whereas puromycin exposes mRNA to more rapid degradation than normal. The promoter distal (3') portion of mRNA, synthesized after ribosomes have been immobilized by chloramphenicol on the promoter proximal (5') portion of the mRNA, is subsequently degraded.