Block Copolymers Based on Ethylene and Methacrylates Using a Combination of Catalytic Chain Transfer Polymerisation (CCTP) and Radical Polymerisation

Two scalable polymerisation methods are used in combination for the synthesis of ethylene and methacrylate block copolymers. ω-Unsaturated methacrylic oligomers (MMA_n ) produced by catalytic chain transfer (co)polymerisation (CCTP) of methyl methacrylate (MMA) and methacrylic acid (MAA) are used as reagents in the radical polymerisation of ethylene (E) in dimethyl carbonate solvent under relatively mild conditions (80 bar, 70 °C). Kinetic measurements and analyses of the produced copolymers by size exclusion chromatography (SEC) and a combination of nuclear magnetic resonance (NMR) techniques indicate that MMA_n is involved in a degradative chain transfer process resulting in the formation of (MMA)_n -b-PE block copolymers. Molecular modelling performed by DFT supports the overall reactivity scheme and observed selectivities. The effect of MMA_n molar mass and composition is also studied. The block copolymers were characterised by differential scanning calorimetry (DSC) and their bulk behaviour studied by SAXS/WAXS analysis.

Photorefractive effect in LiNbO3-based integrated-optical circuits for continuous variable experiments

We investigate the impact of the photorefractive effect on lithium niobate integrated quantum photonic circuits dedicated to continuous variable on-chip experiments. The circuit main building blocks, i.e. cavities, directional couplers, and periodically poled nonlinear waveguides, are studied. This work demonstrates that photorefractivity, even when its effect is weaker than spatial mode hopping, might compromise the success of on-chip quantum photonics experiments. We describe in detail the characterization methods leading to the identification of this possible issue. We also study to which extent device heating represents a viable solution to counter this effect. We focus on photorefractive effect induced by light at 775 nm, in the context of the generation of non-classical light at 1550 nm telecom wavelength.

Elastic Response of Cementitious Gels to Polycation Addition

The high compressive strength of cementitious materials stems from the creation of a percolated network of calcium silicate hydrate (C-S-H) nanoparticles glued together by strong Ca²⁺-Ca²⁺ correlation forces. Although strong, the ion correlation force is short range and yields poor elastic properties (elastic limit and resilience). Here, the use of polycations to partially replace Ca²⁺ counterions and enhance the resilience of cementitious materials is reported. Adsorption isotherms, electrophoretic mobility, as well as small angle X-ray scattering and dynamic rheometry measurements, are performed on C-S-H gels, used as nonreactive models of cementitious systems, in the presence of different linear and branched polycations for various electrostatic coupling, that is, surface charge densities (pH) and Ca²⁺ concentrations. The critical strain of the C-S-H gels was found to be improved by up to 1 order of magnitude as a result of bridging forces. At high electrostatic coupling (real cement conditions), only branched polycations are found to improve the deformation at the elastic limit. The results were corroborated by Monte Carlo simulations.

Structure and Yielding of Colloidal Silica Gels Varying the Range of Interparticle Interactions

The relationship between interaction range, structure, fluid-gel transition, and viscoelastic properties of silica dispersions at intermediate volume fraction, Φv ≈ 0.1 and in alkaline conditions, pH = 9 was investigated. For this purpose, rheological, physicochemical, and structural (synchrotron-SAXS) analyses were combined. The range of interaction and the aggregation state of the dispersions were tuned by adding either divalent counterions (Ca(2+)) or polycounterions (PDDA). With increasing calcium chloride concentration, a progressive aggregation was observed which precludes a fluid-gel transition at above 75 mM of calcium chloride. In this case, the aggregation mechanism is driven by short-range ion-ion correlations. Upon addition of PDDA, a fluid-gel transition, at a much lower concentration, followed by a reentrant gel-fluid transition was observed. The gel formation with PDDA was induced by charge neutralization and longer range polymer bridging interactions. The refluidification at high PDDA concentrations was explained by the overcompensation of the charge of the silica particles and by the steric repulsions induced by the polycation chains. Rheological measurements on the so-obtained gels reveal broad yielding transition with two steps when the size of the silica particle clusters exceeds ≈0.5 μm.

Cold gelation of alginates induced by monovalent cations

A new reversible gelation pathway is described for alginates in aqueous media. From various samples differing by their mannuronic/guluronic content (M/G), both enthalpic and viscoelastic experiments demonstrate that alginates having a high M content are able to form thermoreversible assemblies in the presence of potassium salts. The aggregation behavior is driven by the low solubility of M-blocks at low temperature and high ionic strength. In semidilute solutions, responsive assemblies induce a strong increase of the viscosity below a critical temperature. A true physical gel is obtained in the entangled regime, although the length scale of specific interactions between M-blocks decreases with increasing density of entanglements. Cold setting takes place at low temperatures, below 0 °C for potassium concentrations lower than 0.2 mol/kg, but the aggregation process can be easily shifted to higher temperatures by increasing the salt concentration. The self-assembling process of alginates in solution of potassium salts is characterized by a sharp gelation exotherm and a broad melting endotherm with a large hysteresis of 20-30 °C between the transition temperatures. The viscoelastic properties of alginate gels in potassium salts closely depend on thermal treatment (rate of cooling, time, and temperature of storage), polymer and salt concentrations, and monomer composition as well. In the case of alginates with a high G content, a similar aggregation behavior is also evidenced at higher salt concentrations, but the extent of the self-assembling process remains too weak to develop a true gelation behavior in solution.

Synthesis and structural characterization of chitosan nanogels

Colloidal physical gels of pure chitosan were obtained via an ammonia-induced gelation in a reverse phase emulsion. The water weight fraction and the chitosan concentration in the water phase were optimized so as to yield nanogels with controlled particle size and size distribution. The spherical morphology of the nanogels was established by transmission electron microscopy with negative staining. Wide-angle X-ray scattering experiments showed that these gels were partially crystalline. The electrophoretic mobilities of the particles remained positive up to pH 7, above which the particles aggregated due to the charge neutralization. From the investigation on the colloidal stability of these nanogels in various conditions (pH, salt concentration, temperature), an electrosteric stabilization process of the particles was pointed out, related to the conformation of mobile chitosan chains at the gel-liquid interface. Therefore, the structure of the nanogels was deduced as being core-shell type, a gelified core of neutralized chitosan chains surrounded by partially protonated chains.

A novel synthesis of chitosan nanoparticles in reverse emulsion

Physical hydrogels of chitosan in the colloidal domain were obtained in the absence of both cross-linker and toxic organic solvent. The approach was based on a reverse emulsion of a chitosan solution in a Miglyol/Span 80 mixture, generally regarded as safe. Temperature and surfactant concentration were optimized, and the impact of the degree of acetylation (DA) and the molar mass of chitosan was investigated. When chitosan had a DA above 30%, only macroscopic gels were obtained, because of the predominance of attractive Van der Waals forces. The lower the molar mass of chitosan, the better the control over particle size and size distribution, probably as a result of either a reduction in the viscosity of the internal aqueous phase or an increase in the disentanglement of the polymer chain during the process. After extraction and redispersion of the colloid in an ammonium acetate buffer, the composition of the particles was around 80% of pure chitosan corresponding to a recovery of 60% of the original input. These new and safe colloids offer wide perspectives of development in further applications.

Nuclear receptors Nor1 and NGFI-B/Nur77 play similar, albeit distinct, roles in the hypothalamo-pituitary-adrenal axis

Studies in Nur77-deficient mice have shown that the basal regulation of hypothalamic and pituitary functions as well as the adrenocortical steroidogenesis in these animals is normal. This indicates that Nur77-related orphan receptors may substitute Nur77 functions in the hypothalamo-pituitary-adrenal axis by a compensatory mechanism. Nor1 is the most recently cloned member of the NGFI-B/Nur77 subfamily, and its properties are still largely unknown. We demonstrate here that Nor1 is expressed in the pituitary gland and adrenal cortex, and that ACTH and angiotensin II (AngII) treatment of adrenal fasciculata cells induces Nor1 expression. Time-course analysis with both hormones on steroidogenic capacity and the specific gene expression in adrenal cells strongly suggest that Nor1 is an intermediate in the long-term consequences of ACTH or AngII treatment. The Nor1 and NGFI-B/Nur77 amino acid sequence homology and the analysis of the trans-activation properties of Nor1 show that the overall structural and functional organization of the two proteins is similar. As observed with NGFI-B/Nur77, Nor1 activates the expression of genes encoding steroidogenic enzymes as P450c21, through its interaction with NGFI-B response element promoter sequences. In contrast, binding experiments of Nor1 with the palindromic NurRE sequence suggest that Nor1 is not an efficient substitute for the NGFI-B/Nur77 activation of the POMC gene expression in pituitary glands. All these results indicate that Nor1 and NGFI-B/Nur77 may play similar albeit distinct roles in the hypothalamo-pituitary-adrenal axis. Further experiments also show that the mechanisms responsible for the transcriptional regulation of Nor1 in adrenal cells appear to depend on the protein kinase A and protein kinase C cascades.

[Orbital complications of sinusitis in adults]

Orbital complications of sinusitis are rare in adults but delayed diagnosis is vision and life threatening. We report our experience in 6 patients to present clinical history, bacteriology and discuss the modality of treatment. There were 4 young men and 2 women, aged from 16 to 79 years old. Only one patient had an immunocompromised underlying condition (HIV infection). Four patients had preseptal abscesses and three post septal cellulitis or abscess (one patient had preseptal abscess and post septal abscess and hematoma). Two patients had a complete unilateral loss of light perception. Pathogens encountered were Streptococcus species: 4, strict anaerobes: 1, Pseudomonas aeruginosa: 1 (patient with AIDS). Patients recovered from infection with antibiotics in 6 and surgery in 5 but sequellar blindness occurred in 2 patients. Our experience emphasizes the necessity of antibiotic treatment in bacterial sinusitis and importance of early diagnosis and appropriate management of complications.

Cationic lipid DC-Chol induces an improved and balanced immunity able to overcome the unresponsiveness to the hepatitis B vaccine

Th1 and Th2 immune responses against antigens can be modulated by the use of adjuvants. Since antibody isotypes (IgG1 and IgG2a) and cytokines induced may reflect the Th differentiation taking place during the immune response, the humoral and cellular immune responses induced in mice against hepatitis B virus surface antigen (HBsAg) were examined when the antigen was either adsorbed to aluminum hydroxyde or administered with a new adjuvant the cationic lipid 3beta-[N-(N',N'-dimethylaminoethane)carbamoyl]cholesterol (DC-Chol). The use of DC-Chol increased antibody responses in responding BALB/c mice, induced more consistent IgG1 and IgG2a antibody responses in OF1 mice and overcame the nonresponse to HBsAg in B10.M mice. Furthermore, DC-Chol was able to induce cellular immune responses to HBsAg. The DC-Chol induced a balanced Th1/Th2 response, which enabled mice to overcome the inherited unresponsiveness to HBsAg encountered with aluminum-adjuvanted vaccine. Thus, the DC-Chol provides a signal to switch on both Th1 and Th2 responses, which may have important implications for vaccination against hepatitis B virus, as well as for enhancing weak immunogenicity of other recombinant purified antigens in a nonresponder population.

The polypyrimidine tract binding (PTB) protein interacts with single-stranded DNA in a sequence-specific manner

Polypyrimidine tract binding (PTB) protein is a cellular factor whose function is unknown. Various RNA or single-stranded DNA sequences have been shown to interact with PTB. In this paper, using laser UV crosslinking and electrophoretic mobility shift assays to probe DNA-protein interactions, we demonstrate that PTB binding at a single-stranded DNA target is highly sequence-specific. We provide data showing that PTB interacts with the top strand of the adenovirus major late promoter transcriptional initiator, a sequence rich in pyrimidine residues. We also demonstrate that PTB is organised into at least two different binding domains.

Unliganded thyroid hormone receptor alpha can target TATA-binding protein for transcriptional repression

Unliganded human thyroid hormone receptor alpha (hTR alpha) can repress transcription by inhibiting the formation of a functional preinitiation complex (PIC) on promoters bearing thyroid hormone receptor (TR)-binding elements. Here we demonstrate that hTR alpha directly contacts the TATA-binding protein (TBP) and that preincubation of hTR alpha with TBP completely alleviates TR-mediated repression in vitro. Using stepwise preassembled PICs, we show that hTR alpha targets either the TBP/TFIIA or the TBP/TFIIA/TFIIB steps of PIC assembly for repression. We also show that the repression domain of hTR alpha maps to the C-terminal ligand-binding region and that direct TR-TBP interactions can be inhibited by thyroid hormone. Together, these results suggest a model in which unliganded hTR alpha contacts promoter-bound TBP and interferes with later steps in the initiation of transcription.

The upstream stimulatory factor functionally interacts with the Alzheimer amyloid beta-protein precursor gene

The amyloid beta-protein precursor (APP) gives rise to the A beta peptide, which is deposited in the brains of patients with Alzheimer's disease and Down's syndrome. Overexpression of APP due to a third copy of the gene appears to correlate with very early onset of Alzheimer's disease neuropathology in the brains of Down's syndrome patients. Thus, the identification of the factors involved with transcriptional regulation of the APP gene could provide critical clues regarding the events leading to the formation of amyloid deposits. An overlapping AP-1/AP-4 site in the proximal promoter region (-39 to -49) of the human APP gene has previously been shown to increase transcription 4-fold. Here we identify the factor binding specifically to this element as the upstream stimulatory factor USF, unrelated to the c-fos/c-jun complex or the AP-4 factor. In vitro transcription and co-transfection studies show that USF activates transcription from the APP promoter and that the AP-1/AP-4 element participates in this activation. Modulation of APP expression via regulation of USF could potentially ameliorate the production of Alzheimer-augmented beta-amyloid.

[The Ko phenotype and fetal-maternal allo-immunization]

BACKGROUND

Very few people have no Kell antigens (phenotype Ko). They can develop antibodies to Kell antigens after transfusion, or the abortion of a Kell-positive fetus. This paper describes a case of immunization that may have been due to amniocentesis.

CASE REPORT

The eighth pregnancy of a woman required an amniocentesis on the 17th week for chromosomal study because she was 41 years old. She had 4 prior abortions. Her blood group was A Rh+. Her red cells were not tested for rare blood groups and antibodies to blood groups were not screened before and after amniocentesis. The newborn baby developed hemolytic anemia. On her 10th hour of life, her hemoglobin was 10.7 g% and her bilirubinemia 308 mumol/l. Her blood group was A Rh+. Indirect Coomb's test was positive in the mother, and the baby was given 3 exchange transfusions of O+, Ccee, K- blood. Further studies showed that the mother had phenotype Ko (A+, Ccce, K-, k-, Kpa-, Kpb-, Jsa-, Jsb-). The baby's phenotype was K-, k+, Kpa-, Kpb-, Jsa-, Jsb+. The mother was found to have a high titer of Ku antibodies.

CONCLUSION

This mother belongs to one of the 3 families known in the Reunion Island to have phenotype Ko. She had never been given transfusions, and prior abortions are unlikely to have played a role since no hemolysis was seen in further newborns. While amniocentesis is probably a major factor, its role cannot be determined because no pre-amniocentesis samples were analysed immunologically.

Effect of double-blind crossover selenium supplementation on biological indices of selenium status in cystic fibrosis patients

Twenty-seven cystic fibrosis patients received selenium supplementation (2.8 micrograms of sodium selenite per kilogram of body weight per day) or a placebo. This 5-month trial was conducted as a double-blind, placebo-controlled study. After an interval of 2 months, treatments of the two groups were interchanged (crossed over) for another 5-month period. A group of healthy subjects, living in the same area, was investigated simultaneously. No selenium deficiency was found either in plasma or in erythrocytes before the supplementation. This result was inconsistent with a previous study performed in 1988 in our laboratory. This change in selenium status can be explained by progress in the nutritional nursing care of children and by the addition of selenium to the diet. During the study, selenium concentrations in plasma decreased when patients received placebo treatment and increased during selenium intake. In one of the two groups a similar variation was found for glutathione peroxidase activities in plasma and erythrocytes, whereas erythrocyte selenium was normal and did not change in any group. Nowadays, in the Grenoble area, the selenium status of cystic fibrosis patients is close to normal. Nevertheless, this study indicates a fragile equilibrium, given that selenium concentrations cn be lowered by placebo or mildly increased by supplementation.

Effect of double-blind crossover selenium supplementation on biological indices of selenium status in cystic fibrosis patients

Twenty-seven cystic fibrosis patients received selenium supplementation (2.8 micrograms of sodium selenite per kilogram of body weight per day) or a placebo. This 5-month trial was conducted as a double-blind, placebo-controlled study. After an interval of 2 months, treatments of the two groups were interchanged (crossed over) for another 5-month period. A group of healthy subjects, living in the same area, was investigated simultaneously. No selenium deficiency was found either in plasma or in erythrocytes before the supplementation. This result was inconsistent with a previous study performed in 1988 in our laboratory. This change in selenium status can be explained by progress in the nutritional nursing care of children and by the addition of selenium to the diet. During the study, selenium concentrations in plasma decreased when patients received placebo treatment and increased during selenium intake. In one of the two groups a similar variation was found for glutathione peroxidase activities in plasma and erythrocytes, whereas erythrocyte selenium was normal and did not change in any group. Nowadays, in the Grenoble area, the selenium status of cystic fibrosis patients is close to normal. Nevertheless, this study indicates a fragile equilibrium, given that selenium concentrations cn be lowered by placebo or mildly increased by supplementation.

[Tracheal neurinoma simulating status asthmaticus in a child]

BACKGROUND

Neurilemmoma is a benign tumor that is rarely located in the trachea. A neurilemmoma in the intrathoracic part of the trachea can mimic severe status asthmaticus.

CASE REPORT

A 14 year-old girl was admitted because of persistent signs of status asthmaticus, despite bronchodilator therapy. She had no history of asthma. A worsening of the wheezing while she was in the intensive care unit led to intubation and respiratory support. X-rays showed pneumomediastinum. A dramatic improvement only followed replacement of the intratracheal tube. On the 5th day of the disease, tracheoscopy showed a sessile tumor obstructing two-thirds of the lumen, 3 cm above carena. Biopsy showed the tumor to be a neurilemmoma; it was excised. Scar tissue developed and was responsible for stenosis; it required laser therapy and an endotracheal prosthesis. Neither the girl nor her parents showed signs of neurofibromatosis.

CONCLUSIONS

An intrathoracic tracheal tumor can produce asthmatoid wheezing. A definitive diagnosis can be made only by tracheoscopy.

Cloning and sequencing of Pseudomonas genes determining sodium dodecyl sulfate biodegradation

The nucleotide sequences of two genes involved in sodium dodecyl sulfate (SDS) degradation, by Pseudomonas, have been determined. One of these, sdsA, codes for an alkyl sulfatase (58,957 Da) and has similarity (31.8% identity over a 201-amino acid stretch) to the N terminus of a predicted protein of unknown function from Mycobacterium tuberculosis. The other gene, sdsB, codes for a positive activator protein (33,600 Da) that has extensive similarity with the lysR family of helix-turn-helix DNA-binding activator proteins.

[Removal of two calcium hydroxide preparations: S.E.M. study]

Calcium hydroxide is one of the most often medication used for temporary treatment in endodontics. Different forms of preparation are available. The aim of this study is to evaluate in vitro the elimination of the pharmaceutical and the commercial forms of presentation. The aspect of the dentinal walls were analysed using SEM and X-ray microanalysis. The results show that Ca(OH)2 removal is difficult but there is no significant difference of elimination between the two forms.

Cloning and sequencing of PYBP, a pyrimidine-rich specific single strand DNA-binding protein

In the human transferrin gene promoter, PRI and DRI are positive cis-acting elements interacting respectively with two families of proteins, Tf-LF1 and Tf-LF2. In this paper, we report the purification from rat liver nuclei, of one of these factors, PYBP, as well as the cloning and the sequencing of its cDNA. PYBP is a DNA-binding protein, purified as a 58 kDa doublet which binds only to single strand pyrimidine-rich DNA present for example in PRI and DRI. The protein binds also to a similar polypyrimidine tract present in one of the two strands of a DNA regulatory element of the rat tyrosine aminotransferase gene enhancer. PYBP gene is transcribed ubiquitously as a roughly 2.8 kb RNA which is likely to be subject to an alternative splicing. PYBP is highly homologous to a mouse nuclear protein, as well as to PTB, its human version, which interacts specifically with the pyrimidine tracts of introns. Primary structure information and predicted secondary structure elements of the protein indicate that PYBP contains four sequence repeats. Each of these repeats appears to exhibit the typical RNA recognition motif found in several proteins interacting with RNA or single strand DNA. Finally several hypotheses concerning the biological function of PYBP are presented.

Bacteriophage T7 RNA polymerase-controlled specific gene expression in Pseudomonas

The rifampicin (Rif)-resistant RNA polymerase of phage T7 has proved invaluable for the exclusive over-expression, in Escherichia coli, of genes cloned downstream from the T7 phi 10 promoter [Tabor and Richardson, Proc. Natl. Acad. Sci. USA 82 (1985) 1074-1078]. Here, we demonstrate that the system can be extended to Gram-negative bacteria other than E. coli, by the use of compatible wide host range plasmids. As an example, the Rif-resistant in vivo synthesis and specific radiolabelling of E. coli galactokinase in Pseudomonas ATCC19151, is demonstrated. The incidental observation that 30 min after treatment with Rif, two polypeptides continue to be synthesized in plasmid-free Pseudomonas ATCC19151, indicates that these proteins are produced by very stable mRNA species.

Interaction of DNA-binding proteins with the tissue-specific human apolipoprotein-AII enhancer

The identification of the binding sites for liver nuclear proteins present in the enhancer that control the cell specific transcription of the human apolipoprotein AII gene is reported. Five adjacent binding sites (motifs I to V) were identified. The motifs III, IV and V can be occupied differently by liver or HeLa nuclear proteins. Two hypersensitive zones (between motifs II-III and IV-V) are present only when liver nuclear extracts were tested. A first characterization of the factors reveal that motif IV interacts with the hepatic transcription factors Tf-LF1 (29) and LF-A1 (28, 30). A CCAAT binding protein, different from CTF/NF1, appears to bind to the motif II. The different binding sites share specific DNA sequences principally with 5' regulatory regions of other apolipoprotein genes.

Different liver nuclear proteins binds to similar DNA sequences in the 5' flanking regions of three hepatic genes

The proximal promoter region of the human transferrin gene contains an hepatocyte-specific cis-element (PRI, nucleotides -76 to -51) whose DNA sequence is homologous to a sequence (nucleotides -89 to -68) present in the transcriptionally essential 5' region of the human antithrombin III gene and to another hepatocyte-specific sequence (A domain) of the human alpha 1-antitrypsin gene promoter. The results reported here lead to the conclusion that the liver trans-acting factor Tf-LF1, binding to the transferrin PRI cis-element interacts with the homologous antithrombin III region, but is different from the transcription factor LF-A1 interacting with the A domain of the alpha 1-antitrypsin promoter. The distal region DRI (nucleotides -480 to -454) of the human transferrin gene promoter presents in its core the same 10 nucleotide-long sequence as the PRI cis-element. We have previously shown that the liver protein Tf-LF2, binding to the DRI element is different from the Tf-LF1 trans-acting factor. In this paper we also show that Tf-LF2 is different from the transcription factor LF-A1 interacting with the alpha 1-antitrypsin promoter. The results allow us to conclude that at least three distinct liver nuclear proteins bind to different subsets of 5' DNA regions containing similar sequences. These sequences are present in genes expressed essentially in liver.

Cloning and sequencing of Pseudomonas genes encoding vanillate demethylase

A 2,598-base-pair (bp) SalI-HincII DNA fragment has been cloned which codes for vanillate demethylase, the enzyme responsible for the demethylation of vanillate (3-methoxy-4-hydroxybenzoate) to protocatechuate (3,4-dihydroxybenzoate). Complementation and insertional inactivation experiments have shown that this fragment carries two genes (vanA and vanB) which are predominantly cotranscribed from a promoter upstream of vanA. Nucleotide sequencing of the SalI-HincII fragment confirmed the genetic data: two open reading frames of 987 and 942 bp were present in the transcribed orientation. These had a very high G + C content in the third base of each codon, which is characteristic of Pseudomonas chromosomal genes. Expression of the genes in Escherichia coli with the T7 RNA polymerase-promoter system gave rise to two polypeptides of 36 and 33 kilodaltons which could be identified by deletion analysis as the products of vanA and vanB, respectively. A search of the protein sequence data bank indicated that the vanB gene product was related to the ferredoxin family.

Interactions of DNA-binding proteins with the 5' region of the human transferrin gene

We have established by transient expression experiments that the 620 base pairs upstream of the cap site of the human transferrin gene contain the information necessary for efficient expression of the gene in hepatoma cells HepG2 or Hep3B but not in HeLa cells. DNase I footprint analysis reveals that at least five distinct factors present in human or rat liver nuclear extracts interact with different sites of this region. One of these factors, binding to nucleotides -193 to -162, is closely related to or identical with the eukaryotic factor CCAAT-binding transcription factor/nuclear factor I; another one, binding to nucleotides -103 to -83 seems to be related to the CCAAT-binding protein. The binding sites of two other factors, not recognized by HeLa nuclear proteins, each contain an identical 10-nucleotide-long sequence (5' TCTTTGACCT 3') in reverse orientation, separated by 400 base pairs. Results of gel retardation assays, cross-competition experiments, and heat inactivation strongly suggest that the proteins binding to these sites are different. One of these sequences and the binding site of the CCAAT-binding protein related factor are located in the region between nucleotides -119 and -45. We have shown by transient expression experiments with 3' deleted vectors that this region is functionally essential for human transferrin gene expression.

Vectors with restriction site banks. V. pJRD215, a wide-host-range cosmid vector with multiple cloning sites

The construction of a new wide-host-range, restriction-site bank, cosmid-cloning vehicle (pJRD215) is described. The wide-host-range properties and the ability to be transferred by conjugation, extend genetic engineering to those Gram-negative species that cannot be transformed. The vector permits the cloning of genes from Gram-negative bacteria using a complementation screening procedure in a mutant host. This procedure is simplified by the possibility of construction of a cosmid gene bank so that only a few hundred clones need to be screened. Subsequent subcloning of the gene of interest is facilitated by the presence of at least 23 unique cloning sites.

A 'phase-shift' fusion system for the regulation of foreign gene expression by lambda repressor in gram-negative bacteria

A 'phase-shift' translation fusion vector was constructed in which mutually compatible restriction sites BamHI, BclI and BglII are positioned in such a manner that the cut point is in a different reading frame, immediately following the ATG start codon and ribosome-binding site of the lambda cro gene. The lambda cro gene is expressed from promoter pR and controlled by a thermosensitive (cI857) lambda repressor. The usefulness of the expression vector was demonstrated using a galK gene lacking the ATG start codon and fusing this to the pR promoter and ATG start codon of the lambda cro gene, resulting in cI857-regulated expression of galactokinase. The vector is of general use for foreign gene expression in Escherichia coli when the target gene has a compatible cohesive end (5'-GATC-3') at the N terminus (provided, for example, by a BamHI linker). The lambda cI857-pR-cro-galK cassette was cloned into pJRD215, a wide-host-range plasmid and transferred by conjugation to a variety of Gram-negative bacteria. In all cases, thermosensitive regulation of galactokinase could be demonstrated, though the levels of induction varied considerably. These results show that the powerful lambda pR promoter and the efficient lambda repressor can be used to regulate expression of foreign genes in Gram-negative organisms other than E. coli.

Localisation and characterization of a new rho-dependent transcription terminator from bacteriophage T5

Relatively few rho-dependent terminators have been described in the literature. This manuscript describes another such terminator, isolated from phage T5. Functional analysis, involving the generation of deletion subclones, has permitted the localization of the terminator on a 413 bp fragment. Attempts to further reduce the size of this fragment resulted in loss of terminator activity. DNA sequence analysis of the terminator region supports the model whereby a rho-dependent terminator is composed of a long region of non-translated unstructured DNA, which permits rho binding, followed by RNA polymerase pausing sites where termination (in the presence of rho) may occur. The results agree with the currently held hypothesis that, despite the many similarities found between various rho dependent termination sequences, no consensus can be defined for either the rho binding or the rho termination sites (1,2).