Antiviral Potential of Specially Selected Bulgarian Propolis Extracts: In Vitro Activity against Structurally Different Viruses

Propolis is a natural mixture of resins, wax, and pollen from plant buds and flowers, enriched with enzymes and bee saliva. It also contains various essential oils, vitamins, mineral salts, trace elements, hormones, and ferments. It has been found that propolis possesses antimicrobial, antiviral, and anti-inflammatory properties. We have studied the antiviral activity of six extracts of Bulgarian propolis collected from six districts of Bulgaria. The study was conducted against structurally different viruses: human coronavirus strain OC-43 (HCoV OC-43) and human respiratory syncytial virus type 2 (HRSV-2) (enveloped RNA viruses), human herpes simplex virus type 1 (HSV-1) (enveloped DNA virus), human rhinovirus type 14 (HRV-14) (non-enveloped RNA virus) and human adenovirus type 5 (HadV-5) (non-enveloped DNA virus). The influence of the extracts on the internal replicative cycle of viruses was determined using the cytopathic effect (CPE) inhibition test. The virucidal activity, its impact on the stage of viral adsorption to the host cell, and its protective effect on healthy cells were evaluated using the final dilution method, making them the focal points of interest. The change in viral infectivity under the action of propolis extracts was compared with untreated controls, and Δlgs were determined. Most propolis samples administered during the viral replicative cycle demonstrated the strongest activity against HCoV OC-43 replication. The influence of propolis extracts on the viability of extracellular virions was expressed to a different degree in the various viruses studied, and the effect was significantly stronger in those with an envelope. Almost all extracts significantly inhibited the adsorption step of the herpes virus and, to a less extent, of the coronavirus to the host cell, and some of them applied before viral infection demonstrated a protective effect on healthy cells. Our results enlarge the knowledge about the action of propolis and could open new perspectives for its application in viral infection treatment.

[The value of bone mineral density assessment by dual-energy x-ray absorptiometry for prediction of cardiovascular mortality in patients treated with hemodialysis]

AIM

Determine whether bone mineral density (BMD) assessed by dual-energy x-ray absorptiometry can be used as predictor of increased risk of death in hemodialysis patients.

MATERIALS AND METHODS

A prospective study was performed of 516 patients with chronic kidney disease treated with hemodialysis (men 265, women 251, mean age 44.811.4 years) who were observed for 5.73.2 years. Before inclusion in the study, in all patients was analyzed bone mineral density using dual-energy X-ray absorptiometry in three standard departments: lumbar vertebrae, proximal femur and distal forearm. The probability analysis of the outcome was carried out using the KaplanMeier method and Cox.

RESULTS

During follow-up period 111 (21.5%) patients died, 50.5% from cardiovascular events. Survival analysis by KaplanMeier method allowed to prove the increased risk of death from cardiovascular pathology in hemodailysis patients with low bone mineral density of all evaluated areas. Step-by-step multivariate Cox regression analysis showed that the T score of the femur, showing the difference of BMD of the patient with normal value of BMD for young adult, had the greatest prognostic significance.

CONCLUSION

Reduced bone mineral density in patients receiving hemodialysis is associated with an increased risk of death from cardiovascular disease. Dual energy x-ray absorptiometry can be used for assessment of this risk.

Probing the uniformity of hydrogen intercalation in quasi-free-standing epitaxial graphene on SiC by micro-Raman mapping and conductive atomic force microscopy

In this paper, micro-Raman mapping and conductive atomic force microscopy (C-AFM) were jointly applied to investigate the structural and electrical homogeneity of quasi-free-standing monolayer graphene (QFMLG), obtained by high temperature decomposition of 4H-SiC(0001) followed by hydrogen intercalation at 900 °C. Strain and doping maps, obtained by Raman data, showed the presence of sub-micron patches with reduced hole density correlated to regions with higher compressive strain, probably associated with a locally reduced hydrogen intercalation. Nanoscale resolution electrical maps by C-AFM also revealed the presence of patches with enhanced current injection through the QFMLG/SiC interface, indicating a locally reduced Schottky barrier height (Φ_B). The Φ_B values evaluated from local I-V curves by the thermionic emission model were in good agreement with the values calculated for the QFMLG/SiC interface using the Schottky-Mott rule and the graphene holes density from Raman maps. The demonstrated approach revealed a useful and non-invasive method to probe the structural and electrical homogeneity of QFMLG for future nano-electronics applications.

[Structural changes of eye chorioretinal complex after total cerebral ischemia and their correction]

Structural changes of eye chorioretinal complex were investigated in 40 adult male outbred albino rats after total transient cerebral ischemia using electron microscopy and morphometric analysis. Furthermore, the influence of a new sterically hindered phenolic antioxidant dibornol on these processes was estimated. Our studies demonstrated that total transient cerebral ischemia in rats resulted in the capillary thrombosis of the choriocapillary lamina of the uvea, structural disturbances of the blood-retinal barrier, degeneration of the retinal neurons and radial glia. Course administration of dibornol was shown to improve the microcirculation and to protect the retinal neuronal structures, pigment epithelium, and radial glia.

Thermal impurity reactions and structural changes in slightly carbonated hydroxyapatite

Lattice and surface impurity reactions and structural changes induced by them in slightly carbonated hydroxyapatite (SCHA) treated at 25-1100 degrees C were comprehensively studied. The SCHA was processed by a conventional wet synthesis at a high possible temperature(96 degrees C) using ammonium containing parent reagents. IR-spectroscopy, XRD, TG-DTA technique and mass spectrometric thermal analysis (MSTA) were employed for characterization of the samples. NH4+ with H3O+ in cationic-and CO3(2-) (A- and B-positions) with HPO4(2-) in anionic sites, and H2O, CO3(2-)(HCO3(-)) NO3(-), NxHy on the surface of particles were found and considered as impurity groups. Complicated changes in lattice constants of theSCHA stepwise annealed in air (for 2 h) were revealed; the changes were associated with reactions of the impurity groups. Filling the hexed sites with hydroxyl ions above 500 degrees C was shown to happen partly due to lattice reactions but was mainly owing to hydrolysis of the SCHA by water molecules in air. Decomposition of CO3(2-) groups proceeded through both thermal destruction and reactions with some of the impurity ions. The decarbonation in A-sites occurred at much lower temperatures (450-600 degrees C) than in B-sites (700-950 degrees C) and was first revealed to happen in two stages: due to an impurity reaction around 500 degrees C, and then through thermal destruction at 570 degrees C. A redistribution of CO3(2-) ions, decreasing in amount on the whole, was observed upon annealing above 500 degrees C. To avoid possible erroneous conclusions from TG-data, a sensitive method was shown to be required for monitoring gaseous decomposition products (such as the MSTA in this study), in case several impurity groups were present in a SCHA.

Investigation of the morphology of cell clones, derived from the mammalian EBTr cell line and their susceptibility to vaccine avian poxvirus strains FK and Dessau

The ability for replication of vaccine avian pox viral strains FK and Dessau in cell clones, derived from the EBTr cell line, derived from embryonic bovine trachea, was studied. The derived seven cell clones showed different morphological characteristics and diverse sensitivity to both vaccine avian pox viral strains. Hence, the EBTr-derived cell clones could be used for cultivation, as well as for differentiation of vaccine avian pox viral strains. In addition, studies have been undertaken to elucidate the possible use of cultivated strains in these heterologous cell culture system's vaccine avian pox viral strains for biotechnology, as well as for solving problems, related to infection of people with avian viruses.

Epsilon as an initiator of translation of CAT mRNA in Escherichia coli

Epsilon sequence (UUAACUUUA) has originally been found in the bacteriophage T7 gene 10 leader region. It enhances translation in Escherichia coli via base pairing with nucleotides 458-466 located in the helical domain #17 of 16S rRNA. We have recently reported that when the complementarity to 16S rRNA is extended, the epsilon is converted from an enhancer to an independent initiator of translation. Here we report the effect of two other structural parameters, positioning in mRNA and the degree of complementarity to 16S rRNA on the translation initiation activity of epsilon in E. coli cells. Our results show that epsilon displays maximal activity as a translational initiator at its natural 9-nucleotide-long complementarity to 16S rRNA and at a 16-nucleotide-long distance to the initiation codon. Under these conditions its efficiency is comparable with that of the consensus Shine-Dalgarno sequence.

A polylinker-derived sequence, PL, highly increased translation efficiency in Escherichia coli

Pokeweed (Phytolacca americana) antiviral protein (PAP) is a highly specific ribosome-inactivating glycosidase. The PAP gene was isolated and cloned in an expression vector containing a polylinker-derived sequence (PL) but devoid of a Shine-Dalgarno (SD) sequence. Surprisingly, E. coli cells transformed with this vector produced over twice the amount of PAP than that with the consensus SD sequence. Computer analysis of the 5' terminal region of PAP mRNA revealed a nucleotide sequence (ACCUACUCGAGUUAG) which was complementary to two domains in 16S rRNA. The heptanucleotide ACCUACU (box I) is complementary to nucleotides 1434-1440 and the GAGUUAG (box II) to nucleotides 507-513 in 16S rRNA of E. coli. To examine the role of this sequence in the translation of PAP mRNA, single or both boxes were mutated and the protein yield was measured. Mutation of box I and of box II resulted in a 2.7 and 5.3 fold decrease in protein yield respectively, indicating that the PAP gene expression was dependent on the presence of both boxes. To investigate whether PL also increases expression of other genes, human calcitonin monomeric and tetrameric genes were used as reporters. It was found that the expression level was doubled compared to that by SD. These results demonstrate that the PL is an efficient translational initiator and may be used for high level expression of certain genes in E. coli. The possible mechanisms for the high level expression are discussed.

Enhancing activity of epsilon in Escherichia coli and Agrobacterium tumefaciens cells

Epsilon (epsilon) sequence is a bacterial enhancer of translation found in the bacteriophage T7 gene 10. It is believed that its enhancing effect of epsilon is due to a base-pairing with the nucleotides 458-467 from the helical domain 17 of Escherichia coli 16S rRNA. To prove this we have taken advantage of the difference of this domain in Agrobacterium tumefaciens and E. coli. To evaluate the significance of nucleotide complementarity for the enhancing activity of epsilon, a series of nucleotide sequences matching either E. coli or A. tumefaciens domain 17 are cloned in a binary expression vector in front of the chloramphenicol acetyltransferase (CAT) gene. The CAT assay shows that: (i) the epsilon in combination with an SD consensus sequence increases the yield of CAT in both microorganisms over that obtained with the SD alone; (ii) the epsilon sequence complementary to the A. tumefaciens domain 17 leads to a 2.71-fold increase in the yield of CAT in homologous cells but not in E. coli cells; (iii) the yield of CAT correlates with the free energy of base-pairing with the helical domain 17 in both microorganisms.

Preparation and properties of inhomogeneous hydroxyapatite ceramics

Inhomogeneous ceramics of hydroxyapatite (HA) were prepared by sintering briquettes in which an inhomogeneous distribution of density was made by pressing HA powder into a die with rough walls. The resulting sample of such a ceramic is a hard thin shell with a loose core, and it is characterized by an inhomogeneous macro- and microstructure. It is a sintered conglomerate from HA grains containing grain boundary macropores in contact with the surface and micropores located inside the grains, part of which are also associated with the free surface. The highest value of microhardness is fixed on the surface of the sample. The radial distribution of microhardness in the (cylindrical) sample has an axisymmetric, nonmonotonic character and, on the whole, shows the decrease of microhardness (the increase of porosity) from the surface to the center. The highest values of microhardness, crushing strength, and fracture strength are close to those known for ceramics of moderate strength.

Non-enzymatic RNA hydrolysis promoted by the combined catalytic activity of buffers and magnesium ions

Although Mg2+ is an important cofactor for the specific degradation of RNA by ribozymes, it is not considered as a typical chemical nuclease. In this study we show that in combination with common buffers such as tris(hydroxymethyl)aminomethane and sodium borate, Mg2+ is a powerful catalyst for the degradation of RNA. pH and temperature are found to be the principal factors for the efficient degradation of RNA. Whereas in Tris-HCl/Mg2+ the efficient cleavage starts at pH values higher than 7.5 and temperatures higher than 37 degrees C, in sodium borate RNA degradation begins at pH 7.0 and at 37 degrees C. RNA hydrolysis promoted under the combined catalytic activity of buffer/Mg2+ results in partially degraded RNA and negligible amounts of acid-soluble material. Reaction is insensitive to the concentration of monovalent cations but is completely prevented by chelating agents (EDTA and citrate) at concentrations exceeding that of Mg2+. Borate-magnesium reaction is inhibited also by some polyvalent alcohols (glycerol) and sugars.

Possibilities for strengthening hydroxyapatite ceramics

Some physics during heating and sintering of powder pressings of hydroxyapatite (HA) under conventional (usual) conditions have been studied. It is revealed that heating and firing of the pressings of a middle-dispersity powder are accompanied by release of gases. The gas release hinders and can stop the shrinkage (sintering). The microhardness is low and has a complicated distribution on the surface and in the volume of ceramics. A slight degassing (drying) of the pressing before sintering heightens the density and improves the microhardness characteristics of the ceramics. The shrinkage stop effect is eliminated in pressings of a fine powder. On the basis of the results, a technique and some methods for quality improvement of ceramics were proposed and approbated. They consisted of the manufacture of samples of a mixture of two powders with different dispersity, use of a press technique with two male dies, thermal treatment of pressing before sintering, and the choice of moderate sintering conditions. The resulting ceramics had a density close to the theoretical, almost homogeneous microhardness distribution in the sample and much higher values of microhardness and compressive strength.

Efficiency of a novel non-Shine-Dalgarno and a Shine-Dalgarno consensus sequence to initiate translation in Escherichia coli of genes with different downstream box composition

The efficiency of a novel non-Shine-Dalgarno translational initiator (ACCUACUCGAGUUAG, denoted PL) to promote translation in Escherichia coli was compared with that of the Shine-Dalgarno (SD) consensus sequence (AAGGAGGU) using four reporter genes. The obtained results showed that the genes of pokeweed antiviral protein (PAP I) and human calcitonin (CT) were poorly expressed under the conventional SD and were better expressed under the PL sequence. On the contrary, the genes of human interferon gamma (hIFN gamma) and chloramphenicol acetyltransferase (CAT) were highly expressed under SD and poorly expressed under the PL sequence. Computer search revealed a great diversity between the four reporter genes in respect to their complementarity to E. coli 16S rRNA. PAP I and CT genes were rich in nucleotides matching 16S rRNA (called downstream boxes) whereas the complementary domains in the other two (hIFN-gamma and CAT) genes were much shorter. The different behavior of the four reporter genes when placed under the translational control of SD and PL sequences was explained by the different binding energy of their mRNAs to the 30S ribosomal subunit.

Effect of N-terminal deletions on the activity of pokeweed antiviral protein expressed in E. coli

Pokeweed antiviral protein (PAP) from Phytolacca americana is a highly specific N-glycosidase removing adenine residues (A4324 in 28S rRNA and A2660 in 23S rRNA) from intact ribosomes of both eukaryotes and prokaryotes. Due to the ribosome impairing activity the gene coding for mature PAP has not been expressed so far in bacteria whereas the full-length gene (coding for the mature 262 amino acids plus two signal peptides of 22 and 29 amino acids at both N- and C-termini, respectively) has been expressed in Escherichia coli. In order to determine: 1) the size of the N-terminal region of PAP which is required for toxicity to E. coli; and 2) the location of the putative enzymatic active site of PAP, 5'-terminal progressive deletion of the PAP full-length gene was carried out and the truncated forms of the gene were cloned in a vector containing a strong constitutive promoter and a consensus Shine-Dalgarno ribosome binding site. The ribosome inactivation or toxicity of the PAP is used as a phenotype characterized by the absence of E. coli colonies, while the mutation of PAP open reading frames in the small number of survived clones is used as an indicator of the toxicity to E. coli cells. Results showed that the native full-length PAP gene was highly expressed and was not toxic to E. coli cells although in vitro ribosome inactivating activity assay indicated it was active. However, all of the N-terminal truncated forms (removal of seven to 107 codons) of the PAP gene were toxic to E. coli cells and were mutated into either out of frame, early termination codon or inactive form of PAP (i.e., clone PAP delta107). Deletion of more than 123 codons restored the correct gene sequence but resulted in the loss of the antiviral and ribosome inactivating activities and by the formation of a large number of clones. These results suggest that full-length PAP (with N- and C-terminal extensions) might be an inactive form of the enzyme in vivo presumably by inclusion body formation or other unknown mechanisms and is not toxic to E. coli cells. However, it is activated by at least seven codon deletions at the N-terminus. Deletions from seven through to 107 amino acids were lethal to the cells and only mutated forms (inactive) of the gene were obtained. But deletion of more than 123 amino acids resulted in the loss of enzymatic activity and made it possible to express the correct PAP gene in E. coli. Because deletion of Tyr94 and Val95, which are involved in the binding of the target adenine base, did not abolish the activity of PAP, it is concluded that the location previously proposed for PAP enzymatic active site should be reassessed.

The low expression level of pokeweed antiviral protein (PAP) gene in Escherichia coli by the inducible lac promoter is due to inefficient transcription and translation and not to the toxicity of the PAP

Pokeweed (Phytolacca americana) antiviral protein (PAP) is a glycosidase which inactivates both eukaryotic and prokaryotic ribosomes. Due to this activity the wild-type PAP gene encoding mature protein has not so far been expressed in Escherichia coli. In spite of the ribosome impairing activity of the pre-PAP (containing two signal peptides at both termini) on bacterial ribosomes in vitro, the full-length PAP gene has been expressed successfully, although at a low level in E. coli under an inducible lac promoter. In this study we show that the full-length PAP gene, but not the PAP gene devoid of the N-terminal signal peptide codons, can be expressed constitutively in E. coli cells to produce a much higher yield as compared with the inducible expression. The full-length PAP is biologically active and it accumulates as inclusion bodies in bacterial cytoplasm. RNA analysis together with protein measurements show that the PAP gene is poorly transcribed and the PAP mRNA is poorly translated when a lac operator sequence is placed in front of the Shine/Dalgarno (SD) sequence. Nucleotide folding analysis of the 5' untranslated mRNA revealed that the SD sequence in the presence of a lac operator is involved in a stable secondary structure, whereas it is more relaxed in the mRNA transcribed from the constitutive vector. These results provide evidence that the low expression level of full-length PAP gene is due to inefficient transcription and translation but not to the toxicity of the expressed PAP.

Gene expression evidence indicates that nucleotides 507-513 and 1434-1440 in 16S rRNA are organized in close proximity on the Escherichia coli 30S ribosomal subunit

A non-Shine-Dalgamo translational initiator is identified in Escherichia coli. The nucleotide sequence ACCUACUCGAGUUAG, designated as PL, is capable of initiating translation of pokeweed antiviral protein (PAP) and human calcitonin (hCT) mRNAs in E. coli cells. The yield of recombinant protein was double that obtained with the consensus Shine-Dalgarno-sequence-(SD)-driven translation. The PL sequence is composed of two heptanucleotides (ACCUACU, box I and GAGUUAG, box II) which are complementary to nucleotides 1434-1440 and 507-513, respectively, in 16S rRNA. Mutational analysis shows that the translation initiation efficiency with either box alone is much lower than that obtained with the entire PL sequence, indicating that the boxes interact simultaneously with both complementary regions in 16S rRNA during the translation initiation step. Based on these results, we propose that the two widely separated regions 507-513 (part of helical domain 18) and 1434-1440 (belonging to helical domain 44) are organized in close proximity to each other and to the ribosome decoding center on the surface of the E. coli 30S ribosomal subunit.

Does the epsilon sequence of phage T7 function as an initiator for the translation of CAT mRNA in Escherichia coli?

Epsilon (epsilon) sequence [UUAACUUUA, complementary to nucleotides 458-466 of the 16S ribosomal RNA (rRNA)] which is naturally occurring at the 5'-untranslated leader of phage T7 gene 10 mRNA was originally described as a powerful translational enhancer in Escherichia coli. Recent studies with this sequence led to controversial conclusions about its translational initiation and enhancing capability. In this study different sequence derivatives of epsilon were constructed to evaluate its efficiency not only to enhance translation of the chloramphenicol acetyltransferase (CAT) mRNA in E. coli, but also to function as an independent initiator of translation. It was observed that the epsilon sequence in combination with the CAT natural Shine-Dalgarno (SDn) or the SD consensus sequences enhanced, as expected, the translation of CAT mRNA. The natural epsilon sequence without an SD sequence failed to initiate or enhance the translation of CAT mRNA. However, when the complementarity of epsilon to 16S rRNA was increased from 9 to 16 nucleotides, epsilon alone (without the SD sequence) became an independent translational initiator with an efficiency of about 80% that obtained with the SD consensus sequence.

Unusual effect of clusters of rare arginine (AGG) codons on the expression of human interferon alpha 1 gene in Escherichia coli

The human interferon (hIFN alpha 1) gene contains 11 arginine (Arg) codons AGG or AGA, which are extremely rare for bacteria, four of which are organized in tandems. The two AGG tandems (corresponding to Arg12 Arg13 and Arg163 Arg164) are known to inhibit the translation of hIFN alpha 1 mRNA and therefore they are considered to be responsible for the poor expression of hIFN alpha 1 gene in bacterial cells. To study the effect of these two tandems on the expression of hIFN alpha 1 in E. coli, four new gene variants were designed to contain preferential Arg codons (CGT) substituted for the rare AGG codons in either the first, the second or both AGG tandems. We found that, whereas the yield of hIFN alpha 1 protein per cell remained unchanged, the level of hIFN alpha 1 mRNA decreased gradually (by a factor of two) with the consecutive substitution of the first, second and both AGG tandems. These results indicated, first, that the AGG clusters might have a stabilizing effect on the mRNA, and second, that mRNAs devoid of such clusters were translated at a higher rate in vivo. The protein products of the four genes (having the same amino acid sequence) showed different specific antiviral activity. The most active was the product of gene hIFN alpha 1(c) in which the second AGG tandem (corresponding to Arg163, Arg164) was preserved while the least active was the protein of gene hIFN alpha 1(d) (devoid of both AGG clusters). The role of the AGG tandems in folding of the gene product is discussed.

Fluorescence spectral characteristics of novel asymmetric monomethine cyanine dyes in nucleic acid solutions

Six new asymmetric monomethine cyanine dyes have been synthesized and their fluorescence characteristics in the presence of nucleic acids studied. The new dyes have no fluorescence of their own in water solutions upon excitation at 480 nm but they become strongly fluorescent in the presence of nucleic acids. The fluorescence maxima of the investigated dyes are found at 525-545 nm when bound to dsDNA and around 600 nm upon binding to RNA and ssDNA. Fluorescence quenching studies with increasing concentrations of NaCl indicate that the cyanine dyes have a mixed (intercalating and groove binding) type of interaction with dsDNA.

Comparative study on the effect of signal peptide codons and arginine codons on the expression of human interferon-alpha 1 gene in Escherichia coli

Human interferon-alpha 1 (HuIFN-alpha 1) gene containing signal peptide codons is poorly expressed in bacteria, and this is explained by the presence of clusters of rare (AGG) arginine codons in its structure. In this study, we have constructed a series of modified HuIFN-alpha 1 genes to study the effect of both residual signal peptide codons and clusters of AGG codons on gene expression in Escherichia coli cells. Our results showed that substitution of preferential for rare arginine codons in two clusters did not affect the yield, whereas deletion of the signal peptide codons led to a 10-fold increase in the yield of recombinant protein. To understand the mechanism of interference of gene structure on the expression of the HuIFN-alpha 1 gene in vivo, both the level and stability of HuIFN-alpha 1 mRNA were measured. The amount of HuIFN mRNA increased almost five times on deletion of the signal peptide codons from HuIFN-alpha 1 gene constructs (containing AGG clusters or not). The stability of mRNA obtained from all gene constructs was shown to be the same (half-life of 60 +/- 5 secs), indicating that the signal peptide codons interfere with both the efficiency of transcription of the HuIFN-alpha 1 gene and translation of its mRNA.

A second putative mRNA binding site on the Escherichia coli ribosome

Translation in bacteria is initiated by a base-pairing interaction between the extreme 3'-end of the small-subunit rRNA and a purine-rich domain (Shine-Dalgarno (SD) sequence) preceding the initiation codon at the 5'-end of most bacterial mRNAs. Here, we describe the identification of a second functional and alternative site on the Escherichia coli ribosome which is capable of interacting with mRNA devoid of SD sequences and initiate the translation. This site is localized between nt 1340 and 1360 of the 16S rRNA in E. coli and is complementary to the untranslated region at the 5'-end of tobacco mosaic virus RNA (omega sequence).

Expression of human alpha 1 interferon genes in vectors containing tandemly located promoters recognized by two different RNA polymerases (Escherichia coli and T7)

An expression vector containing two tandemly located promoters (T7 and P1) and two transcription terminators recognized by two different RNA polymerases (T7 RNA polymerase and Escherichia coli RNA polymerase) was constructed. Human alpha 1 interferon gene variants were cloned in this vector and their expression was studied in E. coli strains containing [E. coli BL2I (DE3)] or devoid (E. coli BL21) of the gene for the T7 RNA polymerase. We report that simultaneous activity of the two promoters reduces the level of gene expression when compared with the levels of expression corresponding to either P1 or T7 promoter alone.

Porcine granulosa cell conditioned media as autocrine regulator of progesterone secretion

The ability of porcine granulosa cells to release a progesterone inhibiting substance(s) was examined in vitro. Granulosa cells (SGCs, MGCs and LGCs) were harvested from small, medium or large antral follicles respectively. The effect of granulosa cell conditioned media obtained from small follicles (SGCCM) was studied in the culture of LGCs by estimation of progesterone secretion; the conditioned media evoked the inhibition of progesterone secretion by the LGCs. SGCCM produced by various numbers of cultured granulosa cells showed a dose-related inhibition of progesterone production. A maximum inhibitory effect was noted when a 5-fold concentration of SGCCM was used. The addition of SGCCM had no effect on the growth of the cultured cells. The factor(s) inhibiting progesterone secretion appeared to be a nonsteroidal substance of molecular mass greater than 10 kDa and was heat-stable and trypsin-sensitive. The data presented support the suggestion that the conditioned media generated by primary cultures of SGCs contain nonsteroidal regulators capable of inhibiting progesterone secretion by cultured LGCs; this inhibitory activity can play an important autocrine regulatory role in the process of follicular differentiation.

Effect of formaldehyde on the efficiency of hybridization of DNA immobilized on nitrocellulose filters

We report in this study that under certain conditions formaldehyde interacts with DNA and makes it more efficient for hybridization on nitrocellulose filters. Hybridization signals of formaldehyde-treated DNA are stronger (up to 10 fold) as compared with that of the heat- or alkali-denatured DNA. Various parameters of the DNA-formaldehyde reaction are optimized as follows: (a) 6 x SSC, 10% formaldehyde, 60 degrees C, 20-30 min, reaction volume 10-200 microliters or (b) 6 x SSC, 5% formaldehyde, 98 degrees C, 15 min, reaction volume 10-200 microliters. Treatment of agarose gels after electrophoresis with formaldehyde improved both the transfer of DNA and the efficiency of hybridization. The following conditions are recommended for gel treatment: denaturation in 0.3 N NaOH, 1 M NaCl followed by neutralization with 0.5 M phosphate buffer, pH 7.0, containing 10% formaldehyde at 60 degrees C for 20 min.

Efficiency of the 5'-terminal sequence (omega) of tobacco mosaic virus RNA for the initiation of eukaryotic gene translation in Escherichia coli

Recent studies have demonstrated that the 5' leader (omega sequence) of tobacco mosaic virus RNA has a certain enhancing capacity for translation of mRNA in both prokaryotes and eukaryotes. In order to estimate the efficiency of omega to initiate translation of mRNA in Escherichia coli, in comparison to the Shine-Dalgarno (S/D) sequence, we have inserted eight different eukaryotic genes into two types of E. coli expression vectors containing one constitutive promoter (P1) but different translation-initiation sites (S/D or omega delta 3 sequence, respectively). The efficiency of transcription and translation in vivo was evaluated for these vectors by measuring the yield of protein and both the level and stability of mRNA. We report that substitution of omega delta 3 for S/D decreases the yield of expressed protein 4-1900-fold and the content of gene-specific mRNA is decreased by about sevenfold. However, in comparison with the S/D sequence, the level of protein expressed under the translational control of omega delta 3 is less sensitive to changes in the 5' coding region. We also report that the omega sequence contains a region of 10-12 nucleotides complementary to the small ribosomal subunit RNA (rRNA) of E. coli, Eikenella corrodens and Xenopus laevis, and to the rRNA of the (small ribosomal) subunit of Oryza sativa.

Shotgun concatenation of synthetic genes: construction of concatemeric human calcitonin genes

A new fast and reliable approach for construction of concatemeric synthetic genes is described. The method consists of shotgun polymerization of three truncated monomeric gene units using a specific linker, followed by cloning of the recombinant clones and screening them for the presence of concatemeric genes of defined length. The method is illustrated by constructing a series of tandemly repeated human calcitonin (hCT) genes.

Type A oncornavirus-like particles in turkey bone marrow cells transformed by avian leukemia virus

Type A oncornavirus-like particles (TAOLP) were found in the cytoplasm of turkey bone marrow cells transformed by strain Mc-31 avian leukemia virus. They resembled morphologically the cores of budding virions and the cores of immature extracellular Mc-31 virus particles. TAOLP were observed more often in T3Mc31 cells where cytopathological changes existed. TAOLP were not found in the materials from in vivo experiments. A relationship is likely to exist between TAOLP and Mc-31 virus and TAOLP could represent a side product of Mc-31 virus replication.

Determination of plasmid copy number by the "boiling" method

A fast and reliable approach for determination of plasmid copy number in Escherichia coli is proposed, based on the "boiling" method (5) for separation of plasmid and chromosomal DNA. The method includes in vivo uniform labeling of total bacterial DNA, separation of DNA into plasmid and chromosomal DNA fractions, and quantitation of DNA in the two fractions by radioactivity measurement. No isolation and purification of native DNA are necessary.

Sequence heterogeneity of the human alphoid satellite DNA and thermal stability of mismatched alphoid DNA duplexes

1. 340 bp (dimer) and 680 bp (tetramer) fractions of the human alphoid satellite DNA (h alpha RI DNA) were isolated after complete cleavage of total human DNA with EcoR I and cloned in pBR 32.5. 2. Ten clones containing 340 bp inserts and one clone containing 680 bp insert were sequenced in order to investigate the sequence heterogeneity of this satellite DNA and the sequence data were compared with the consensus h alpha RI DNA sequence of Wu and Manuelidis (1980). 3. It was shown that in all clones studied the mutations are nonrandomly distributed along the human alphoid monomers forming distinct conservative and variable regions. 4. This mutation distribution pattern was compared with the nucleotide variations between the consensus sequences of different primate alphoid DNAs and it was found that the interspecies nucleotide divergency of this satellite DNA is quite similar to the intragenomic one. 5. The sequenced h alpha RI DNA clones were used for preparation of DNA-DNA hybrids with a known percentage of base pair mismatching. 6. These hybrids were melted on hydroxyapatite (HAP) and the results obtained were used to determine the relationship between the thermal stability (Tm) and the extent of base pair mismatching for naturally diverged DNA sequences. 7. A value of 0.7 degrees C decrease in Tm per 1% base pair mismatching was found.

Radioiodination of naturally occurring phospholipids

A simple and rapid nonenzymatic method for radioiodination of phospholipids is described. It involves oxidation of Na125I with TlCl3 (or chloramine-T) in an aqueous medium, with subsequent exposure of the phospholipids, dissolved in chloroform/methanol, to the action of the oxidizing mixture. Purification of the radiolabelled phospholipids was effected by washing with sodium thiosulphate followed by thin-layer chromatography on silica gel. Specific radioactivity of 125I-labelled phosphatidylcholine was estimated to be about 10 muCi/mg phospholipid. The method is designed for radioiodination of various naturally occurring phospholipids.

Does the concentration of DNA (Co) and the time of incubation (t) as parameters of Cot influence the thermal stability of the DNA duplexes?

It has been shown in a previous paper (8) that the prime product of reassociation of related DNA sequences under open experimental conditions are mismatched duplexes which undergo 'maturation' upon further incubation. Due to this feature, the Tm value of the duplexes of a large number of DNAs is strongly dependent on the Cot value. Here we present data showing that the Tm of the duplexes of such type of DNAs depends also on the concentration of DNA in the range of one and the same Cot value. The significance of this finding in studying the taxonomic relationship by DNA-DNA hybridisation is discussed.

Large scale purification of plasmid DNA

A simple and rapid procedure for large scale purification of plasmid DNA is described. The procedure consists of two main steps: 1. Alkaline extraction of plasmid DNA (by a slight modification of the method of Birnboim and Doly (1)) and 2. Purification of the crude extract by hydroxyapatite chromatography. The plasmids obtained are biologically active and can be used in gene manipulation experiments.

Histone acetylation in chromatin containing mouse satellite DNA

Histone acetylation in transcriptionally inactive chromatin has been studied with chromatin containing mouse satellite DNA. The latter was obtained by digestion of nuclei from Ehrlich ascites tumor cells with the restriction nuclease Bsp, which degrades main-band DNA but leaves satellite DNA intact. The enzyme-resistant material was separated by gel filtration. Satellite DNA amounted to 65% of the total DNA in this fraction. When the cells were grown in the presence of sodium n-butyrate to inhibit histone deacetylation, a few, if any, hyperacetylated forms of core histones were found in satellite chromatin. Conversely, the highest quantity of tetraacetylated H4 molecules was found in the fractions containing the most extensively degraded chromatin.

Interaction of homo-aza-steroidal ester of [p-[bis-(2-chloroethyl) amino]phenyl]acetic acid (ASE) with DNA of Ehrlich ascites tumor cells

A cytostatic, homo-aza-steroidal ester of [p-[bis-(2-chloroethyl) amino]phenyl]acetic acid (ASE) was reduced with NaB3H4 and [3H]ASE-treated DNA prepared in vitro. We found that: (1) ASE reacts preferentially with purines; (2) ASE decreases the thermal stability of the double helix upon binding to DNA; (3) [3H]ASE binding sites are clustered along the DNA molecules; (4) ASE binding sites probably represent oligo- or polypurine sequences.

EPR study on the interaction of spin-labelled hydrazine mustard derivatives with DNA

The interaction of three spin-labelled compounds, derivatives of bis-(2-chloroethyl)-hydrazine (HMSL), N-methyl,N-chloroethyl-hydrazine (MCEHSL) and bis-(2-bromoethyl)-hydrazine (BEHSL) with DNA was studied by the method of electron paramagnetic resonance (EPR). It was found that HMSL (containing two chloroethyl groups) and MCEHSL (containing one chloroethyl group) gave spin-labelled dsDNA with identical strongly immobilized EPR spectra. The conclusion was drawn that only one of the alkylating groups of HMSL reacted with DNA. In contrast, the EPR spectrum of DNA spin-labelled with BEHSL was non-immobilized due to the strong destabilizing effect of this compound on the double helix. The extent of alkylation of DNA with the three hydrazine mustard derivatives was one and the same. It was found, however, that chloroethyl-containing derivatives (HMSL and MCEHSL) had an expressed base specificity and alkylated preferably the guanilic residues, and their bromo-analogue (BEHSL) did not show any base specificity and alkylated the bases of DNA at random.

[Fractionation of chromatin of liver cell nuclei after mild micrococcal nuclease digestion]

Mild micrococcal nuclease treatment of rat and mouse nuclei and fractionation were based on the method of Tata and Baker. Three chromatin fractions, S, P1, P2, were separated, and for each of these fractions the sensitivity to the DNase 1 action was determined. The relative content in these fractions of non-transcribed DNA sequences was established by hydridization with a mouse satellite DNA, and the relative content of transcribed DNA sequences--by hydridization with DNA synthesised on the total poly (A) mRNA. None of the fractions displayed the properties characteristic of active chromatin.

On the heterogeneity of the slow reassociating ("unique") DNA

The slow reassociating fraction of mouse DNA ("unique DNA"), when allowed to reassociate in 0.14 M sodoum phosphate buffer at 50 degrees C showed a biphasic melting curve with a transition at 78--80 degrees C. On the basis of this feature, the slow reassociating DNA was separated preparatively into two fractions: "unique DNA" I and II. Their duplexes showed differences with respect to thermal stability, S1 nuclease resistance and rate of reassociation. About one third of the sequences in each fraction were fraction-specific. The conclusion was drawn that for "unique DNA" I these should be the low repetitive or single copy related sequences (multigene families) and for "unique DNA" II--the unrelated single copy sequences or recent families of low repetitive not yet diverged sequences.

RNA - DNA hybridization on membrane filters with fragmented mammalian DNA

The possibilities of using fragmented mammalian DNA for hybridization on membrane filters were investigated. The adsorption and release of fragmented DNA were studied as influenced by various factors of the hybridization procedure. It was found that working with preparations sufficiently homogeneous in molecular weight with fragment size 4.8-6.5 S, dissolved in 6 times SSC at neutral pH, the adsorption on filters was almost 100%. After incubation of filters for 18 h in 2 times SSC at 65 degrees C about 50% of the fragmented DNA and 20% of the high molecular weight DNA were released. The degree of release differed for the different families of repeated DNA sequences. Lowest release was obtained with the highly repeated DNA (20%) and highest with the unique DNA (63%), i.e. the release was inversely proportional to the renaturation rate of DNA. In the course of release of fragmented total DNA the material remaining on the filters became enriched in highly repeated sequences, due to selective release of the slowly reassociating fractions. As a result, the percentage of fragmented DNA which hybridized with heterogeneous nuclear RNA was higher than that of high molecular weight DNA. The thermal stabilities of the hybrids with fragmented and high molecular weight DNA were identical. The conditions are defined which permit application of the membrane filter hybridization technique to fragmented mammalian DNA.

Isolation of DNA from yeast by chromatography on hydroxyapatite

A simple procedure is described for isolation of purified non degraded total DNA from yeast cells. The procedure involves conversion of the cells into spheroplasts by enzymatic treatment, lysis of the spheroplasts in 8 M urea - 0.24 M sodium phosphate buffer - 0.01 M EDTA (ethylendiamintetraacetic acid, sodium salt) - 1% SDS (sodium dodecyl sulphate), deproteinization of the lysate with chloroform-phenol and separation of the DNA from proteins, RNA and other contaminants by hydroxyapatite chromatography. The yield is about 90% of the DNA in the starting material (spheroplasts).