In vivo post-translational processing and subunit reconstitution of cephalosporin acylase from Pseudomonas sp. 130

Cephalosporin acylases are a group of enzymes that hydrolyze cephalosporin C (CPC) and/or glutaryl 7-amino cephalosporanic acid (GL-7ACA) to produce 7-amino cephalosporanic acid (7-ACA). The acylase from Pseudomonas sp. 130 (CA-130) is highly active on GL-7ACA and glutaryl 7-aminodesacetoxycephalosporanic acid (GL-7ADCA), but much less active on CPC and penicillin G. The gene encoding the enzyme is expressed as a precursor polypeptide consisting of a signal peptide followed by alpha- and beta-subunits, which are separated by a spacer peptide. Removing the signal peptide has little effect on precursor processing or enzyme activity. Substitution of the first residue of the beta-subunit, Ser, results in a complete loss of enzyme activity, and substitution of the last residue of the spacer, Gly, leads to an inactive and unprocessed precursor. The precursor is supposed to be processed autocatalytically, probably intramolecularly. The two subunits of the acylase, which separately are inactive, can generate enzyme activity when coexpressed in Escherichia coli. Data on this and other related acylases indicate that the cephalosporin acylases may belong to a novel class of enzymes (N-terminal nucleophile hydrolases) described recently.

Discovery of a small molecule insulin mimetic with antidiabetic activity in mice

Insulin elicits a spectrum of biological responses by binding to its cell surface receptor. In a screen for small molecules that activate the human insulin receptor tyrosine kinase, a nonpeptidyl fungal metabolite (L-783,281) was identified that acted as an insulin mimetic in several biochemical and cellular assays. The compound was selective for insulin receptor versus insulin-like growth factor I (IGFI) receptor and other receptor tyrosine kinases. Oral administration of L-783,281 to two mouse models of diabetes resulted in significant lowering in blood glucose levels. These results demonstrate the feasibility of discovering novel insulin receptor activators that may lead to new therapies for diabetes.

Improved reporter strain for monitoring Cre recombinase-mediated DNA excisions in mice

Effective use of conditional Cre recombinase-loxP gene modification requires Cre-expressing mouse strains with defined patterns of expression. To assess the in vivo functionality of Cre-expressing mice, we have engineered an improved reporter strain for monitoring Cre-mediated excisions. The beta-galactosidase-neomycin phosphotransferase fusion gene (betageo)-trapped ROSA26 locus was modified by gene targeting such that betageo is expressed only after Cre-mediated excision of loxP-flanked DNA sequences. betageo from the excised ROSA26 allele is expressed ubiquitously in embryos and adult mice. By mating the reporter strain with Cre-expressing transgenic mice, we have shown that the loxP-flanked ROSA26 allele is accessible to Cre during early embryogenesis, as well as in a specific hematopoietic lineage (T lymphocytes). This improved reporter strain should facilitate monitoring in vivo Cre-mediated excision events in a variety of experimental contexts.

Characterization of a neuronal kappaB-binding factor distinct from NF-kappaB

Transcription factors that bind kappaB enhancer elements have begun to garner wide attention in neurobiology. Data suggest that activation of kappaB-binding factors in neurons can be protective against various neurotoxins, but other data have connected NF-kappaB to cell death. In electrophoretic mobility shift assays of kappaB-binding activity, we have found that the predominant activity in rat brain tissue, in primary neurons, and in neuronal cell lines has a mobility inconsistent with that of bona fide NF-kappaB (RelA-p50 heterodimer). We have tentatively termed this activity neuronal kappaB-binding factor (NKBF). Competition assays with various DNA probes distinguished NKBF from NF-kappaB. Probes that efficiently bind the p50 homodimer were able to compete with a conventional NF-kappaB probe for NKBF binding, but NKBF did not react with antibodies to p50 (or any other known Rel family members). Furthermore, UV-crosslinking indicated that NKBF is composed of two polypeptides of 82 kDa and 27 kDa. Although NKBF activity can be elevated in a manner independent of new macromolecular synthesis, it does not appear to be modulated by IkappaB. Finally, no NF-kappaB was induced by glutamate in highly enriched neuronal cultures, although it was induced in neuron-glia cocultures. These data suggest that the primary kappaB-binding transcription factor in neurons is a novel protein complex distinct from NF-kappaB.

Vascular endothelial growth factor receptor KDR tyrosine kinase activity is increased by autophosphorylation of two activation loop tyrosine residues

Vascular endothelial growth factor is an important physiological regulator of angiogenesis. The function of this endothelial cell selective growth factor is mediated by two homologous tyrosine kinase receptors, fms-like tyrosine kinase 1 (Flt-1) and kinase domain receptor (KDR). Although the functional consequence of vascular endothelial growth factor binding to the Flt-1 receptor is not fully understood, it is well established that mitogenic signaling is mediated by KDR. Upon sequencing several independent cDNA clones spanning the cytoplasmic region of human KDR, we identified and confirmed the identity of a functionally required valine at position 848 in the ATP binding site, rather than the previously reported glutamic acid residue, which corresponds to an inactive tyrosine kinase. The cytoplasmic domain of recombinant native KDR, expressed as a glutathione S-transferase fusion protein, can undergo autophosphorylation in the presence of ATP. In addition, the kinase activity can be substantially increased by autophosphorylation at physiologic ATP concentrations. Mutation analysis indicates that both tyrosine residues 1054 and 1059 are required for activation, which is a consequence of an increased affinity for both ATP and the peptide substrate and has no effect on kcat, the intrinsic catalytic activity of the enzyme. KDR kinase catalyzes phosphotransfer by formation of a ternary complex with ATP and the peptide substrate. We demonstrate that tyrosine kinase antagonists can preferentially inhibit either the unactivated or activated form of the enzyme.

Genetic aberrations in glioblastoma multiforme: translocation of chromosome 10 in an O-2A-like cell line

We have examined the genetic aberrations in two near-diploid glioblastoma multiforme cell lines that appear to have arisen from different glial lineages. One cell line, Hu-O-2A/Gb1, expresses antigens and metabolic profiles characteristic of the oligodendrocyte-type-2 astrocyte (0-2A) lineage of the rat central nervous system. This line generates, in vitro, cells with characteristics of 0-2A progenitor cells, oligodendrocytes and astrocytes. The second cell line, IN1434, is derived from an astrocyte or a precursor cell restricted to astrocytic differentiation. In Hu-O-2A/Gb1 the sole homologue of chromosome 10 is disrupted at band 10p11-12.1 by translocation with chromosomes X and 15. The translocation breakpoint is localized between genetic markers D10S2103 and [D10S637, D10S1962, D10S355]. Other aberrations include a 5;14 translocation, deletion of the long and short arms of chromosome 16 and loss of one copy of the CDKN2 gene. IN1434 cells share some cytogenetic abnormalities with Hu-O-2A/Gb1 cells, despite their apparent derivation from a different biological origin, but also have translocations involving the long and short arms of chromosome 1 and the long arm of chromosome 7, and deletion of chromosome 13 at bands 13q12-21.

[A new cultivated technique of Rehmannia glutinosa by sprout cutting]

The traditional cultivated method of Rehmannia glutinosa is the asexual reproduction that small rhizomes are used as materials of reproduction. In this test, the small rhizomes germinated on seedbed, then young sprouts were picked for culture.

Alleletyping of an oligodendrocyte-type-2 astrocyte lineage derive from a human glioblastoma multiforme

We have conducted alleletyping of two novel cell lines derived from glioblastoma multiforme, which appear to have arisen from different glial lineages, by using 76 fluorescently labeled oligonucleotide primers amplifying microsatellite loci covering the entire human genome. One cell line, Hu-O-2A/Gb1, expresses antigens and metabolic profiles characteristic of the oligodendrocyte-type-2 astrocyte (0-2A) lineage of the rat central nervous system. This cell line generated, in vitro, cells with characteristics of 0-2A progenitor cells, oligodendrocytes and astrocytes. The second cell line, IN1434, is derived from an astrocyte or a precursor cell restricted to astrocytic differentiation. Hu-O-2A/Gbl cells show allelic losses of loci on chromosomes 2, 5, 6, 7, 8, 9, 10, 11, 13, 15, 16, 17, 20 and 21. IN1434 cells are likely to have allelic losses of loci on chromosomes 1, 3, 8 and 10, although no control DNA is available for this cell line. These results, for the first time, provide a detailed information of the molecular genetic defects occurring in Hu-O-2A/Gb1 and IN1434.

[Microscopic identification of Herba Dianthi grown in Shandong]

The medicinal materials of four species and two varieties of Herba Dianthi grown in Shandong were identified. The result shows that they are identified easily and accurately according to the outer properties, and they are apparently divided into the Shizhu group, the Qumai group and the Dianthus shandongensis on the basis of their morphological and structural characteristics of the stem and leaf, but they have not obvious distinction among the species of every group.

Quantitative proton magnetic resonance spectroscopy of childhood adrenoleukodystrophy

Cerebral metabolic disturbances in patients with childhood adrenoleukodystrophy (ALD) were assessed by quantitative localized proton MRS. Patient monitoring by follow-up MRS studies served to identify putative markers for disease onset and progression. Whereas normal-appearing white matter of neurologically asymptomatic patients is characterized by slightly elevated concentrations of choline-containing compounds (Cho), an increase of both Cho and myo-inositol (Ins) seems to indicate the onset of demyelination. Markedly elevated concentrations of Cho, Ins, and glutamine in affected white matter reflect active demyelination and glial proliferation. A simultaneous reduction of the concentrations of N-acetylaspartate and glutamate is consistent with neuronal damage or loss. The observation of elevated lactate is in line with inflammation and/or macrophage infiltration. The more severe metabolic disturbances in cerebral ALD correspond to progressive demyelination, neuroaxonal loss and gliosis leading to clinical deterioration and eventually death. The detection of MRS abnormalities before the onset of neurological symptoms may help in the selection of patients for bone marrow transplantation (BMT). Stabilization and partial reversal of metabolic abnormalities is demonstrated in a patient after BMT.

Chinese geneticists' views of ethical issues in genetic testing and screening: evidence for eugenics in China

To identify Chinese geneticists' views of ethical issues in genetic testing and screening, a national survey was conducted. Of 402 Chinese geneticists asked to participate, 255 (63%) returned by mail anonymous questionnaires. The majority of respondents thought that genetic testing should be offered in the workplace for alpha-antitrypsin deficiency (95%) and the predisposition of executives to heart disease, cancer, and diabetes (94%); that genetic testing should be included in preemployment physical examinations (86%); that governments should require premarital carrier tests (86%), newborn screening for sickle cell (77%), and Duchenne muscular dystrophy (71%); and that children should be tested for genes for late-onset disorders such as Huntington disease (85%), susceptibility to cancers (85%), familial hypercholesterolemia (84%), alcoholism (69%), and Alzheimer disease (61%). Most believed that partners should know each other's genetic status before marriage (92%), that carriers of the same defective gene should not mate with each other (91%), and that women should have a prenatal diagnosis if medically indicated (91%). The majority said that in China decisions about family planning were shared by the couple (82%). More than half had views that, in China, there were no laws to prohibit disability discrimination (64%), particularly to protect people with adult polycystic kidney disease (57%), cystic fibrosis (56%), or genetic predisposition to other diseases (50%). To some extent, these results might provide a basis for a discussion of eugenics in China, particularly about China's Maternal and Infant Health Care Law (1994).

Paracrine expression of a native soluble vascular endothelial growth factor receptor inhibits tumor growth, metastasis, and mortality rate

Vascular endothelial growth factor (VEGF) is a potent and selective vascular endothelial cell mitogen and angiogenic factor. VEGF expression is elevated in a wide variety of solid tumors and is thought to support their growth by enhancing tumor neovascularization. To block VEGF-dependent angiogenesis, tumor cells were transfected with cDNA encoding the native soluble FLT-1 (sFLT-1) truncated VEGF receptor which can function both by sequestering VEGF and, in a dominant negative fashion, by forming inactive heterodimers with membrane-spanning VEGF receptors. Transient transfection of HT-1080 human fibrosarcoma cells with a gene encoding sFLT-1 significantly inhibited their implantation and growth in the lungs of nude mice following i.v. injection and their growth as nodules from cells injected s.c. High sFLT-1 expressing stably transfected HT-1080 clones grew even slower as s.c. tumors. Finally, survival was significantly prolonged in mice injected intracranially with human glioblastoma cells stably transfected with the sflt-1 gene. The ability of sFLT-1 protein to inhibit tumor growth is presumably attributable to its paracrine inhibition of tumor angiogenesis in vivo, since it did not affect tumor cell mitogenesis in vitro. These results not only support VEGF receptors as antiangiogenic targets but also demonstrate that sflt-1 gene therapy might be a feasible approach for inhibiting tumor angiogenesis and growth.

[Ultra-morphological study on the surface of the stem and leaf of the original plant of herba Dianthi in Shandong]

Ultra-morphology of 4 spieces and 2 varities of the original plant of Herba Dianthi grown in Shandong was identified with SEM. The result showed that they were aparently divided into the Shizhu group and the Qumai group, and the Dianthus shandongensis was between the two groups, on the basis of the cutin-grain type of the epidermis of the stem and leaf as well as the surface of the guard cell of the stoma.

Accelerated mRNA decay in conditional mutants of yeast mRNA capping enzyme

Current models of mRNA decay in yeast posit that 3' deadenylation precedes enzymatic removal of the 5' cap, which then exposes the naked end to 5' exonuclease action. Here, we analyzed gene expression in Saccharomyces cerevisiae cells bearing conditional mutations of Ceg1 (capping enzyme), a 52 kDa protein that transfers GMP from GTP to the 5' end of mRNA to form the GpppN cap structure. Shift of ceg1 mutants to restrictive temperature elicited a rapid decline in the rate of protein synthesis, which correlated with a sharp reduction in the steady-state levels of multiple individual mRNAs. ceg1 mutations prevented the accumulation of SSA1 and SSA4 mRNAs that were newly synthesized at the restrictive temperature. Uncapped poly(A)+ SSA4 mRNA accumulated in cells lacking the 5' exoribonuclease Xrn1. These findings provide genetic evidence for the long-held idea that the cap guanylate is critical for mRNA stability. The deadenylation-decapping-degradation pathway appears to be short-circuited when Ceg1 is inactivated.

Neuroprotection by dehydroepiandrosterone-sulfate: role of an NFkappaB-like factor

Levels of dehydroepiandrosterone (DHEA) and its sulfated derivative (DHEA-S) decline during aging and reach even lower levels in Alzheimer's disease (AD). Previously published effects of DHEA and DHEA-S on unchallenged neuronal survival led us to test them in an excitotoxicity paradigm. While DHEA-S protected hippocampal neurons against glutamate, little protection was observed with equivalent doses of DHEA itself. This differential neuroprotection was consistent with the ability of DHEA-S (but not DHEA) to elevate a kappaB-dependent transcription factor activity, a phenomenon we previously have connected with neuroprotection. Furthermore, suppression of kappaB DNA-binding by 'decoy' oligonucleotides blocked the neuroprotective activity of DHEA-S. These findings imply that age-related declines in the availability of DHEA-S could exacerbate neurotoxicity, and the data suggest that therapeutic gains may be obtained with pharmacological manipulation of kappaB-dependent transcription in neurons.

[Nucleotide sequence analysis of an antibiotic biosynthesis gene of Streptomyces globisporus]

Antitumor antibiotic C-1027 produced by Streptomyces globisporus has very high biological activity both in vivo and in vitro. Research works showed that one of biosynthesis gene of C-1027 is in the F2 DNA fragment. The plasmid pUC18 was used as vector to subclone the F2 DNA fragment. The nucleotide sequence analysis for F2 DNA fragment was carried out. Results showed that there is an open reading frame encoding for 122 amino acids. According to EMBO and GeneBanks data, this sequence may be a new one.

The LIM-domain binding protein Ldb1 and its partner LMO2 act as negative regulators of erythroid differentiation

The nuclear LIM domain protein LMO2, a T cell oncoprotein, is essential for embryonic erythropoiesis. LIM-only proteins are presumed to act primarily through protein-protein interactions. We, and others, have identified a widely expressed protein, Ldb1, whose C-terminal 76-residues are sufficient to mediate interaction with LMO2. In murine erythroleukemia cells, the endogenous Lbd1 and LMO2 proteins exist in a stable complex, whose binding affinity appears greater than that between LMO2 and the bHLH transcription factor SCL. However, Ldb1, LMO2, and SCL/E12 can assemble as a multiprotein complex on a consensus SCL binding site. Like LMO2, the Ldb1 gene is expressed in fetal liver and erythroid cell lines. Forced expression of Ldb1 in G1ER proerythroblast cells inhibited cellular maturation, a finding compatible with the decrease in Ldb1 gene expression that normally occurs during erythroid differentiation. Overexpression of the LMO2 gene also inhibited erythroid differentiation. Our studies demonstrate a function for Ldb1 in hemopoietic cells and suggest that one role of the Ldb1/LMO2 complex is to maintain erythroid precursors in an immature state.

[Clinical observation on Doula delivery]

OBJECTIVE

To improve the obstetricare quality during labour and delivery, our hospital carried out Doula delivery which is an appropriate technology in promoting natural delivery reported by Dr M Klaus, USA.

METHODS

Mothers were accompanied by senior experienced midwife who afforded continuous physical, psychological and emotional support during the whole course of labour. From April to August 1996, 46 cases of primigravida were selected as study group. Another 336 primigravida given birth in the same period were taken as controls, who were accompanied by their family member during their active phase of labour.

RESULTS

The results showed that the cesarean section rate was 6.5% in Doula group while 20.8% in the control group. The difference was significant (P < 0.05). The duration of labour and volume of postpartum bleeding both declined obviously in the study group (P < 0. 05).

CONCLUSION

Doula delivery offered better quality of health care during labour and decreased cesarean section rate duration of labour and postpartum bleeding.

[The effect of cryotreat on the size of the medium and high melting-point castable alloys]

Castable alloys are widely used in prosthodontics. The properties of alloys can be improved by cryotreat. This method may cause a size alteration of materials. This study revealed the effects of different cooling rates on the size of the castable alloys. The results showed: 1. The rapid cooling rate caused significant deformation of the alloys. 2. The 3 degrees C/min rate and the 1 degree C/min rate did not cause any significant deformation of the alloys. 3. The 3 degrees C/min rate and the 1 degree C/min rate did not show any difference in their deformation causing ability. 4. The rapid cooling rate and the slow cooling rate (3 degrees C/min and 1 degree C/min) showed significant difference in their deformation causing ability. These results suggested that 3 degrees C/min was recommendable as a cooling rate of the cryotreat of the medium and high melting-point castable alloys.

China's genetic services providers' attitudes towards several ethical issues: a cross-cultural survey

Attitudes towards ethical, legal and social issues in genetic research and practice were investigated in 402 genetic services providers from 30 provinces and autonomous regions in China. This was done using a Chinese version of an international survey questionnaire on ethics and genetics that has been circulated in 37 nations. In all, 255 study participants completed questionnaires (63%). The majority of the respondents (89%) reported that they agreed with the current Chinese laws and regulations on termination of pregnancy for genetic abnormalities and non-medical indications, on the basis of considerations of population control and family planning. More than half the respondents opposed sex selection by prenatal diagnosis in the absence of an X-linked disorder. However, most of them (86%) would prefer directive counseling. More than half would agree to disclose genetic information to relatives at risk, and would permit third parties such as law enforcement agencies, spouse/partner, blood relatives, employers involving public safety, life and health insurers to access stored DNA without consent. The majority (73%-98%) also thought that DNA fingerprinting should be required for prisoners convicted of or charged with crimes, members of armed forces and all newborns. Although these are only the first part of the results of our international survey, they provide an initial basis for international discussion on ethics and genetics in China.

[The effect of cryotreat on the mechanical properties of the medium and high melting-point castable alloys]

Two mechanical properties that are closely related to the clinical practice, i.e. the surrendering toughness and the hardness, of the medium and high melting-point castable alloys, were tested before and after the cryotreat. The results showed: 1. Cryotreat significantly increased the surrendering toughness of the medium and high melting-point castable alloys (40.00%); 2. Cryotreat significantly increased the surrendering toughness of the medium and high melting-point castable alloys (25.45%); 3. Cryotreat significantly increased the surrendering modulus of the high melting-point castable alloys (25.77%); 4. Cryotreat significantly increased the hardness of the medium melting-point alloys(24.40%); 5. Cryotreat significantly increased the hardness of the medium melting-point alloys (7.77%). These results suggest that cryotreat is an effective procedure in enhancing the toughness and hardness of the medium and high melting-point castable alloys.

[Packing drainage of transmastoid approach for treatment of otogenic brain abscess: a report of 30 cases]

Thirty cases of patients with otogenic brain abscess (OBA) who received mastoid radical operations were treated simultaneously by means of packing drainage via the appoach of the mastoid operative cavity. 26 cases of those were cured. The results showed that the therapeutical method gave satisfactory effectiveness and had many advantages. It provided an effective montitor for retraction and had many vomica, and gave ample drainage for retraction in that it made OBA seldom recur. The operative procedure is fit for the great majority of OBA. The paper also discussed intraoperative and postoperative complications and other problems pertinent to the operation.

Mutations of O6-methylguanine-DNA methyltransferase gene in esophageal cancer tissues from Northern China

Epidemiologic studies have implicated the involvement of environmental factors in the etiology of esophageal cancer (EC). Our previous data have indicated that EC patients and their blood relatives show genomic instability and are deficient in repair of DNA damage induced by N-nitroso-compounds and related genotoxic agents. Thus, exposure to high levels of N-alkylnitrosamines, which are known animal carcinogens and which induce alkyl adducts in DNA, may be causally linked to EC. Among the alkyl adducts, O6-alkylguanine was shown to be the critical one related to carcinogenic lesions; its repair varies widely in a tissue-specific fashion. O6-methylguanine-DNA methyltransferase (MGMT) is responsible for its repair. Hence, inactivating mutations in this protein would impair the efficiency of the repair process. To screen for possible mutations in the MGMT polypeptide in EC patients, we analyzed a highly conserved region of the MGMT gene in 40 EC tissues and lymphocytes of 6 high-risk EC family members from high EC areas of Northern China by polymerase chain reaction single-strand conformation polymorphism and by direct sequencing of PCR products. Ten base substitutions (point mutations) within 8 codons of 7 EC samples were identified. However, no germline mutation was found in the high EC families studied so far. Concurrent study in 30 pairs of fresh EC tissues and their adjacent normal mucosa by Southern blot and Western blot analyses showed deletion of the MGMT gene in 2 samples. Thus, the high frequency of mutations (7/40) and deletions (2/30) of the MGMT gene may be partially responsible for the overall high mutation rate observed in EC tissues.

[Preliminary observation of MRI manifestations of adult pulmonary tuberculosis]

OBJECTIVE

To study the role of MRI in diagnosis of adult pulmonary tuberculosis.

METHODS

MRI and X-ray appearance of 55 adult pulmonary tuberculosis cases were reviewed.

RESULTS

No obvious difference was found between the images of MRI and chest radiography which reflect infiltrative and proliferative pathologic changes of pulmonary tuberculosis (including cavity, tuberculoma and caserous pneumonitis). Infiltrative, proliferative lesions and caserous pneumonitis showed middle signal on the T1 and T2 weighted images. Cavity showed low signal. Tuberculoma showed generally hyterogenous signal on the T2 weighted images.

CONCLUSION

It is unnecessary to use MRI as a routine tool for diagnosis of pulmonary tuberculosis.

[A three-dimensional finite element stress analysis of implant-supported prosthesis and its supporting tissue in the edentulous mandible. Part 5. The influence of implant type in complete implant overdenture and its supporting tissue]

The stress distribution of implant, implant-bone interface, alveolar ridge surface and the overdenture when supported by cylindrical-type or blade-type implants under three kinds of occlusion, were investigated respectively in this study. The results showed that the extreme principle stress was greater when the denture was supported by blade-type implants than by cylindrical type one. The stress distribution of the system with application of cylindrical type implant is more acceptable.

[A three-dimensional finite element stress analysis of implant-supported prosthesis and its supporting tissue in the edentulous mandible. Part 6. The influence of superstructure in mandibular complete implant overdenture and its supporting tissue]

The effect of superstructure, including telescope, conventional-bar and modified-bar, on the stress distribution of mandibular complete implant overdenture and its supporting tissue was investigated in this study. The results demonstrated that bar could lower the extreme principle stress of the implant, but the stress distribution of implant-bone interface was better when the implants were not linked with each other. Modified-bar is not preferred because it increases the stress of implant and its interface.

FruA, a putative transcription factor essential for the development of Myxococcus xanthus

A new developmental gene, fruA, of Myxococcus xanthus was cloned using a one-step cloning vector, TnV. DNA sequencing of the wild-type allele of the fruA gene indicated that the fruA gene encodes a protein of 229 amino acid residues with a calculated molecular weight of 24672. The deduced amino acid sequence of FruA protein showed similarity to those of many bacterial regulatory proteins carrying a DNA-binding helix-turn-helix motif. The transcription-initiation site of the fruA gene was determined by a primer-extension experiment. Development of M. xanthus cells with a disrupted fruA gene stopped at the stage of mound formation. Although cells were able to aggregate to form mounds, myxospores were not formed. By Northern and Western blot analysis, it was found that the fruA expression was not detected during vegetative growth but initiated at around 6 h and reached the highest level at 12 h after the onset of development. Expression of the fruA gene was dependent on the expression of asg, bsg, csg, dsg, and esg genes, indicating that a series of intercellular signalling is necessary for the expression of the fruA gene. The effects of the fruA mutation on beta-galactosidase expression of various developmentally regulated genes fused with the lacZ gene were analysed; three developmental lacZ fusions (omega 4469, omega 4273 and omega 4500) were either poorly induced or not induced at all, while three other lacZ fusions (omega 4408, omega 4521 and omega 4455) expressed at the early stage of development were normally induced but were unable to be repressed at a later stage of development as in the wild-type strain. Interestingly, in the fruA mutant, tps (the gene for protein S) was not activated. From these results together with analysis of the amino acid sequence of FruA, we propose that FruA is a putative transcription factor required for the development of M.xanthus.

Effect of interferon on 5-fluorouracil-induced perturbations in pools of deoxynucleotide triphosphates and DNA strand breaks

Interferon (IFN) augments the anabolism of 5-fluorouracil (5FU) to its active metabolite, fluorodeoxyuridylate (FdUMP), which inhibits thymidylate synthase (TS). We sought to determine whether this resulted in greater perturbations of nucleotide pools and if so, whether this was associated with an increase in cell lethality, specifically focussing on the lethal cellular lesion, DNA double strand breaks (dsb). To determine whether combination therapy with 5FU + IFN resulted in greater depletion of thymidine nucleotide pools than 5FU alone, a highly sensitive DNA polymerase assay was used. In two human colon cancer cell lines, treatment with 5FU + IFN resulted in a rapid decrease in levels of dTTP by 95%. The addition of IFN to 5FU resulted in greater depletion of dTTP levels over treatment with 5FU alone by up to fourfold, and markedly augmented the dATP/dTTP ratio. The addition of IFN to 5FU had no effect on 5FU-induced perturbations in dCTP, dGTP or dATP pools at 8 and 12 h. Measurement of DNA dsb demonstrated that treatment of HT-29 cells with 10 microM 5FU for 24 h did not increase DNA dsb versus control. The combination of 5FU + 500 U/ml IFN, however, resulted in an increased number of dsb versus both 5FU and untreated control cells (P < 0.01), equivalent to 0.74 +/- 0.12 Gy. The addition of IFN to 5FU resulted in a selective further depletion of pools of dTTP and an increase in the number of DNA dsb versus 5FU treatment alone.

Interferon augments the cytotoxicity of hydroxyurea without enhancing its activity against the M2 subunit of ribonucleotide reductase: effects in wild-type and resistant human colon cancer cells

The effects of prolonged exposure to the ribonucleotide reductase (RR) inhibitor, hydroxyurea (HU), were assessed in the presence or absence of recombinant interferon alfa-2a (IFN) in wild-type human colon cancer cells (HT-29) and variants expressing low-level resistance to HU (R200). IFN at nontoxic concentrations decreased the IC50 of HU from 368 microM to 215 microM (P < 0.01) in wild-type cells, but not in the resistant variants. Potential cellular targets for the HU/IFN interaction were examined. In wild-type, but not resistant cells, treatment with HU at clinically achievable concentrations (1000 microM) resulted in rapid early inhibition of RR activity between 4 and 24 h after treatment with a maximal decrease of 65% at 12 h, decreases in cellular levels of dATP, dCTP and dGTP by 50-90% over the same time course, and a two- to fourfold increase in the level of mRNA for both the M1 and M2 subunits of RR, at 24, but not between 1 and 4 h, which probably represents a response to the earlier decrease in RR activity. IFN at a clinically achievable concentration (500 U/ml) failed to augment the effects of HU on RR protein, RR mRNA levels or RR enzyme activity in either the wild-type or resistant cells, suggesting that the mechanism by which IFN augments the effects of HU in the wild-type cells is independent of the effects of HU on M2.

Vaccinia virus mRNA (guanine-7-)methyltransferase: mutational effects on cap methylation and AdoHcy-dependent photo-cross-linking of the cap to the methyl acceptor site

The (guanine-7-)methyltransferase domain of the vaccinia virus mRNA capping enzyme is composed of the C-terminal portion of the D1 subunit, D1(498-844), heterodimerized with the D12 protein. In order to identify protein structural elements involved in cap methylation, we introduced eight alanine substitution mutations within two sequence motifs of D1(498-844)-(594)VLAIDFGNG(602) and (681)IHYSF(685)--that are conserved in the cap methyltransferase from yeast. The D1(498-844)-Ala proteins were coexpressed in bacteria with the D12 subunit, and the recombinant D1(498-844)/D12 heterodimers were purified. Alanine substitutions at five positions--Asp-598, Gly-602, Ile-681, Ser-684, and Phe-685--had little or no effect on methyltransferase activity. Mutations at three conserved residues were deleterious. Alanine substitution at Gly-600 reduced the specific activity to 4% of that of the wild-type protein. Substitutions at His-682 and Tyr-683 reduced activity to 4% and 0.05%, respectively. By further mutating Tyr-683 to Phe and Ser, we established that the aromatic group was essential for cap methylation, whereas the hydroxyl moiety was dispensable. Specific binding of the methyltransferase to the RNA cap was demonstrated by UV cross-linking to [32P]GMP-labeled capped poly(A). Label transfer occurred exclusively to the D1(498-844) subunit and was competed by the cap analogs GpppA and m7GpppA. Cap-specific cross-linking to m7GpppA(pA)n was stimulated by AdoHcy, whereas cross-linking to GpppA(pA)n was unaffected by AdoHcy, but stimulated by AdoMet. We suggest that occupancy of the methyl donor site either enhances the affinity for the cap guanosine or alters the protein interface so that a photoreactive moiety is brought closer to the cap structure. The catalytically defective H682A, Y683A, and Y683S mutant methyltransferases were unable to cross-link to the cap in the presence of AdoHcy. The catalytically defective G600A mutant did cross-link to the cap in the presence of AdoHcy, suggesting that this mutation affects the chemical step of transmethylation.

Genetic alterations on chromosomes 3 and 9 of esophageal cancer tissues from China

In previous studies, we had demonstrated that allelic losses in esophageal cancer (EC) tissues are frequently involved in chromosomes 3 and 9 and that EC patients and their blood relatives have low capacity to repair damaged DNA and showed genetic instability. To better define the deleted chromosomal loci and understand the genetic instability in EC tissues, we selected 12 microsatellite markers (D3S1232, D3S1238, D3S1289, D3S1480, D3S647, D3S966, D3S1317, D3S659, D9S156, D9S171, D9S176 and GSN) to examine 36 paired EC tissues for loss of heterozygosity (LOH) and microsatellite instability (MIN) on chromosomes 3 and 9. The frequent LOH was found at D9S156(9p21), D3S647(3p23) and D3S1480(3p14.2), implying the possible existence of tumor suppressor genes near the deleted loci. Higher LOH incidence at D9S156 (9/18) and D3S1480 (8/19) was observed in EC tissues from Beijing, a low EC area. More frequent LOH at D3S647 (6/14) was found in EC tissues from Yangquan, a high EC area. This geographic difference of LOH occurrence was indicative of genetic heterogeneity in the etiology of EC. 24 of 36 (66.7%) EC tissues showed MIN at one or more chromosomal loci. The putative EC suppressor genes on chromosomes 3 and 9 and the molecular basis of the genetic instability associated with EC remain to be elucidated.

Mutational analysis of the Saccharomyces cerevisiae ABD1 gene: cap methyltransferase activity is essential for cell growth

RNA (guanine-7-)-methyltransferase is the enzyme responsible for methylating the 5' cap structure of eukaryotic mRNA. The Saccharomyces cerevisiae enzyme is a 436-amino-acid protein encoded by the essential ABD1 gene. In this study, deletion and point mutations in ABD1 were tested for the ability to support growth of an abd1 null strain. Elimination of 109 amino acids from the N terminus had no effect on cell viability, whereas a more extensive N-terminal deletion of 155 residues was lethal, as was a C-terminal deletion of 55 amino acids. Alanine substitution mutations were introduced at eight conserved residues within a 206-amino-acid region of similarity between ABD1 and the methyltransferase domain of the vaccinia virus capping enzyme. ABD1 alleles H253A (encoding a substitution of alanine for histidine at position 253), T282A, E287A, E361A, and Y362A were viable, whereas G174A, D178A, and Y254A were either lethal or severely defective for growth. Alanine-substituted and amino-truncated ABD1 proteins were expressed in bacteria, purified, and tested for cap methyltransferase activity in vitro. Mutations that were viable in yeast cells had either no effect or only a moderate effect on the specific methyltransferase activity of the mutated ABD1 protein, whereas mutations that were deleterious in vivo yielded proteins that were catalytically defective in vitro. These findings substantiate for the first time the long-held presumption that cap methylation is an essential function in eukaryotic cells.

Giant dipole resonance neutron yields produced by electrons as a function of target material and thickness

This paper characterizes the functional dependence of the giant dipole resonance neutron yield produced by electrons in terms of the atomic number (Z) and thickness (T) of the target. The yields were calculated by integrating, over the photon energy, the product of the differential photon track length and published photoneutron cross sections. The EGS4 Monte Carlo code and analytical formulas were used to calculate the differential photon track length. In thick targets, the Giant Dipole Resonance neutron yield approaches a saturation value as target thickness T increases to 10 radiation lengths. A formula, 8 x 10(-6) x (Z1/2 + 0.12 Z3/2 - 0.001 Z5/2) n electron-1 MeV-1, developed from EGS4 calculations, estimates thick-target neutron yields for incident electron energies Eo above 50 MeV. Giant dipole resonance neutron yields, calculated by several analytic formulas for the differential photon track length, are compared with EGS4 calculations. Modifications to the analytic formulas are suggested. A scaling function is derived to estimate, from the thick-target formula, neutron yields produced in thin targets.

Characterization of Bangor virus proteins by using monoclonal antibodies

A new virus was isolated from a finch in quarantine in Northern Ireland in 1973. The virus had the morphological characteristics of a paramyxovirus, and was named Bangor virus (BaV). In order to identify the structural proteins of BaV and to investigate the biological characterization of the virus, 28 monoclonal antibodies (mAbs) directed against BaV were prepared. Eight of these mAbs reacted with the nucleocapsid protein (NP), 10 with hemagglutinin-neuraminidase (HN) protein, and 10 with fusion (F) protein. With the aid of these mAbs, the structural proteins of BaV were determined, namely, p52, gp74, gp63, and gp51 were identified as the NP, HN, F0, and F1 proteins, respectively. The biological activities of the mAbs directed against the envelope glycoproteins of BaV were examined. Intriguingly, it was found in the neutralization assay that four mAbs directed against the HN protein of BaV can enhance the fusion of HeLa cells infected with BaV, showing the presence of a potential third function of the HN protein that affects the fusion activity of the F protein. Furthermore, all of the anti-F protein mAbs showed neutralizing activity.

Yeast mRNA cap methyltransferase is a 50-kilodalton protein encoded by an essential gene

RNA (guanine-7-)methyltransferase, the enzyme responsible for methylating the 5' cap structure of eukaryotic mRNA, was isolated from extracts of Saccharomyces cerevisiae. The yeast enzyme catalyzed methyl group transfer from S-adenosyl-L-methionine to the guanosine base of capped, unmethylated poly(A). Cap methylation was stimulated by low concentrations of salt and was inhibited by S-adenosyl-L-homocysteine, a presumptive product of the reaction, but not by S-adenosyl-D-homocysteine. The methyltransferase sedimented in a glycerol gradient as a single discrete component of 3.2S. A likely candidate for the gene encoding yeast cap methyltransferase was singled out on phylogenetic grounds. The ABD1 gene, located on yeast chromosome II, encodes a 436-amino-acid (50-kDa) polypeptide that displays regional similarity to the catalytic domain of the vaccinia virus cap methyltransferase. That the ABD1 gene product is indeed RNA (guanine-7-)methyltransferase was established by expressing the ABD1 protein in bacteria, purifying the protein to homogeneity, and characterizing the cap methyltransferase activity intrinsic to recombinant ABD1. The physical and biochemical properties of recombinant ABD1 methyltransferase were indistinguishable from those of the cap methyltransferase isolated and partially purified from whole-cell yeast extracts. Our finding that the ABD1 gene is required for yeast growth provides the first genetic evidence that a cap methyltransferase (and, by inference, the cap methyl group) plays an essential role in cellular function in vivo.

The D1 and D12 subunits are both essential for the transcription termination factor activity of vaccinia virus capping enzyme

Transcription termination by vaccinia virus RNA polymerase during synthesis of early mRNAs requires a virus-encoded termination factor (VTF). VTF is but one of many activities associated with the vaccinia virus mRNA capping enzyme, a heterodimer of 95- and 33-kDa subunits encoded by the D1 and D12 genes, respectively. Although the three catalytic domains involved in cap formation have been assigned to individual subunits or portions thereof, the structural requirements for VTF activity are unknown. We now report that both full-length subunits are required for transcription termination. The 844-amino acid D1 subunit by itself, which is fully active in triphosphatase and guanylyltransferase functions, has no demonstrable VTF activity in vitro. Neither does the D12 subunit by itself. The heterodimeric methyltransferase domain of D1 (residues 498 to 844) and D12 subunits also has no VTF activity. VTF is not affected by a K-to-M mutation of the guanylyltransferase active site at position 260 (K260M) that abolishes enzyme-GMP complex formation or by a H682A/Y683A double mutation of the D1 subunit, which abrogates methyltransferase activity. Thus, the structural requirements for termination are distinct from those for nucleotidyl transfer and methyl transfer.

Structural and functional analyses of the transcription-translation proteins NusB and NusE

The NusB and NusE (ribosomal protein S10) proteins function in transcription and translation. The two proteins form a complex that binds to the boxA sequence found in the leader RNA of rrn operons; boxA is required for transcription antitermination in rrn operons. Although binding of these two proteins to the boxA RNA of the bacteriophage lambda nut site has not been observed, both NusB and NusE as well as the RNA boxA sequence are required for lambda N-mediated antitermination. Studies identifying the amino acid changes caused by mutations in nusB and nusE and relating these changes to altered function are reported. It is concluded that boxA is essential for an effective NusB contribution to N-mediated antitermination and that by mutation NusB may be changed to allow more-effective binding to boxA variants.

CCAAT-box contributions to human thymidine kinase mRNA expression

In order to examine the role of two inverted CCAAT boxes near the start of transcription of the human thymidine kinase (TK) gene, a series of constructs were prepared in which one or both CCAAT boxes were deleted or mutated. These altered promoters (1.2 kb of 5'-flanking sequence) were used to express a TK minigene containing the first two exons and introns followed by the remainder of the cDNA. RNA blots were prepared from stable cell lines of ts13 cells containing these constructs under three conditions: 1) serum deprived cells, 2) serum stimulated cells, and 3) cells that had been stimulated with serum, but were arrested in the G1 phase of the cell cycle by the temperature sensitive mutation carried by these cells. TK mRNA expression from each construct was suppressed by the temperature sensitive block to cell cycle progression. Measurement of protein expression from the various altered TK promoters indicated that both CCAAT boxes contribute to promoter strength. These experiments also suggested that the two CCAAT boxes were not equivalent and that the distal CCAAT could substitute for the proximal CCAAT, but the converse was not true.

Protein that binds to the distal, but not to the proximal, CCAAT of the human thymidine kinase gene promoter

Mobility shift assays were used to examine protein binding to the human TK gene CCAAT boxes. Similar protein binding patterns were observed with probes containing either the proximal or distal CCAAT. However, probes containing both CCAAT boxes in which one of the CCAAT boxes was inactivated by mutation did not demonstrate identical binding patterns. One of the complexes formed with the longer probes was only observed when the distal CCAAT was intact. This species was not formed with probes that only contained an intact proximal CCAAT, and its formation could only be competed by oligonucleotides containing the distal CCAAT motif. This observation reveals the existence of a protein that can bind to the distal, but not to the proximal, CCAAT of the human TK promoter. This protein may account for the previous observation that the two CCAAT motifs are not functionally equivalent. The protein that binds to the distal, but not to the proximal, CCAAT (DTK-CBP) was also present in two human cell lines. Significantly more DTK-CBP was present in nuclear extracts of HepG2 and WI38 cells than in TK-ts13 cells. However, this protein was not observed in three different murine cell lines and one primary culture. Its abundance in some human cell lines suggests it might modulate the expression of human TK mRNA in cells that express this protein.

Solution structure of the ets domain of Fli-1 when bound to DNA

Members of the ets family of transcription factors share a conserved DNA-binding domain, the ets domain. By using multidimensional NMR, we have determined the structure of the ets domain of human Fli-1 in the DNA-bound form. It consists of three alpha-helices and a four-stranded beta-sheet, similar to structures of the class of helix-turn-helix DNA binding proteins first found in the catabolite activator protein of Escherichia coli. NMR and mutagenesis experiments suggest that in comparison to structurally related proteins, the ets domain uses a new variation of the helix-turn-helix motif for binding to DNA.

Mutational analysis defines a C-terminal tail domain of RAP1 essential for Telomeric silencing in Saccharomyces cerevisiae

Alleles specifically defective in telomeric silencing were generated by in vitro mutagenesis of the yeast RAP1 gene. The most severe phenotypes occur with three mutations in the C-terminal 28 amino acids. Two of the alleles are nonsense mutations resulting in truncated repressor/activator protein 1 (RAP1) species lacking the C-terminal 25-28 amino acids; the third allele is a missense mutation within this region. These alleles define a novel 28-amino acid region, termed the C-terminal tail domain, that is essential for telomeric and HML silencing. Using site-directed mutagenesis, an 8-amino acid region (amino acids 818-825) that is essential for telomeric silencing has been localized within this domain. Further characterization of these alleles has indicated that the C-terminal tail domain also plays a role in telomere size control. The function of the C-terminal tail in telomere maintenance is not mediated through the RAP1 interacting factor RIF1: rap1 alleles defective in both the C-terminal tail and RIF1 interaction domains have additive effects on telomere length. Overproduction of SIR3, a dose-dependent enhancer of telomeric silencing, suppresses the telomeric silencing, but not length, phenotypes of a subset of C-terminal tail alleles. In contrast, an allele that truncates the terminal 28 amino acids of RAP1 is refractory to SIR3 overproduction. These results indicate that the C-terminal tail domain is required for SIR3-dependent enhancement of telomeric silencing. These data also suggest a distinct set of C-terminal requirements for telomere size control and telomeric silencing.

The secondary structure of the ets domain of human Fli-1 resembles that of the helix-turn-helix DNA-binding motif of the Escherichia coli catabolite gene activator protein

The ets family of eukaryotic transcription factors is characterized by a conserved DNA-binding domain of approximately 85 amino acids for which the three-dimensional structure is not known. By using multidimensional NMR spectroscopy, we have determined the secondary structure of the ets domain of one member of this gene family, human Fli-1, both in the free form and in a complex with a 16-bp cognate DNA site. The secondary structure of the Fli-1 ets domain consists of three alpha-helices and a short four-stranded antiparallel beta-sheet. This secondary structure arrangement resembles that of the DNA-binding domain of the catabolite gene activator protein of Escherichia coli, as well as those of several eukaryotic DNA-binding proteins including histone H5, HNF-3/fork head, and the heat shock transcription factor. Differences in chemical shifts of backbone resonances and amide exchange rates between the DNA-bound and free forms of the Fli-1 ets domain suggest that the third helix is the DNA recognition helix, as in the catabolite gene activator protein and other structurally related proteins. These results suggest that the ets domain is structurally similar to the catabolite gene activator protein family of helix-turn-helix DNA-binding proteins.