[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.