HIV-1 infection in commercial plasma donors in China.
Explore the source record for details and available documents.
Adolescent↗
Biomedical subjects
Z Liu
Publications and source records attributed to Z Liu.
Gene disruption of a G4-DNA-dependent nuclease in yeast leads to cellular senescence and telomere shortening.
The yeast gene KEM1 (also named SEP1/DST2/XRN1/RAR5) produces a G4-DNA-dependent nuclease that binds to G4 tetraplex DNA structure and cuts in a single-stranded region 5' to the G4 structure. G4-DNA generated from yeast telomeric oligonucleotides competitively inhibits the cleavage reaction, suggesting that this enzyme may interact with yeast telomeres in vivo. Homozygous deletions of the KEM1 gene in yeast block meiosis at the pachytene stage, which is consistent with the hypothesis that G4 tetraplex DNA may be involved in homologous chromosome pairing during meiosis. We conjectured that the mitotic defects of kem1/sep1 mutant cells, such as a higher chromosome loss rate, are also due to failure in processing G4-DNA, especially at telomeres. Here we report two phenotypes associated with a kem1-null allele, cellular senescence and telomere shortening, that provide genetic evidence that G4 tetraplex DNA may play a role in telomere functioning. In addition, our results reveal that chromosome ends in the same cells behave differently in a fashion dependent on the KEM1 gene product.
Blotting, Southern↗
Functional synergism in the carbohydrate-induced activation of liver-type pyruvate kinase gene expression.
Hepatic expression of the liver-type pyruvate kinase (L-PK) gene is induced at the transcriptional level by increased carbohydrate metabolism in the rat. The carbohydrate response of the L-PK gene requires sequences from -171 to -124, which encompass adjacent major late transcription factor (MLTF)-like and hepatic nuclear factor (HNF)-4 binding sites. Neither site alone is capable of conferring a response, prompting us to explore the mechanism of synergy between the MLTF-like factor and HNF-4. Spacing requirements between the two factor binding sites were tested by generating a series of mutations that altered the distance between these sites. Surprisingly, all of the constructs with spacing mutations were capable of responding to elevated glucose when introduced into primary hepatocytes. Thus the glucose response does not depend on the rigid phasing of the MLTF-like and HNF-4 factors, suggesting that the factors binding to these two sites do not interact directly with each other. Substitution or inversion of the PK HNF-4 site abrogated the response to glucose and also significantly suppressed the promoter activity under non-inducing conditions. We conclude that the MLTF-like factor and HNF-4 co-operate functionally to maintain the basal activity, as well as the carbohydrate responsiveness, of the L-PK gene. A mechanism other than co-operative DNA binding is responsible for the synergism.
Animals↗
Cellubrevin is a resident protein of insulin-sensitive GLUT4 glucose transporter vesicles in 3T3-L1 adipocytes.
Insulin stimulates glucose transport in muscle and fat cells by inducing translocation of GLUT4 glucose transporters from a storage site to the cell surface. The mechanism of this translocation and the identity of the storage site are unknown, but it has been hypothesized that transporters recycle between an insulin-sensitive pool, endosomes, and the cell surface. Upon cell homogenization and fractionation, the storage site migrates with light microsomes (LDM) separate from the plasma membrane fraction (PM). Cellubrevin is a recently identified endosomal protein that may be involved in the reexocytosis of recycling endosomes. Here we describe that cellubrevin is expressed in 3T3-L1 adipocytes and is more abundant in the LDM than in the PM. Cellubrevin was markedly induced during differentiation of 3T3-L1 fibroblasts into adipocytes, in parallel with GLUT4, and the development of insulin regulated traffic. In response to insulin, the cellubrevin content decreased in the LDM and increased in the PM, suggesting translocation akin to that of the GLUT4 glucose transporter. Vesicle-associated membrane protein 2 (VAMP-2)/synaptobrevin-II, a protein associated with regulated exocytosis in secretory cells, also redistributed in response to insulin. Both cellubrevin and VAMP-2 were susceptible to cleavage by tetanus toxin. Immunopurified GLUT4-containing vesicles contained cellubrevin and VAMP-2, and immunopurified cellubrevin-containing vesicles contained GLUT4 protein, but undiscernible amounts of VAMP-2. These observations suggest that cellubrevin and VAMP-2 are constituents of the insulin-regulated pathway of membrane traffic. These results are the first demonstration that cellubrevin is present in a regulated intracellular compartment. We hypothesize that cellubrevin and VAMP-2 may be present in different subsets of GLUT4-containing vesicles.
3T3 Cells↗
Detection of a novel transcription factor for the A alpha fibrinogen gene in response to interleukin-6.
The three fibrinogen genes belong to the class II hepatic acute phase proteins that are regulated in part by members of the interleukin-6 (IL-6) family of cytokines and glucocorticoids. The common DNA sequence that characterizes this group of proteins is a hexanucleotide CTGGGA residing in the promoter regions of these genes. Investigations of IL-6 control of the A alpha fibrinogen gene by electrophoretic mobility shift assays using a 30-base pair DNA probe containing the CTGGGA element revealed that a novel protein is associated with this site during non-IL-6-stimulated conditions. Sensitive time-course studies of IL-6 stimulation using primary hepatocyte cultures, high resolution polyacrylamide gel electrophoresis, and site-directed mutagenesis show that upon IL-6 stimulation of hepatocytes, this DNA binding protein transiently leaves the CTGGGA site and binds 12 base pairs down-stream but then begins to re-associate with the original DNA site at 1 h and is completed by 2 h. A recently characterized and cloned IL-6-activated transcription factor, Stat-3, which has been reported to bind a CT-GGGAA site in the alpha-2 macroglobulin gene, another member of the class II acute phase proteins, does not bind to the CTGGGA sequence in the A alpha fibrinogen gene. These findings reveal the presence of a previously undefined IL-6-regulated event, which involves a new DNA binding protein and demonstrates for the first time additional details of the kinetics of IL-6 control of fibrinogen gene expression.
Animals↗
Study of the abzyme with peroxidase catalytic activity.
Explore the source record for details and available documents.
Animals↗
A new strategy for generating selenium-containing abzyme. Chemical mutation of monoclonal antibodies with substrate-binding sites.
Explore the source record for details and available documents.
Animals↗
GABAA receptor beta 1, beta 2, and beta 3 subunits: comparisons in DBA/2J and C57BL/6J mice.
GABAA receptors link binding of GABA (gamma-aminobutyric acid) to inhibitory chloride flux in the brain. They are the site of action of several important classes of drugs, and have been implicated in animal models of epilepsy and in the actions of alcohol. We compare the sequence and expression of the beta 1, beta 2 and beta 3 subunits of GABAA receptors in two inbred strains of mice, DBA/2J and C57BL/6J, which differ markedly in seizure susceptibility and in a variety of behaviors related to alcohol. Only the beta 3 subunit had strain differences in cDNA nucleotide sequence, which did not affect amino acid sequence but which did create restriction fragment length polymorphisms (RFLPs) potentially useful in gene mapping. We have also tested mouse beta 1 and beta 2 subunits for internal alternative splicing, detecting none.
Alcohol Drinking↗
The expression levels of the human papillomavirus type 16 E7 correlate with its transforming potential.
The transforming potential of the human papillomavirus (HPV) type 16 has been defined largely in the E7, E6, and E5 oncoproteins, with the major transforming capability residing in the E7 gene. In this paper, we found that in cooperation with the activated ras, the HPV16 E7 gene when expressed in a retroviral vector could fully transform baby rat kidney (BRK) cells in transfections, whereas the same construct could only immortalize the BRK cells following retroviral infection. This inability to transform correlated with the low levels of E7 gene RNA expression in the viral infected cells, which harbor a lower number of copies of the E7 gene constructs. Cotransfection of the expression vector FV2E7, which gives high levels of E7 gene expression, and activated ras lead to rapid and efficient morphological transformation of BRK cells which grew easily in soft agar and induced large tumors in athymic nude mice. In contrast, cotransfections of the expression vector FV1E7, which gives lower levels of E7 gene expression, produced much lower numbers of transformed colonies which took longer to form, showed a retarded growth on soft agar, and induced smaller tumors in nude mice. Under these conditions, colonies of immortalized, but morphologically untransformed cells formed in large numbers. These results indicate that the transforming potential is directly correlated to the expression levels of the oncoprotein and that a threshold level of the E7 oncoprotein may be required before the cells can be fully transformed. This supports the hypothesis that the transformation processes include at least two separate and continuous steps which first lead to immortalization and then to metastasis, in agreement with the clinical progression of genital tumors from benign to malignancy. Such a progression may involve enhanced expression of the oncoproteins.
Animals↗
Loop-expansion study of the single-hole spectral function in the t-J model.
Explore the source record for details and available documents.
Journal Article↗
Use of site-directed mutagenesis to identify the galactosyltransferase binding sites for UDP-galactose.
Site-directed mutagenesis was utilized to identify binding sites for UDP-galactose in galactosyltransferase (EC 2.4.1.22). Mutant cDNAs were generated by a procedure based on PCR, and the mutated enzymes were expressed in E.coli cells. The mutant enzymes were purified by Ni-NTA Sephadex, and the degree of purification was judged by SDS-PAGE. Purified mutant GTs, F305L, P306V, N307S, N308S, showed dramatic decreases in activities in comparison with the activity of the wild-type GT. Enzyme kinetic analysis revealed that the Km values of F305L, P306V, N307S and N308S for UDP-galactose were, respectively, 9-, 11-, 50- and 20-fold higher than the Km of wild-type GT, but the Km values for manganese were not significantly different from that of the wild-type GT. The quartet mutant F305L/P306V/N307S/N308S showed no activity. From the results of this study it is concluded that amino acids, Phe-305, Pro-306, Asn-307 and Asn-308, in GT are most probably involved in GT catalysis or are located close to the UDP-galactose binding region but are not involved in the binding of manganese.
Amino Acid Sequence↗
Work performance of Chinese cycle haulers: controlled field experiments in normal work conditions.
Forty-five male Chinese cycle haulers performed a controlled field experiment under mild winter conditions. The objective was to gain insight into factors that affect work performance. Each man hauled the same 481-kg load around a Beijing street course of 14.18 km. The experiment was a measured sample of the same work they do routinely, on the same roads, using similar human powered hauling cycles (modified only enough to carry observers and instruments). The course was completed at a mean speed of 10.4 kph and mean time of 84.2 min. While there was considerable variation in individual pace and in pace change during work, the haulers performed at relatively high output in reference to their capacities. Mean heart rate was 156.8 +/- 16.1 bpm, 83.9% of maximum. The men had average body build and were average in size for the general Chinese population (X stature = 169.7 cm) although they showed relatively high aerobic capacity (determined in laboratory tests). Performance levels during experiments appear to match habitual work patterns, and self-pacing emerged as a major behavioral finding of this research. Speed, a primary index of job performance, showed significant correlation to heart rate, VO2max, variation in windchill, self-reported health and other variables, with a multiple regression coefficient of 0.811. Similar patterns were seen for heart rate relative to speed, except that physical size, education, and other behavioral variables were also predictors.
Adult↗
Germline mutations in the RB1 gene in patients with hereditary retinoblastoma.
We have analyzed the 27 exons and the promoter region of the RB1 gene in familial or sporadic bilateral retinoblastoma by using single-strand conformation polymorphism analysis. For improvement over previous studies, a new set of primers has been designed, which allow for amplification of the coding and splicing sequences only. The positioning of the polymerase chain reaction (PCR) primers was such that the resulting PCR products were of different sizes, which enabled us to analyze two different exons simultaneously and still distinguish between the banding profiles for both (biplex analysis). By using this approach, we were able to identify mutation in 22 new patients, but the overall efficiency of the procedure when we used a single-pass regimen was only 48%. The mutations were small insertions and deletions and point mutations in roughly equal proportions.
Base Sequence↗
A fast, reliable, automatic shimming procedure using 1H chemical-shift-imaging spectroscopy.
The importance and the difficulty of achieving good B0 homogeneity over the volume of interest in in vivo NMR spectroscopy are well known. A fast, reliable, versatile, and fully automatic shimming procedure has been developed, using 3D chemical-shift imaging to measure the field distribution using only the water peak in the sample of interest. The procedure minimizes the mean-square error in the field distribution with respect to a constant field where the signal exists (e.g., the head). This produces a set of linear equations that can be solved by standard matrix methods. The procedure has been applied on a commercial imager producing water linewidths from the entire head as low as 8 Hz at 1.5 T. The mean linewidth and standard deviation from 94 head studies were 11.7 +/- 1.9 Hz.
Algorithms↗
Weanling female Sprague-Dawley rats are not sensitive to the antiestrogenic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).
Investigators have shown that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can inhibit certain estrogenic events in vivo and in vitro. To further investigate this phenomenon, the effects of estradiol (E2) alone or TCDD plus estradiol on several estrogen-dependent parameters were evaluated in weanling female Sprague-Dawley rats. E2 (10 micrograms/kg/day, Postnatal Days (PND) 21 and 22) caused significant increases in relative uterine weight and keratinization of the vaginal epithelium (PND 23). E2 significantly reduced uterine estrogen receptor (ER) protein levels and serum FSH levels, with a trend toward reduction of ER mRNA levels. None of these parameters were affected by pretreatment with 20, 40, or 80 micrograms/kg TCDD (PND 19). Uterine progesterone receptor levels were not affected by E2 or TCDD in the present study. In contrast, TCDD significantly decreased body weight (40 or 80 micrograms/kg) by PND 21, significantly decreased relative thymic weights, and significantly increased relative hepatic weights (20, 40, and 80 micrograms/kg, by PND 23). In addition, TCDD dramatically induced CYPIA1 hepatic mRNA levels, indicating that TCDD was properly delivered and could mediate other well-documented Ah receptor-dependent events. Thus, weanling female Sprague-Dawley rats are not sensitive to the antiestrogenic effects of TCDD at doses which cause overt toxicity. The results provide evidence that the previously reported antiestrogenic effects of TCDD are probably species, strain, and age dependent.
Animals↗
Studies of diagnosis and pathogenesis of Wilson's disease.
We have studied the copper and metallothionein (MT) in culture skin fibroblasts of patients and heterozygotes with Wilson's disease (WD) and controls (5 cases each) after incubation in mediums containing various concentrations of copper (C1: 15.74 mumol/L, C2: 78.70 mumol/L, C3: 157.38 mumol/L, C4: 314.76 mumol/L). The results are as follows: 1. In each of the three groups, the copper/protein ratio (Cu/P) in cytosols of 1-5 passages is significantly higher than that of 6-10, 11-15, 16-20 passages. There are no significant differences among 6-10, 11-15 and 16-20 passages. 2. In standard medium, Cu/P in cytosols of three groups are not significantly different, but Cu/P of patients is significantly higher than that of the other two groups after incubation in C4 medium for 12 or 24 hours. 3. After incubation in C1, C2, C3 and C4 mediums respectively, the Cu/P in cytosols of the three groups only increased in C4 medium with time (within 72 hours). It is higher in the patient group than the other two groups. 4. In the three groups, cytosol copper distributed similarly in two peaks after Sephadex G-75 chromatography, which are on high molecular weight (HMW) proteins and MT fractions respectively. It remained the same after incubation in various concentrations of copper. The copper content found in MT fractions in WD patients is much higher than that of controls and heterozygotes. It is even higher after incubation in various concentrations of copper but no changes was found in controls and heterozygotes.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
The location of untranscribed DNA sequences within ras genes essential for eliciting plant growth suppression.
Three heterologous ras DNA-coding sequences and their deletion derivatives were introduced into plant cells to investigate the role of the ras-coding sequences, especially conserved regions, in eliciting growth inhibition. All three ras-coding sequences caused a similar inhibition of plant cell growth, and it was the conserved coding regions which were responsible for this inhibitory effect. The 493 bp conserved region within the v-Ha-ras-coding sequence was studied further, and was shown to be responsible for the inhibitory effect. This region is conserved (over 44%) among the three ras genes studied and encodes a catalytic region of the Ras protein. Small deletions at either the 5' or 3' end of this 493 bp sequence could abolish or dramatically reduce the inhibitory effect. A 36 bp region at the 5' end of the 493 bp region was found to be highly conserved between v-Ha-ras and eight different plant ras or ras-related genes based upon analysis of published sequences. Small deletions affecting this highly conserved 36 bp region completely abolished the inhibitory effect, while deletion of a similar number of base pairs in adjacent regions did not. These results indicate that plant growth inhibition by ras DNA requires small regions at both ends of the 493 bp conserved region.
Base Sequence↗
Specific binding of avidin to biotin containing lipid lamella surfaces studied with monolayers and liposomes.
The interaction of avidin (from egg white) with phospholipid (monolayer and bilayer) model membranes containing biotin-conjugated phospholipids has been studied. In the first part, using surface sensitive techniques (ellipsometry and surface plasmon resonance) we demonstrated that the nonspecific adsorption of avidin to phospholipid lamella could be abolished by adding an amount of Ca2+, Mg2+ or Ba2+ that led to an electrostatic interaction. The specific binding of avidin to lipid mixtures containing biotin-conjugated phospholipids was obviously composition dependent. The ratio 1:12 of a B-DPPE/DPPE mixture was found to be the optimum molar ratio. When we compared the results from the surface sensitive techniques with those from the electron micrographs of a two dimensional crystal of avidin (obtained in our laboratory), the optimum ratio was found to be determined by the effect of lateral steric hindrance. In the second part, we observed the pattern of the layers of fluorescently labeled phospholipid and adsorbed proteins with a home-made micro fluorescence film balance. The fluorescence images showed that avidin was preferentially bound to the receptors that were in the fluid domains. Further, with a sensitive fluorescence assay method, the effect of the phase behavior of liposomes on the specific binding of avidin was measured. This showed that avidin interacted with biotinlipid more weakly in the gel state liposome than in the liquid state liposome. The major conclusion was that the binding of avidin to a membrane bound model receptor was significantly restricted by two factors: one was the lateral steric hindrance and the other was the fluidity of the model membrane.
Adsorption↗