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Biomedical subjects

B Feng

Publications and source records attributed to B Feng.

At least 91 records · Page 5Linked to original sources
PubMed1995

Solution structure of an oligodeoxynucleotide containing the human n-ras codon 61 sequence refined from 1H NMR using molecular dynamics restrained by nuclear Overhauser effects.

The solution structure of the ras61 oligodeoxynucleotide duplex d(CGGACAAGAAG). d(CTTCTTGTCCG), which consists of codons 60, 61 (underlined), and 62 of the human n-ras protooncogene, was refined from 1H NMR data. The sequence contains a run of purines in the coding strand, with one R-Y step, A4.T19-->C5.G18, and one Y-R step, C5.G18-->A6.T17 (excluding the 5'-terminal base pair). The NMR data were consistent with a B-like helix as judged by characteristic internucleotide NOEs. The NOE intensities between purine H8 and purine anomeric protons were small as compared to the intensities between cytosine H5 and H6 protons, indicative of glycosyl torsion angles in the anti range. Cross-peaks were observed between purine H8 and pyrimidine H5 and CH3 protons on adjacent bases in the direction of purine (5'-->3') pyrimidine, but not in the direction pyrimidine (5'-->3') purine. Watson-Crick hydrogen bonding was intact and enabled the assignment of the exchangeable protons. A total of 226 experimental distance restraints were obtained. A restrained molecular dynamics and simulated annealing approach was utilized in the refinement. The data for 5 emergent molecular dynamics (MD) structures calculated from a B-form starting structure and 5 emergent MD structures calculated from an A-form starting structure refined to an average pairwise root-mean-square (rms) difference of 1.2 A, with maximum pairwise rmsd of 1.7 A. The accuracy of the emergent structures was assessed by complete relaxation matrix back-calculation. The sixth root residual index of 9.4 x 10(-2) was measured between the refined structures and the NOE data, suggesting that the former were in reasonable agreement with the data. The refined structures revealed an increased roll angle of 7 degrees in the codon 61 sequence at base step C5.G18-->A6.T17, which relieved the purine-purine clash in the minor groove, and in turn relieved the purine-purine clash in major groove between A4.T19 and C5.G18. A 3.7 A rise between C5.G18 and A6.T17 was calculated, which assisted in relieving the purine-purine clash. The local variations in the B-like conformation did not confer large structural alterations upon the ras61 sequence, but could be important in modulating the reactivity of the first as compared to the second adenine in codon 61.

Base Composition↗
PubMed1995

Sequence-specific DNA binding by NIT4, the pathway-specific regulatory protein that mediates nitrate induction in Neurospora.

The expression of the structural genes nit-3 and nit-6, which encode the nitrate assimilatory enzymes nitrate reductase and nitrite reductase, respectively, is highly regulated by the global-acting NIT2 regulatory protein. These structural genes are also controlled by nitrogen catabolite repression and by specific induction via nitrate. A pathway-specific regulatory protein, NIT4, appears to mediate nitrate induction of nit-3 and of nit-6. The NIT4 protein, composed of 1090 amino acids, contains a putative GAL4-like Cys-6 zinc cluster DNA-binding motif, which is joined by a short segment to a stretch of amino acids that appear to constitute a coiled-coil dimerization domain. Chemical crosslinking studies demonstrated that a truncated form of NIT4 forms homodimers. Mobility-shift and DNA-footprinting experiments have identified two NIT4-binding sites of significantly different strengths in the promoter region of the nit-3 gene. The stronger binding site contains a symmetrical octameric sequence, TCCGCGGA, whereas the weaker site has a related sequence. Sequences related to this palindromic element can be found upstream of the nit-6 gene.

Amino Acid Sequence↗
PubMed1995

Does the common bile duct dilate after cholecystectomy? Sonographic evaluation in 234 patients.

OBJECTIVE: The purpose of this study was to determine whether the common bile duct dilates after cholecystectomy. SUBJECTS AND METHODS: All 234 patients who had cholecystectomy at our hospital between October 1985 and April 1994 were included in this study. The luminal diameter of the proximal segment of the common bile duct was measured on antero-posterior transverse sonograms 4-15 days before cholecystectomy. In all patients, the luminal diameter was measured again on sonograms obtained 7-2160 days after surgery (mean, 393 days; median, 180 days; mode, 360 days). A diameter of 6 mm or less was considered normal. This study contained 197 patients with a normal common bile duct (< or = 6 mm) and 37 patients with a dilated common bile duct (> 6 mm). RESULTS: The mean diameter of the common bile duct measured on sonograms was 5.9 mm before cholecystectomy and 6.1 mm after cholecystectomy. This difference was statistically significant (p < .05). The diameter of the common bile duct increased in 110 patients, decreased in 61 patients, and stayed the same in 63 patients. Of the 234 patients, 197 (84%) had a normal preoperative diameter of the common bile duct, whereas 167 (71%) had a common bile duct with a normal diameter postoperatively. CONCLUSION: The diameters of the common bile duct as measured on sonograms increase slightly after cholecystectomy. Most patients do not have significant compensatory dilatation of the duct after cholecystectomy.

Adult↗
PubMed1995

[Study on the calibration model of electronystagmography (ENG) in the guinea pigs].

The passive calibration of ENG according to the gain of OKN evoked in guinea pigs was studied in this paper. The method was also verified by animal experiment and the comparison between active calibration and passive one in normal subjects. OKN was elicited by optokinetic drum with black and white strips at 10 intervals at velocity of 5-60 degrees/s. The calculating formula of passive calibration in animals obtained by mathematical corollary is K = G . ST sigma . DV/SA sigma. The slow-phase velocity of spontaneous nystagmus in a group of animals with acute loss of unilateral vestibular function recorded with this method showed typically a logarithmic decline within 24 hours. No significant difference between the values of active and passive calibration was found in normal subjects. The results demonstrated that the method described in the paper was accurate and reliable. It can be used in perivestibular experiments.

Animals↗
PubMed1995

[Preparation and characterization of liposomal adriamycin].

We established a more suitable methodology for preparing liposomal adriamycin (Lipo-ADM) by a remote loading technique. This procedure is convenient, simple with an entrapment efficiency of 95%. The mean diameter of liposome is about 100nm showing unilamellar spherical shape. The leakage ratio is about 10% within 24hr. Those characteristics fit for clinical demand.

Doxorubicin↗
PubMed1994

The production of strains highly expressing human interleukin-2 cDNA.

The plasmid pTLIL-2, which only directed a low-level expression of human interleukin 2(IL-2) cDNA in E. coli, was reconstructed: a series of deletions were made in 3' non-coding region of human IL-2 cDNA, and 7 recombinant plasmids with different deletions were selected, on the other hand, a Tac promoter sequence from pDR540 was inserted to upstream of IL-2 cDNA in pTLIL-2 so that pTLIL-2DT, which contains double Tac promoters, was constructed. And then, E. coli JM103 was transformed with the above 8 recombinant plasmids respectively. The expression efficiency of IL-2 cDNA in E. coli transformed with different plasmids was evaluated by means of SDS-PAGE and measuring 3H-TdR incorporation of IL-2-dependent activated T lymphocytes in the presence of bacterial extracts. Three engineering strains with high efficiency of IL-2 expression were selected, and all of these strains could produce recombinant IL-2(rIL-2) 4 times more than E. coil JM103/pTLIL-2.

DNA Transposable Elements↗
PubMed1994

A reporter gene analysis of penicillin biosynthesis gene expression in Penicillium chrysogenum and its regulation by nitrogen and glucose catabolite repression.

Vectors which possess a truncated niaD gene encoding nitrate reductase were developed to allow targeted gene integration during transformation of an niaD mutant Penicillium chrysogenum host. The Penicillium genes pcbC and penAB are immediately adjacent to each other and are divergently transcribed, with an intergenic control region serving as their promoters. Gene fusions were constructed with a reporter gene, uidA, which encodes beta-glucuronidase. The pcbC-penAB intergenic region was fused to the uidA gene in both orientations so that regulated expression of each structural gene could be investigated. These fusion genes were targeted to the chromosomal site of the niaD locus of P. chrysogenum, and their expression was examined under different growth conditions. The expression of each of these penicillin biosynthesis genes was found to be regulated by nitrogen repression, glucose repression, and growth stage control.

Base Sequence↗
PubMed1994

Effects of vitamins and methionine on blastogenic response of splenocytes and lipid peroxidation in lung and liver of mice exposed to SiO2 dust.

We studied the effects of nutrients such as vitamin C, E, B6, niacin, and methionine on the blastogenic response of splenocytes and lipid peroxidation (LPO) in lung and liver of mice exposed to SiO2 dust. The results showed that after treatment with SiO2, the blastogenic response of splenocytes decreased significantly (p < 0.001), whereas the LPO level in lung and liver increased remarkably (lung p < 0.05; liver p < 0.001). Vitamin E, C, and niacin strongly enhanced the blastogenic response of T and B splenic lymphocytes to concanavalin-A and to lipopolysaccharide (p < 0.001). The effects of methionine and B6 were much less intense. Other supplied nutrients have been shown to inhibit LPO in lung and liver of mice exposed to SiO2 (p < 0.001).

Animals↗
PubMed1993

Recognition of specific nucleotide bases and cooperative DNA binding by the trans-acting nitrogen regulatory protein NIT2 of Neurospora crassa.

The NIT2 nitrogen regulatory protein of Neurospora is a DNA binding protein which contains a single Cys2/Cys2 type finger motif followed immediately by a highly basic region. Several different approaches were employed to identify nucleotides which appear to be in contact with NIT2 in the DNA-protein complex. Methylation interference and missing contact analyses with the promoter DNA fragment of the L-amino acid oxidase gene showed that all three purines in both of two GATA core sequences and the single adenine residue in each of the complementary TATC sequences were in intimate contact with NIT2. Modification or loss of the three purine residues located between the two GATA core sequences also significantly reduced NIT2 binding, whereas alteration of purines which flank the binding element showed only minor effects. Chemical modification of all six thymine bases in the two GATA and TATC complement core sequences also strongly affected NIT2 binding. High affinity NIT2 binding sites appear to contain at least two GATA core sequences, with single GATA sequences acting only as weak binding sites. Mobility shift experiments with the DNA fragment upstream of nit-3, the structural gene for nitrate reductase, revealed two DNA-NIT2 protein complexes. In complex I, which is formed first, NIT2 was bound to a pair of GATA sites located at -180. In complex II, the paired GATA sites at -180 plus a single GATA site at -290 were all occupied by NIT2. A DNA fragment containing only the single -290 GATA element bound NIT2 very weakly. The affinity of this single GATA for NIT2 was ten to twenty times greater when it was situated on the same DNA fragment with the distant paired GATA elements than when alone.

Amino Acid Sequence↗
PubMed1993

Effects of GAL10-SUC2 promoter combinations on SUC2 gene expression in S. cerevisiae.

The plasmid series YEP51 delta n bearing GAL10-SUC2 promoter combinations were constructed by inserting SUC2 gene with different upstream deletions downstream GAL10 promoter on YEP51. After transforming yeast cells S. cerevisiae, the invertases expressed by each of the transformants were measured and analysed by means of PAGE. The results showed that: 1) The SUC2 gene with upstream deletion to at -636bp expressed high level glycosylated form of invertase under glucose derepression, while SUC2 gene with more extensive deletions to -223 bp or more lost its response to glucose derepression; 2) Each part of GAL10-SUC2 promoter combination acted almost independently. All of the combinations showed no apparent coordinated promoter function under our experimental conditions; 3) Sequences between -89bp and -41bp of SUC2 upstream region are responsible for constitutive expression of nonglycosylated invertase. The two tracts of poly (dA-dT) of this region may serve as promoter elements.

DNA Transposable Elements↗
PubMed1993

Tissue inhibitor of metalloproteinases (TIMP, aka EPA): structure, control of expression and biological functions.

The TIMPs play an important role in regulating the activity of the secreted metalloproteinases (collagenases, stromelysins, gelatinases). Two different TIMPS have been well characterized, each capable of inhibiting all tested eukaryotic metalloproteinases but showing specific binding to a particular gelatinase at a site distinct from the active site. They influence the activation of the prometalloproteinase and act to modulate proteolysis of extracellular matrix, notably during tissue remodeling and inflammatory processes. On certain cell types, they can exhibit growth factor-like activity, and they can inhibit the tumorigenic and metastatic phenotype of cancer cells.

Amino Acid Sequence↗
PubMed1992

[Studies of distribution of subtypes of transferrin, group-specific component, alpha 1-antitrypsin in gastric cancer patients from Shanghai area].

The genetic polymorphism of transferrin (Tf) and alpha 1-Antitrypsin (alpha 1-AT) in 202 gastric cancer patients and 202 controls in Shanghai Hans were analyzed by isoelectric focusing. In transferrin, the phenotype frequency of C1C1 and gene frequencies of c1 and c2 were 0.3713, 0.5718 and 0.4109 respectively in gastric cancer patients, and 0.5149, 0.6782 and 0.2970 separately in controls. The frequencies of the c1c1 phenotype and the C1 gene increased significantly (p < 0.01) among the controls, while the frequency of the C2 gene greatly increased (p < 0.01) among the patients. The frequencies of the C2C2 in gastric cancer patients and controls were 0.2228 and 0.1436 respectively, showing a significant difference between them (p < 0.05). The genetic polymorphisms of group-specific component (Gc) in 200 gastric cancer patients and 200 controls in Shanghai Hans were studied with isoelectric focusing followed by immunofixation. The Gc1F1F phenotype frequency and 1Fgene frequency were 0.22 and 0.4375 in gastric cancer patients, and 0.14 and 0.3600 in controls, respectively. The frequencies of the Gc1F1F phenotype and the 1F gene were significantly increased (p < 0.05) among the patients. In alpha 1-Antitrypsin, there was no significant difference in phenotype frequencies and gene frequencies between the patients and controls. The data reported here indicate that the gastric cancer is associated positively with TfC2 and Gc1F, and negatively with TfC1. These facts support the notion that cancerogenesis is a multi-step process controlled by multifactorial inheritance.

Adult↗
PubMed1991

[The effects of upstream region of SUC2 gene on its expression].

A series of deletions were made at upstream region of SUC2 gene with the direction from about -900 bp to the initiation codon. The DNA fragments, which contain SUC22 gene and its deleted upstream region, were inserted into multicopy plasmid. After transforming resulted plasmid into SUC strain, the invertase activities produced by the transformants were determined. Under glucose repressing condition, the glycosylated invertase produced by transformants with deletion from -636 bp to -179 bp of SUC2 gene were gradually increased. The transformants with deletion down to -223 bp and -179 bp could produce about 100 times higher glycosylated invertase activity as compared to wild type. Under glucose derepressing condition, the glycosylated invertase produced by transformants with deletion from -395 bp to -179 bp of SUC2 gene were only slightly more than that produced under glucose repressing condition. Under either glucose repressing or derepressing condition, the transformants with deletion at -89 bp and -41 bp produced only a little of glycosylated invertase, while they produced remarkably higher nonglycosylated invertase activity.

Amino Acid Sequence↗
PubMed1990

Transcriptional regulation of glutamine synthetase gene expression by dexamethasone in L6 muscle cells.

Dexamethasone increases glutamine synthetase activity and mRNA abundance in L6 muscle cells in culture, apparently by a glucocorticoid receptor-mediated process. The data in this report reveal that increased glutamine synthetase mRNA abundance is attributable at least in part to an enhanced rate of transcription of the glutamine synthetase gene. "Nuclear runoff" assays of glutamine synthetase gene expression were performed with purified myonuclei from dexamethasone-treated or untreated L6 skeletal muscle cells. These assays showed glutamine synthetase transcription to be increased approximately 2-fold as early as 1 h after incubation of cells with dexamethasone (10(-7) M); there was no increase in the rate of transcription of the beta-tubulin gene, which served as a control. The increase in glutamine synthetase gene transcription correlates with increased glutamine synthetase enzymatic activity after dexamethasone treatment. Studies with actinomycin D indicated that the half-life of glutamine synthetase mRNA (7-8 h) is not altered by dexamethasone. Therefore, the degradation of glutamine synthetase mRNA is not affected by dexamethasone, and the increased glutamine synthetase mRNA level is attributable to increased transcription. The dexamethasone-mediated increase in glutamine synthetase mRNA abundance is glucocorticoid receptor-mediated; RU38486 (a glucocorticoid receptor blocker) completely blocked the effect of dexamethasone. The dexamethasone-mediated increase in glutamine synthetase gene transcription and steady-state mRNA level was not blocked by cycloheximide, indicating a direct effect.

Blotting, Northern↗
PubMed1990

Glutamine regulates glutamine synthetase expression in skeletal muscle cells in culture.

Metabolite control of glutamine synthetase expression (by glutamine) was studied in L6 skeletal muscle cells. Depletion of glutamine from the culture medium for 24 hours resulted in a 3-4-fold increase in glutamine synthetase activity. This effect was blocked by cycloheximide but not by actinomycin D. Addition of glutamine to L6 cells maintained in glutamine-free medium caused a rapid return of glutamine synthetase activity to the control level. As reported, dexamethasone caused a striking increase in the glutamine synthetase mRNA level. In contrast, neither depletion nor addition of glutamine caused a change in the glutamine synthetase mRNA level. Therefore, regulation of glutamine synthetase by glutamine is exerted at a post-transcriptional level.

Animals↗