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J K Liu

Publications and source records attributed to J K Liu.

At least 55 records · Page 3Linked to original sources
PubMed1998

The absence of strand-specific repair for the DNA polymerase pol gene in Deinococcus radiodurans.

Deinococcus radiodurans is characterized by its extreme resistance to ionizing radiation. Although Mn+2 was taken up by the cells at a high speed, the absorption of Mn+2 by the cells did not affect their survival rate when irradiated by UV light. However, the Mn-induced-cell-division (Mn-CD) cells do lose their resistance to UV radiation. This can be explained by the fact that the Mn-CD cells were less efficient to remove pyrimidine dimers on damaged DNA. We also found that there is no strand-specific repair of the pol gene in this organism.

DNA Damage↗
PubMed1997

Dlx genes encode DNA-binding proteins that are expressed in an overlapping and sequential pattern during basal ganglia differentiation.

The Dlx gene family encodes homeodomain proteins that are required for forebrain and craniofacial development. Towards elucidating the roles for each of these genes, we have isolated cDNA clones encoding the full-coding sequence for murine Dlx-5 and partial coding sequence for murine Dlx-6. Three different classes of sense Dlx-5 cDNA clones were characterized, two of which lack the homeobox. We also identified an antisense Dlx-6 transcript. Genomic analysis shows that the Dlx-5 and -6 genes are linked. Biochemical analysis using gel shift assays demonstrate that DLX-1, -2 and -5 have very similar DNA-binding properties. The expression of Dlx-1, -2, -5, -6 and antisense Dlx-1 and -6 was studied in the midgestation mouse brain. We found that the Dlx genes are expressed in overlapping patterns at different stages of differentiation within the primordia of the basal ganglia. Dlx-1 and -2 are expressed in the least mature cells (in the ventricular and subventricular zones). Dlx-5 appears to be co-expressed with Dlx-1 and -2 in the SVZ, but is also expressed in the postmitotic cells of the mantle. Dlx-6 expression is strongest in the mantle. Antisense Dlx-1 and -6 have their highest expression in the SVZ. These results suggest that each of these Dlx genes may have a distinct role in different steps of differentiation in the basal ganglia.

Amino Acid Sequence↗
PubMed1997

Identification of a copper-sensitive ascorbate peroxidase in the unicellular green alga Selenastrum capricornutum.

Extracts from the unicellular green alga Selenastrum capricornutum exhibit high superoxide dismutase activity, but only traces of catalase activity. The excess hydrogen peroxide (H2O2) generated by the superoxide dismutase in S. capricornutum may be degraded by a unique peroxidase. This peroxidase has a high specificity for ascorbate as its electron donor. The enzyme has an optimum pH at 8, is insensitive to cyanide and is inhibited by oxine. Addition of low concentrations of copper to algal cultures stimulates the peroxidase activity threefold. This enzymatic system could be used as a sensitive bioindicator for copper in fresh water.

Ascorbate Peroxidases↗
PubMed1997

The role of nitrogenase in a cyanide-degrading Klebsiella oxytoca strain.

It is well known that the major function of nitrogenase is to fix atmospheric nitrogen. However, cyanide can also serve as a subtrate for nitrogenase and can be reduced to CH4 and NH4+. A cyanide-degrading Klebsiella oxytoca strain was isolated from cyanide contaminated water. This isolate was also found to have a nitrogen-fixation capability. Nitrogenase activities in this organism could be induced by KCN. However, there was no significant difference of the induction effect between 1 mM KCN and 5 mM KCN. It was found that the cyanide-degrading ability of this isolate could be inhibited by multicopy hybrid pGR112 nif-containing plasmids. Comparing the wild type K. oxytoca strain with the pGR112 plasmid transformed strain, a typical diauxic growth of the wild type strain was observed in a medium containing NH4Cl and KCN. Although the nif plasmid transformed strain also exhibited diauxic growth in the same medium, a much longer second lag phase was noted. In addition, methane, the nitrogenase reduction end product of cyanide, could be detected on cyanide-containing growth cultures. Ammonium chloride, a repressor of nitrogenase gene expression, was consumed prior to KCN in both strains. Again, the degradation of KCN in the pGR112 transformed strain occurred only under loose control of the nitrogenase gene. These findings strongly suggest that nitrogenase may be the sole cyanide-degrading enzyme in this organism.

Bacterial Proteins↗
PubMed1996

Simultaneous determination of cholecystokinin-like immunoreactivity and dopamine release after treatment with veratrine, NMDA, scopolamine and SCH23390 in rat medial frontal cortex: a brain microdialysis study.

The release of cholecystokinin (CCK) and dopamine (DA) was measured simultaneously in the medial frontal cortex of the rat using an in vivo microdialysis technique coupled to either enzyme immunoassay or high performance liquid chromatography with electrochemical detection method. Basal levels of CCK-like immunoreactivity (CCK-LI) and DA in the dialysates were 0.29 +/- 0.05 pg/50 microliters and 4.98 +/- 0.56 fmol/20 microliters respectively. After perfusion of 100 micrograms/ml veratrine into rat medial frontal cortex through the microdialysis probe, the release of those neurotransmitters was significantly enhanced. Perfusion of 10 mM NMDA induced significant increases of CCK-LI and DA levels. Co-perfusion of 1 mM SCH23390, a D1 receptor antagonist, suppressed NMDA-evoked CCK-LI release and slightly raised NMDA-evoked DA release. Treatment with scopolamine, a muscarinic receptor antagonist, suppressed veratrine-induced CCK-LI and DA release, but did not change NMDA-evoked CCK-LI and DA release. These results suggest that NMDA may regulate CCK-LI release through the activation of D1 receptor existing on the afferent CCK neurons or interneurons in rat medial frontal cortex, and changes of endogenous CCK release may be involved in NMDA receptor-mediated long-term potentiation.

Animals↗
PubMed1996

Sequence, organization, and transcription of the Dlx-1 and Dlx-2 locus.

There are at least five murine Dlx genes that are related to the Drosophila Distal-less homeobox gene. The Dlx genes are primarily expressed in the developing forebrain, derivatives of the cranial neural crest and restricted epidermal craniofacial and limb domains. Dlx-2 is required for differentiation of subsets of cranial neural crest and forebrain cells. Previous genomic studies have shown that Dlx-1 and Dlx-2 are linked on mouse chromosome 2, near the HoxD cluster. Here we report a detailed analysis of the nucleotide sequence (approximately 14 kb), organization, and transcription of the murine Dlx-1 and Dlx-2 locus. In addition, we show that Dlx-1 makes multiple sense transcripts and at least one antisense transcript, whereas Dlx-2 makes one major transcript. The sequence of the human Dlx-2 gene is reported and is compared to that of the murine gene. Finally, sequence analysis of the deduced protein sequences reveals several candidate functional domains.

Amino Acid Sequence↗
PubMed1996

Detection of basal acetylcholine release in the microdialysis of rat frontal cortex by high-performance liquid chromatography using a horseradish peroxidase-osmium redox polymer electrode with pre-enzyme reactor.

To determine the basal acetylcholine level in the dialysate of rat frontal cortex, a horseradish peroxidase-osmium redox polymer-modified glassy carbon electrode (HRP-GCE) was employed instead of the conventional platinum electrode used in high-performance liquid chromatography-electrochemical detection (HPLC-ED). In initial experiments, an oxidizable unknown compound interfered with the detection of basal acetylcholine release on HPLC-HRP-GCE. An immobilized peroxidase-choline oxidase precolumn (pre-reactor) was included in the HPLC system, to eliminate the interference from the unknown compound. This combination could detect less than 10 fmol of standard acetylcholine and basal acetylcholine levels in the dialysate from a conventional concentric design microdialysis probe, without the use of cholinesterase inhibitor, and may facilitate physiological investigation of cholinergic neuronal activity in the central nervous system.

Acetylcholine↗
PubMed1996

Impaction of a mandibular permanent lateral incisor associated with fused primary teeth: a case report.

Although anesthetic and functional problems created by fused primary teeth are relatively transient, occlusal development should be monitored to prevent abnormal delays in the eruption of the permanent successors. This report describes an unusual case in which horizontal impaction of the permanent mandibular left lateral incisor was associated with fusion of the primary mandibular left lateral incisor and canine. After the fused primary tooth was extracted, the impacted lateral incisor was able to erupt without the aid of orthodontic forces. Early detection eliminated the need for surgical intervention at a later stage.

Child↗
PubMed1996

Expression of polyphosphate kinase inhibits the glucose uptake in Escherichia coli.

This paper examines the effects of phosphate pool and expression of polyphosphate kinase on glucose uptake by expressing the polyphosphate kinase under the control of lac promoter. The E. coli transformant of pL1, containing an IPTG controllable element for polyphosphate kinase expression, showed that the total intracellular phosphate significantly increased. However, the rate of glucose uptake by the resting plasmid-bearing cells with IPTG induction significantly decreased. These findings suggest that the polyphosphate can not directly function as an energy source in E. coli or at least not as a good energy supplier.

Biological Transport↗
PubMed1995

Replacing protein in corn-soybean turkey diets with methionine and lysine.

The extent to which dietary protein can be minimized by using Met and Lys supplements for market turkeys has been investigated in three experiments involving 2,750 birds. Large White (Nicholas) male turkey poults were fed corn-soybean meal diets of varying protein level to supply Lys from 80 to 120 of NRC (1984) from day-old to 18 wk of age. Performance with diets of 90% NRC Lys was equal to that with diets of higher Lys, provided that SAA were at 100% of NRC. Up to .2% Lys.HCl could be substituted into the 100 or 90% of NRC diets with no depression in performance, suggesting that the other essential amino acids were present in adequate amounts. When turkeys were fed diets of 85% of NRC (1984) Lys, maximum growth and breast meat yield were obtained with supplemental SAA at 100% during 0 to 18 wk of age and Lys at 100% during 12 to 18 wk of age. The requirements for other amino acids were supplied by diets formulated to provide 85% of the Lys requirement from protein. These values were for turkeys subjected to 18 C during final growout; they were not adequate in warmer temperatures.

Animal Feed↗
PubMed1994

Effect of physostigmine on relative acetylcholine output induced by systemic treatment with scopolamine in in vivo microdialysis of rat frontal cortex.

By means of an in vivo brain microdialysis, the effect of different concentrations of physostigmine on the acetylcholine level in the dialysate of rat frontal cortex was studied. Perfusion of the various degrees of physostigmine (eserine) concentration (10 nM-10 microM) into the cortex through the dialysis membrane increased the basal acetylcholine level in a dose-dependent manner. In the presence of 10 nM, 0.1 microM and 10 microM physostigmine in the perfusate, systemic treatment with scopolamine (0.5 mg/kg, i.p.) increased 200, 270 and 510%, respectively, the relative acetylcholine level in the dialysates in comparison with the corresponding basal levels, while in the absence of physostigmine the treatment increased it only 40%. From these results, it appears that perfusion of physostigmine at a variety of concentrations, changes not only the basal level of acetylcholine induced by the inhibition of acetylcholinesterase but also the relative acetylcholine output induced by systemic treatment with scopolamine.

Acetylcholine↗
PubMed1994

DLX-2, MASH-1, and MAP-2 expression and bromodeoxyuridine incorporation define molecularly distinct cell populations in the embryonic mouse forebrain.

Recently, the Dlx family of homeobox genes have been identified as candidates for regulating patterning and differentiation of the forebrain. We have made a polyclonal antiserum to the protein product of the Dlx-2 gene. Using this antiserum, we have characterized the spatial and temporal pattern of DLX-2 protein expression during murine development and in the adult mouse brain. These studies demonstrate that, like the mRNA from the Dlx-2 gene, DLX-2 protein is expressed in mouse embryonic forebrain, limbs, tail, genital tubercle, and branchial arches. Within the embryonic forebrain, DLX-2 protein is expressed within specific transverse and longitudinal domains. Analysis of expression within the wall of the forebrain shows that DLX-2 is expressed in proliferative regions including the ventricular and subventricular zones. DLX-2 is expressed in the same cells as MASH-1, a marker of relatively undifferentiated cells, but in a reciprocal fashion to MAP-2, a marker of terminal neuronal differentiation. A number of DLX-2-expressing cells, but not all, can be labeled with bromodeoxyuridine (BrdU). Using the patterns of DLX-2, MASH-1, MAP-2 expression, and bromodeoxyuridine incorporation, we identify four molecularly distinct populations of cells that may correspond to different stages of neuronal differentiation in the mouse basal forebrain, in which DLX-2 is expressed at the transition from proliferation to terminal differentiation.

Animals↗
PubMed1993

A new factor related to TATA-binding protein has highly restricted expression patterns in Drosophila.

The TATA-binding protein TBP is necessary for the transcription of eukaryotic genes. Multi-protein complexes formed by TBP and different TBP-associated factors are involved in the initiation of transcription by polymerases I and II, and probably III as well. During the formation of an active initiation complex, TBP makes specific contacts with other proteins, for example TFIIB and RNA polymerase II (refs 2-4). Here we describe the cloning and characterization of a Drosophila gene product with considerable sequence similarity to TBP and a highly restricted expression pattern in the embryo. This TBP-related factor is a DNA-binding protein but is not likely to be a basal transcription factor. Our results suggest that TBP-related factor is a sequence-specific transcription factor that shares the DNA-binding properties of TBP.

Animals↗
PubMed1993

[Hemodynamic changes after combination operation in cirrhotic patients with portal hypertension].

Hemodynamic changes of the portal system were investigated with pulsed Doppler ultrasound device in normal controls and patients with portal hypertension treated by combination surgical technique. It was found that the diameter and blood flow of the portal vein, splenic vein and superior mesenteric vein were larger than those of normal controls. Whereas the velocity of blood flow was lower than that of normal controls. FPP decreased by 31.3% after combination operation: 7.3% after splenectomy; There was a positive correlation between FPP and blood flow of splenic artery. The portal blood flow decreased by 42% after disconnection and 62.6% after combination operation. The blood flow of superior mesenteric vein after disconnection increased by 38%. The decrease of portal blood flow after disconnection was positively correlated with the blood flow of the splenic vein. Combination operation is a simple and rational procedure with a good effect in stopping hemorrhage, reducing portal vein pressure, and preventing recurrence of esophageal varices.

Adult↗
PubMed1992

Translational control of pyrC expression mediated by nucleotide-sensitive selection of transcriptional start sites in Escherichia coli.

Expression of the pyrC gene, which encodes the pyrimidine biosynthetic enzyme dihydroorotase, is negatively regulated by pyrimidine availability in Escherichia coli. To define the mechanism of this regulation, an essential regulatory region between the pyrC promoter and the initial codons of the pyrC structural gene was identified. Mutational analysis of this regulatory region showed that the formation of a hairpin at the 5' end of the pyrC transcript, which overlaps the pyrC ribosome binding site, is required for repression of pyrC expression. Formation of the hairpin appears to be controlled by nucleotide-sensitive selection of the site of pyrC transcriptional initiation. When the CTP level is high, the major pyrC transcript is initiated with this nucleotide at a position seven bases downstream of the pyrC -10 region. This transcript is capable of forming a stable hairpin at its 5' end. When the CTP level is low and the GTP level is high, conditions found in cells limited for pyrimidines, the major pyrC transcript is initiated with GTP at a position two bases further downstream. This shorter transcript appears to be unable to form a stable hairpin at its 5' end. These results suggest a model for regulation in which the longer pyrC transcripts are synthesized predominantly under conditions of pyrimidine excess and form the regulatory hairpin, which blocks pyrC translational initiation. In contrast, the shorter pyrC transcripts are synthesized primarily under conditions of pyrimidine limitation, and they are readily translated, resulting in a high level of dihydroorotase synthesis. The data also indicate that a low level of pyrimidine-mediated regulation may occur at the level of transcriptional initiation.

Base Sequence↗
PubMed1992

Isolation and partial purification of cytochrome oxidases from Bacillus thuringiensis subsp. israelensis HD-567.

Analyses of the cell membrane fractions by spectral absorbance revealed the presence of cytochrome c and three cytochrome oxidases in Bacillus thuringiensis subsp. israelensis HD-567-cytochromes a+a3, d, and o. A modified procedure was used to purify the cytochrome c:o complex from this organism. The oxidase complex was first solubilized from a sonic-disrupted cell membrane fraction (R3 fraction) using deoxycholate and KCl. The resulting soluble fraction was further purified by Sephadex G-50 gel filtration and DEAE ionexchange chromatography. TMPD oxidase specific activity and cytochrome concentration were assayed to monitor the purification procedures. The F7 fraction (obtained after G-50 chromatography) contained cytochrome c (0.44 nmole/mg protein), cytochrome a+a3 (0.26 nmole/mg protein), and cytochrome o (0.38 nmole/mg protein), which had 6-fold, 3.4-fold and 18.9-fold increase, respectively, by comparison with the original R3 fraction. The TMPD oxidase specific activity of the F7 fraction also increased 4.8 fold. The F8 fraction (obtained after the final DEAE chromatography) contained a cytochrome c:o complex only (cytochrome c, 0.46 nmole/mg protein; cytochrome o, 0.16 nmole/mg protein), but no cytochrome a+a3 was found. Both the TMPD oxidase specific activity and the cytochrome o were attenuated greatly in comparison with the F7 fraction. SDS-PAGE analysis revealed that the F7 fraction contained numerous protein components, while the F8 fraction contained only a prominent major protein of 113.5 kD thought to be the cytochrome c:o complex, and a minor polypeptide (MW = 65.8 kD). Although the final DEAE procedure removed many undesired polypeptides, TMPD oxidase activity and cytochrome o component were also lost greatly. Kinetic studies of this cytochrome c:o complex is in progress in our laboratory.

Bacillus thuringiensis↗
PubMed1992

Effect of gluco- and mineralocorticoids on gene expression of atrial natriuretic peptide by rat atria in vivo.

The effect of gluco- and mineralocorticoids on atrial natriuretic peptide (ANP) gene expression as well as plasma sodium and potassium concentrations was studied in both intact and adrenalectomized Wistar rats. Atria total RNA was extracted with cold phenol method and hybridized to alpha-32P labeled rat ANP-cDNA probe. The ANP gene transcripts in intact rats receiving dexamethasone and in adrenalectomized rats receiving both dexamethasone and deoxy-corticosterone increased by twofold, while there were no significant changes in the other groups. There were no parallel correlations between the rise of corticoid hormones-induced plasma Na+ concentration and the enhancement of rANP-mRNA level. The results suggest that glucocorticoids, when used together with mineralocorticoids, may directly increase ANP gene expression, whereas administration of mineralocorticoids alone has no effect on ANP gene expression.

Adrenalectomy↗