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L Kang

Publications and source records attributed to L Kang.

52 records · Page 3Linked to original sources
PubMed1991

Analysis of cDNAs of the proto-oncogene c-src: heterogeneity in 5' exons and possible mechanism for the genesis of the 3' end of v-src.

To further characterize the gene structure of the proto-oncogene c-src and the mechanism for the genesis of the v-src sequence in Rous sarcoma virus, we have analyzed genomic and cDNA copies of the chicken c-src gene. From a cDNA library of chicken embryo fibroblasts, we isolated and sequenced several overlapping cDNA clones covering the full length of the 4-kb c-src mRNA. The cDNA sequence contains a 1.84-kb sequence downstream from the 1.6-kb pp60c-src coding region. An open reading frame of 217 amino acids, called sdr (src downstream region), was found 105 nucleotides from the termination codon for pp60c-src. Within the 3' noncoding region, a 39-bp sequence corresponding to the 3' end of the RSV v-src was detected 660 bases downstream of the pp60c-src termination codon. The presence of this sequence in the c-src mRNA exon supports a model involving an RNA intermediate during transduction of the c-src sequence. The 5' region of the c-src cDNA was determined by analyzing several cDNA clones generated by conventional cloning methods and by polymerase chain reaction. Sequences of these chicken embryo fibroblast clones plus two c-src cDNA clones isolated from a brain cDNA library show that there is considerable heterogeneity in sequences upstream from the c-src coding sequence. Within this region, which contains at least 300 nucleotides upstream of the translational initiation site in exon 2, there exist at least two exons in each cDNA which fall into five cDNA classes. Four unique 5' exon sequences, designated exons UE1, UE2, UEX, and UEY, were observed. All of them are spliced to the previously characterized c-src exons 1 and 2 with the exception of type 2 cDNA. In type 2, the exon 1 is spliced to a novel downstream exon, designated exon 1a, which maps in the region of the c-src DNA defined previously as intron 1. Exon UE1 is rich in G+C content and is mapped at 7.8 kb upstream from exon 1. This exon is also present in the two cDNA clones from the brain cDNA library. Exon UE2 is located at 8.5 kb upstream from exon 1. The precise locations of exons UEX and UEY have not been determined, but both are more than 12 kb upstream from exon 1. The existence and exon arrangements of these 5' cDNAs were further confirmed by RNase protection assays and polymerase chain reactions using specific primers. Our findings indicate that the heterogeneity in the 5' sequences of the c-src mRNAs results from differential splicing and perhaps use of distinct initiation sites. All of these RNAs have the potential of coding for pp60c-src, since their 5' exons are all eventually joined to exon 2.

Amino Acid Sequence↗
PubMed1991

The proto-oncogene c-ros codes for a transmembrane tyrosine protein kinase sharing sequence and structural homology with sevenless protein of Drosophila melanogaster.

Our earlier study predicted that proto-oncogene c-ros codes for a receptor-like tyrosine protein kinase (TPK). To further understand its protein structure and physiological function, we have analysed its expression in various tissues of chicken and have isolated and sequenced cDNA clones containing the entire coding region of the gene. Confirming our earlier study, we found that kidney is the organ that expresses the highest level of c-ros mRNA, in addition, we found a lower level of expression in gonad, thymus, bursa and brain. A distinctive 8.3 kb c-ros mRNA is present in kidney. No detectable amount of c-ros mRNA was found in the rest of tissues examined. Nucleotide sequence of the c-ros cDNA predicts that it codes for a transmembrane (TM) TPK molecule of 2311 amino acids (aa). The extracellular domain consists of 1873 amino acids which share 20 to 43% homology with that of the Drosophila sevenless protein and TPK domains of the two genes have 58 to 74% homology. The extracellular domain containing 37 potential N-linked glycosylation sites is preceded by a 5' hydrophobic sequence resembling a typical signal peptide. An internal hydrophobic domain of 26 amino acids, the presumed transmembrane domain, is followed by a spacer sequence of 58 amino acids, a TPK domain of 270 amino acids and a carboxyl tail of 84 amino acids. Overall, our result indicates that c-ros codes for a glycosylated transmembrane TPK molecule which shares a remarkable sequence and structural homology with that of Drosophila sevenless protein.

Amino Acid Sequence↗
PubMed1990

Purification and characterization of bisulfite reductase (desulfofuscidin) from Desulfovibrio thermophilus and its complexes with exogenous ligands.

A dissimilatory bisulfite reductase has been purified from a thermophilic sulfate-reducing bacterium Desulfovibrio thermophilus (DSM 1276) and studied by EPR and optical spectroscopic techniques. The visible spectrum of the purified bisulfite reductase exhibits absorption maxima at 578.5, 392.5 and 281 nm with a weak band around 700 nm. Photoreduction of the native enzyme causes a decrease in absorption at 578.5 nm and a concomitant increase in absorption at 607 nm. When reduced, the enzyme reacts with cyanide, sulfite, sulfide and carbon monoxide to give stable complexes. The EPR spectrum of the native D. thermophilus bisulfite reductase shows the presence of a high-spin ferric signal with g values at 7.26, 4.78 and 1.92. Upon photoreduction the high-spin ferric heme signal disappeared and a typical 'g = 1.94' signal of [4Fe-4S] type cluster appeared. Chemical analyses show that the enzyme contains four sirohemes and eight [4Fe-4S] centers per mol of protein. The molecular mass determined by gel filtration was found to be 175 kDa. On SDS-gel electrophoresis the enzyme presents a main band of 44 to 48 kDa. These results suggest that the bisulfite reductase contains probably one siroheme and two [4Fe-4S] centers per monomer. The dissimilatory bisulfite reductase from D. thermophilus presents some homologous properties with desulfofuscidin, the bisulfite reductase isolated from Thermodesulfobacterium commune (Hatchikian, E.C. and Zeikus, J.G. (1983) J. Bacteriol. 153, 1211-1220).

Amino Acids↗
PubMed1989

[Effect of calcium channel blocking agents on methacholine-induced airway hyperreactivity in subjects with asthmatic bronchitis, asthma and cor pulmonale].

Methacholine-induced airway reactivity was studied in patients with asthmatic bronchitis, asthma or cor pulmonale during remission and the parameters (especially of cor pulmonale) were significantly higher than those of control subjects. The change was negatively relevant to FEV1 V25 V50 and MMF. The subjects were given two tablets of placebo, verapamil (80mg), nifedipine (20mg) or diltiazem (60mg) orally and double-blindly. In every subject, PC20 and lung functions were tested 2 or 3 hours after administration. These agents did not dilate bronchi. However, airway reactivity to methacholine was attenuated by nifedipine in asthmatic bronchitis and by diltiazem in asthma (P less than 0.05). However all the three agents did not reduce airway reactivity of cor pulmonale.

Adult↗
PubMed1988

Rigid contact lens area and corneal oxygenation.

The corneal area covered by a rigid contact lens under static conditions was calculated for various combinations of lens and corneal diameters. The lens was then assumed to move to various positions on the cornea to find the lens overlap of the corneal area originally covered by the lens. For most clinically practical dimensions, when the contact lens moves to the corneal limbus, a small area of lens overlap remains. This corneal area receives no direct exposure to the external atmosphere and must derive its oxygen via a tear-pumping action by the lens. A method for the calculation of this area is presented. The model is used to explain the appearance of central corneal clouding (CCC), the function of the contact lens peripheral curve, and a possible mechanism for corneal oxygenation during extended wear.

Contact Lenses↗
PubMed1987

Spectroscopic properties of siroheme extracted from sulfite reductases.

Siroheme has been extracted from sulfite reductases and its properties in aqueous solution have been investigated by optical absorption, electron paramagnetic resonance (EPR), and magnetic circular dichroism (MDC) spectroscopy. The absorption spectrum of siroheme exhibits a marked pH dependence, and two pK values, 4.2 and 9.0, were determined by pH titration in the range 2-12. The first pK (4.2) is thought to correspond to the ionization of the carboxylic acid side-chains on the tetrapyrrole rings, and the second pK (9.0) is attributed to displacement of the axial ligand chloride by hydroxide. The binding of the strong field ligands, CO, NO, and cyanide, were investigated by UV-visible absorption and, in the case of the cyanide complex, by low-temperature EPR and MCD spectroscopies. CO and NO were able to reduce and bind to siroheme without additional reducing agent. The EPR spectrum of the isolated siroheme (chloride-ferrisiroheme) exhibits an axial signal with g perpendicular = 6.0 and g parallel = 2.0, typical of high-spin ferric hemes (S = 5/2), whereas the cyanide-complexed siroheme exhibits an approximately axial signal with g perpendicular = 2.38 and g parallel = 1.76 that is indicative of a low-spin ferric heme (S = 1/2). The low-temperature MCD spectra and magnetization data for the as-isolated and cyanide-complexed ferrisiroheme are entirely consistent with the interpretation of the EPR spectra. The results for ferrosiroheme indicate that the siroheme remains high spin (S = 2) and low spin (S = 0) on reduction of the as-isolated and cyanide-complexed siroheme, respectively. The isolated siroheme expressed sulfite reductase activity but the assessable catalytic cycle was much less than that of the native enzyme, showing the importance of the protein environment.

Desulfovibrio↗
PubMed1987

Karyotypic characterization of an established human hepatoma cell line HA22T/VGH.

The karyotype of an established human hepatoma cell line HA22T/VGH was characterized by G-banding. A majority of the 200 cells counted had around 70 chromosomes at passage 24, and 60 at passage 338. Of the 50 cells karyotyped from each of passage 24 and passages 338-339, chromosomes #13 and #18 were absent. The presence of the Y chromosome was reduced dramatically from a mean value of 1.12/cell at passage 24 to 0.12/cell at passages 338-339. In general, most of the chromosomes--particularly chromosomes #5, #7, #9, #15, and #21--tended to be less represented in the course of propagation in vitro. The presence of multiple copies of a normal chromosome in a single cell was quite common for chromosomes #5 and #7 at both early and late passages. Numerous structural rearrangements of the chromosomes were observed.

Carcinoma, Hepatocellular↗
PubMed1984

Characterization of a sulfite reductase from Desulfovibrio vulgaris. Evidence for the presence of a low-spin siroheme and an exchange-coupled siroheme-[4Fe-4S] unit.

We have studied a low-molecular-weight (Mr = 27,200) sulfite reductase from Desulfovibrio vulgaris (Hildenborough, NCIB 8303) with Mössbauer, EPR, and chemical techniques. This sulfite reductase was found to contain one siroheme and one [4Fe-4S] cluster. As purified, the siroheme is low-spin ferric (S = 1/2) which exhibits characteristic EPR resonances at g = 2.44, 2.36, and 1.77. At 150 K, the observed Mössbauer parameters, delta EQ = 2.49 +/- 0.02 mm/s and delta = 0.31 +/- 0.02 mm/s, for the siroheme are typical for low-spin ferric complexes. The [4Fe-4S] cluster is in the 2+ state. The Mössbauer parameters, delta EQ = 0.95 +/- 0.02 mm/s and delta = 0.38 +/- 0.02 mm/s, for the cluster are almost identical to those observed for the [4Fe-4S]2+ cluster in the hemoprotein subunit of the sulfite reductase from Escherichia coli. Similar to the hemoprotein subunit of E. coli sulfite reductase, low-temperature Mössbauer spectra of D. vulgaris sulfite reductase recorded with weak and strong applied fields also show evidence for an exchange-coupled siroheme-[4Fe-4S] unit.

Desulfovibrio↗
PubMed1982

Nitrogen catabolite repression in a glutamate auxotroph of Saccharomyces cerevisiae.

The biosynthesis of asparaginase II in Saccharomyces cerevisiae is subject to nitrogen catabolite repression. In the present study we examined the physiological effects of glutamate auxotrophy on cellular metabolism and on the nitrogen catabolite repression of asparaginase II. Glutamate auxotrophic cells, incubated without a glutamate supplement, had a diminished internal pool of alpha-ketoglutarate and a concomitant inability to equilibrate ammonium ion with alpha-amino nitrogen. In the glutamate auxotroph, asparaginase II biosynthesis exhibited a decreased sensitivity to nitrogen catabolite repression by ammonium ion but normal sensitivity to nitrogen catabolite repression by all amino acids tested.

Amino Acids↗
PubMed1982

Classification of several tobamoviruses isolated in China on the basis of the amino acid composition of their virion proteins.

The amino acid compositions of the virion proteins of several tobamoviruses isolated in China were determined. A classification computed from these and published data of other tobamoviruses was compared with published data of their relatedness assessed using the cDNA:RNA molecular hybridization technique. The classifications are clearly congruent; that based on amino acid composition appears to be best for determining the hierarchical relationships of members within a taxonomic group, rather than for distinguishing between closely related members, whereas nucleic acid hybridization unequivocally places a virus into the appropriate subgroup but is less useful for determining distant relationships.

Amino Acids↗