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K Zhang

Publications and source records attributed to K Zhang.

At least 451 records · Page 25Linked to original sources
PubMed1989

Retroviruses expressing different levels of the normal epidermal growth factor receptor: biological properties and new bioassay.

Two retroviral DNAs that encode the normal human epidermal growth factor (EGF) receptor hEGFR have been generated by inserting a hEGFR cDNA into two different retroviral vectors. One DNA (pCO11-EGFR-neo) also contained a linked selectable marker gene (neoR). The other (pCO12-EGFR) only expresses hEGFR. When introduced into NIH3T3 cells, the two DNAs and the viruses derived from them induced a fully transformed phenotype, including focal transformation and growth in agar or low serum, but transformation depended entirely upon EGF being present in the growth medium. Compared with pCO11-EGFR-neo, pCO12-EGFR induced EGF-dependent transformation 2-5 times more efficiently and expressed higher numbers of receptors (4 x 10(5) vs. 1 x 10(5) EGF receptors per cell). The results indicate that transforming potential is directly related to the number of EGF receptors. In defined, serum-free medium that contained only very low concentrations of insulin (0.6 microgram/ml) and transferrin (0.6 micrograms/ml), hEGFR-virus infected cells were able to grow with EGF as the only growth factor. Moreover, daily incubation of the cells with EGF for only 30 min was sufficient to induce growth. NR6 cells, which lack endogenous EGF receptors, were transformed as efficiently as NIH3T3 cells by the hEGFR virus. The dose-dependent growth response to EGF of infected NR6 cells grown in serum-free medium can be used as a highly sensitive bioassay for the quantitative assessment of EGF and transforming growth factor type alpha (TGF alpha). This bioassay is at least as sensitive as previously reported radioimmunoassays and can measure a much wider concentration range (10 pg-100 ng/ml). Uninfected NR6 cells or NR6 cells infected by helper virus alone can be used as controls for the EGF specificity of growth stimulation.

Biological Assay↗
PubMed1989

Structure and expression of the rat class I alcohol dehydrogenase gene.

Clones containing the rat class I alcohol dehydrogenase (ADH) gene were isolated from a Charon 4A genomic library. The gene spans approximately 13 kb and comprises nine exons and eight introns. The upstream 436 bp contain canonical TATA and CCAAT sequences, an inverted CACCC box, a TG3 box found in mouse and human ADH promoters, and regions of homology to glucocorticoid response elements. The 5'-untranslated region of the ADH transcript has the potential to form a stable stem-loop structure. The first intron contains an unusual stretch of alternating purines and pyrimidines similar to that found in the same location in the mouse ADH gene. The amino acid insertion found in rat alcohol dehydrogenase results from a shift in the 3' splice junction of the fourth intron which adds an extra three base pairs to the fifth exon. Intron-exon boundaries are otherwise identical to those in mouse and human ADH genes. H4IIE cells stably transfected with plasmids containing the chloramphenicol acetyltransferase (CAT) gene fused behind the first 436 bp of the promoter region express CAT, but the CAT activity is not inducible by dexamethasone. The elements responsible for glucocorticoid stimulation of ADH gene transcription appear to reside outside of this region.

Alcohol Dehydrogenase↗
PubMed1988

The active site of hemerythrin as determined by X-ray absorption fine structure.

Extensive X-ray absorption fine structure measurements and analysis have been made on azidomet- and methemerythrin and on the native forms of oxy- and deoxyhemerythrin. Due to the availability of models that have been synthesized to mimic the active site of hemerythrin, it was possible to make a thorough assessment of the various errors in the structural parameters determined by the analysis. It is found that the largest source of error is the lack of complete transferability of amplitude and phase between the standards and hemerythrin. This is of particular importance in distinguishing the contributions of the second-shell low-Z atoms and, thus, has a substantial influence on the determination of the iron-iron distance. The internal consistencies of the various checks and a new formulation of error analysis for the structural parameters give us confidence in the structure determined for the active site. The main result is that as O2 is released from oxyhemerythrin, the mu-oxo bridge between the two iron atoms in the active site with an Fe-O distance of 1.8 A converts to a mu-hydroxo bridge in deoxyhemerythrin, expanding the Fe-O distance to 2.0 A. The Fe-Fe distance expands proportionally from 3.24 A in oxyhemerythrin to 3.57 A in deoxyhemerythrin so as to keep the Fe-O-Fe bridging angle approximately constant. These conclusions provide experimental support for the structures of oxy- and deoxyhemerythrin proposed previously on the basis of spectroscopic and preliminary X-ray crystallographic data.

Animals↗
PubMed1987

Sequence and S1 nuclease mapping of the 5' region of the dihydrofolate reductase-thymidylate synthase gene of Leishmania major.

The 5' structure of mRNA transcribed from the dihydrofolate reductase-thymidylate synthase (DHFR-TS) gene of the protozoan parasite Leishmania major has been characterized. S1 nuclease mapping identifies a heterogenous 5' structure which is not affected by growth phase or developmental stage. The DNA sequence of the 5' region of the DHFR-TS gene does not reveal homology with other trypanosomatid genes, eukaryotic consensus genetic elements, or the mammalian DHFR promoter element. This latter finding is especially significant as we show that the 5' region of the E. coli DHFR gene exhibits homology to the mammalian DHFR promoter element, despite their greater evolutionary distance.

Animals↗
PubMed1987

Structure of the mouse Adh-1 gene and identification of a deletion in a long alternating purine-pyrimidine sequence in the first intron of strains expressing low alcohol dehydrogenase activity.

The ethanol-active alcohol dehydrogenase (ADH-A2) expressed at high levels in mouse liver is encoded by the Adh-1 gene. Inbred strains differ in the amount of ADH-A2 expressed. We report here the cloning and sequencing of the Adh-1 genes from mouse strains that express high and low amounts of ADH-A2 in liver (strains YBR/Ki and Balb/c respectively). The gene contains nine exons, and encodes an ADH-A subunit identical to that encoded by the cDNA isolated from DBA/2J, a strain with low liver ADH activity. This demonstrates that the difference between strains in liver ADH activity is not due to differences in the amino acid sequence of the ADH-A2. The 5'-nontranslated region and at least the first 225 bp 5' to the transcriptional start point are identical in both strains. We have found restriction fragment length polymorphisms in the Adh-1 gene that correlate with the level of expression of ADH-A2 in different strains. One of these RFLPs is within a remarkably long (288 bp) strictly alternating purine-pyrimidine sequence located in the first intron. This region in YBR/Ki contains 25 copies of the sequence ATGT(A/G)T (four of them inverted), which closely resembles important elements in the SV40 enhancer region. Balb/c mice, which express Adh-1 at lower levels, have a deletion that removes 101 bp of this sequence and also have several transition mutations; the comparable region has nine fewer ATGT(A/G)T repeats. These results suggest that the difference in gene expression may be due to differences in these hexamers or in other portions of the alternating purine-pyrimidine sequences, rather than in cis-acting sequences in the proximal 5' (promoter) region.

Alcohol Dehydrogenase↗
PubMed1987

Genetic control of liver alcohol dehydrogenase expression in inbred mice.

The expression of the mouse Adh-1 gene which encodes the ADH-AA isoenzyme of liver alcohol dehydrogenase is under genetic control. The content of alcohol dehydrogenase in the C57BL inbred strain of mice is about twice that in DBA mice. In order to examine the mechanism for control of liver alcohol dehydrogenase expression in mice, we have isolated liver RNA from high and low enzyme activity strains and quantified the content of ADH mRNA with the ADH-A cDNA that was recently cloned in our laboratory. The content of ADH-A mRNA in liver correlates well with enzyme activity in the mouse strains; hence, the expression of Adh-1 appears to be under transcriptional control. A restriction fragment polymorphism was found in mouse liver DNA which correlates with the content of ADH-AA in the high and low ADH activity strains.

Alcohol Dehydrogenase↗
PubMed1987

Use of pedicled omentum in oesophagogastric anastomosis: analysis of 100 cases.

According to reports from our country, leakage occurs in about 5% of oesophagogastric anastomoses despite the numerous improvements in operative techniques, including methods of anastomosis in recent years. From October 1979 to May 1984, 128 cases of oesophageal or gastric cardiac cancer were operated on, and pedicled omentum was used to reinforce the oesophagogastric anastomosis in 100 cases, without any postoperative anastomotic leakage.

Adenocarcinoma↗