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Biomedical subjects

C Q Chen

Publications and source records attributed to C Q Chen.

28 records · Page 2Linked to original sources
PubMed1988

Chemical synthesis and cloning of secretin gene.

A DNA duplex coding for the 27 amino acids of secretin has been synthesized and cloned. In designing the sequence of the gene, computer analysis has been applied. The following factors have been considered: selection of codon usage in favour of expression in yeast; design of various sites useful in gene cloning, gene modification and expressed product purification; avoiding the repeat sequences which may interfere in the ligation of the synthetic fragments. The synthesis involved preparation of 12 oligodeoxyribonucleotides (12-mer to 24-mer in length) by phosphate triester and phosphite triester method, purification by polyacrylamide gel electrophoresis (PAGE). A new plasmid pWS1 was constructed by insertion of the enzymatic ligated gene fragment into plasmid pWR13.

Base Sequence↗
PubMed1984

The cloning and expression of the synthetic leu-enkephalin gene in E. coli.

The synthetic leu-enkephalin (LEK) gene was joined with pBR322 and transformed to E. coli. The recombinant plasmids containing the LEK gene were selected by colony hybridization, and characterized by restriction mapping and Southern's technique. The lac operon was used to control the expression of the LEK gene. A recombinant plasmid, pEL 103, in which the lac operon and LEK gene are transcribed in the same direction, produces LEK in E. coli. The level of LEK detected by radioimmunoassay reaches 426 ng per mg of bacterial protein.

Cloning, Molecular↗
PubMed1984

Synthesis of the leu-enkephalin gene.

The synthesis of Leu-enkephalin gene by an alternative approach was described in this paper. The sequence of the synthetic gene, 26 base-pairs in length, was derived from the amino acid sequence of the hormone peptide Leu-enkephalin. It bears single-stranded cohesive termini for the restriction endonucleases EcoR I and BamH I so that it may be inserted into a pBR 322 plasmid. The 4 deoxyoligonucleotide fragments, varying in length from octanucleotide to octadecanucleotide, were synthesized by an improved phosphotriester method developed in our laboratory. All chemically synthetic fragments were pure and had the correct sequences. The assembly of the Leu-enkephalin gene was carried out in a one-step ligation reaction catalysed by T4-DNA ligase with good yield. Finally, the purified products from polyacrylamide gel electrophoresis had the correct joining-points as predicted.

DNA Ligases↗
PubMed1983

Total synthesis of yeast alanine transfer ribonucleic acid.

By a combination of chemical and enzymatic methods, small oligonucleotides with lengths varying from 2 to 8 nucleotides were synthesized from mononucleotides. The small oligonucleotides were then ligated with T4 RNA ligase into six large oligonucleotides (9 to 19 nucleotides long) which were further ligated to form two half molecules with 35 and 41 nucleotides respectively. Finally, the two synthetic half molecules were annealed and ligated to obtain the whole molecule of yeast alanine tRNA (tRNAAlay). Prior to this, two semi-syntheses were performed, i.e. ligation of the synthetic 5'-half molecule with the natural 3'-half molecule and that of the natural 5'-half molecule with the synthetic 3'-half molecule. Both the semi-synthetic tRNAAlay and the synthetic tRNAAlay occupy the same position as the natural tRNAAlay after electrophoresis on a 20% polyacrylamide gel. They have the same chemical composition (containing 9 modified nucleotides of 7 different species) and structure as the natural tRNAAlay and are biologically active, i.e. accepting and transferring alanine into proteins in a cell-free protein synthesizing system, the accepting activity of the synthetic product is 52-66% of that of the natural tRNAAlay and 91-106% of that of the reconstituted product of the two natural half molecules. The incorporation activity of alanine into proteins of the synthetic 3H-alanine tRNAAlay is 63%, corresponding to 91% of that of the natural tRNAAlay and 115% of that of the reconstituted product of the two natural half molecules. To the best of our knowledge, this is the first time that a natural RNA with biological activity is synthesized.

Base Sequence↗
PubMed1983

Synthesis of the 5'-half molecule of yeast alanine tRNA.

In this paper, we report the synthesis of the 5'-half molecule of yeast alanine tRNA (tRNAAlay) by ligating three oligonucleotide fragments corresponding to the nucleotide sequences 1-13, 14-22 and 23-35 respectively under the catalysis of T4 RNA ligase (Fig. 1). Because of the high purity of the oligonucleotide fragments and the excellent quality of T4RNA ligase and polynucleotide kinase we prepared, the isolation steps were simplified and the overall yields were much higher. The ligating yield of the docosamer (IV) was 75%, that of the pentatriacontamer (V), 90%, and the isolated yield of the final product was 21% calculated on the basis of the tridecamer (III) used in the first reaction. Under the action of T4 RNA ligase the synthetic 5'-half molecule was joined with the natural 3'-half molecule forming a semi-synthetic tRNAAlay, which possessed the biological activities of both accepting (3H)-alanine and incorporating it into proteins. The correctness of the structure of the synthetic 5'-half molecule was verified by both chemical analysis and biological activity assay.

Base Sequence↗
PubMed1979

Computed tomographic evaluation of para-aortic hematoma following translumbar aortography.

Computed tomography provides an objective means of studying needle passage and para-aortic hematoma formation following translumbar aortography (TLA). CT scans from the puncture site to the aortic entry site were done in 13 patients before and after catheter removal to evaluate the incidence and extent of hematoma formation. Eleven (87%) demonstrated para-aortic hematomas following TLA; 8 were confined to the left para-aortic area and 3 involved both sides. The catheter passed through the left kidney in one patient; however, no hematoma was observed.

Aortic Diseases↗
PubMedDate not supplied

Preparation of human serum albumin microspheres by a novel acetone-heat denaturation method.

Human serum albumin (HSA) microspheres have been produced in the size range of 200 nm to 10 microns by the controlled addition of acetone to an aqueous solution of HSA, followed by stabilization of the formed microspheres at an elevated temperature. Microspheres produced by this acetone-heat denaturation method could be stabilized at relatively low temperatures (75 degrees C) over a short time period (15-30 min). The acetone-heat denaturation method is different from the traditional oil/water technique for preparation of HSA microspheres, both in terms of production method and the avoidance of high temperatures (> 100 degrees C) and extended heating times (> 30 min) for stabilization. This paper describes the influence of process conditions, such as volumes of acetone and HSA concentration, on the formation of the microspheres and their morphological characteristics. A loading efficiency of 8 per cent was achieved for the HSA microspheres when using rose bengal as a model compound. The release of rose bengal from the microspheres in phosphate buffered saline at 37 degrees C was dependent on the presence of the surfactant Tween 80, and varied from a 5 per cent release in 14 days in the absence of surfactant to a 50 per cent release in 8 h in the presence of surfactant.

Acetone↗