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Biomedical subjects

A C Chang

Publications and source records attributed to A C Chang.

At least 181 records · Page 10Linked to original sources
PubMed1984

Protein kinases derived from the conditioned media of human peripheral blood mononuclear cells.

Two classes of cyclic nucleotide-independent protein kinase from the conditioned media of human peripheral blood mononuclear cells were detected. The first one was specific for histone, and was not retained by the remazol blue-agarose column. The second one was specific for casein and phosvitin, and was retained by the remazol blue-agarose column. Histone kinase activity was elevated in Con A-conditioned media. These peripheral blood mononuclear cells were subsequently fractionated into adherent and nonadherent cell populations. It was clear that histone kinase was secreted by adherent cells while casein and phosvitin kinases were secreted by nonadherent cells.

Cell Adhesion↗
PubMed1984

Biosynthesis and axoplasmic transport of neurophysins in the hypothalamo-neurohypophysial system of Rana pipiens.

Biosynthesis, axoplasmic transport, and storage of neurophysin in the amphibian (Rana pipiens) magnocellular peptidergic neurosecretory system were studied, and the results were compared with those reported in mammals. After injection of [35S]cysteine into the preoptic recess, light microscopic autoradiography provides evidence that neurons of the preoptic nucleus (PON) synthesize cysteine-rich proteins. The time course of appearance of these [35S]cysteine-labeled proteins in different regions of the hypothalamo-neurohypophysial system was studied by slab gel autoradiography. [35S]Cysteine-labeled proteins were found in the PON less than 1 hr postinjection, whereas a major labeled protein, tentatively identified as the neurophysin, first appeared in the infundibulum and neural lobe 4 hr after the injection. In addition, the labeled neurophysin persisted in the neural lobe throughout the entire observation period of 5 days. The minimum transport rate for neurophysin was calculated as 0.9 mm/hr (22 mm/day) at 25 degrees C. Two different neurophysins (with isoelectric points (pI) 4.9 +/- 0.1, 4.6 +/- 0.1, and Mr = 23,000, 20,100) may be resolved from the neural lobe extracts by isoelectric focusing and SDS-polyacrylamide gel electrophoresis, respectively. In addition to the neurophysin peaks, two radioactive peaks with pI 5.2 and 5.8 may be detected in the preoptic nucleus and the infundibulum as early as 30 min after [35S]cysteine injection. Preliminary conversion studies suggest a putative precursor role for the pI 5.2 protein. The results indicate that in the amphibian peptidergic neurosecretory system, the synthesis of cysteine-rich neurophysin by the preoptic neurons, the transport through the infundibulum, and the storage in the neural lobe proceed similarily to their mammalian counterparts.

Animals↗
PubMed1983

Decay of mRNA in Escherichia coli: investigation of the fate of specific segments of transcripts.

An assay was developed to investigate the fate of specific segments of beta-lactamase (bla) and ompA gene transcripts in Escherichia coli. DNA probes cloned in bacteriophage M13 were treated with an endonuclease capable of cleaving single-stranded DNA, the fragments produced were annealed with total cellular RNA, and the resulting RNA . DNA hybrids were subjected to S1 nuclease treatment and gel fractionation. By using this assay, direct evidence was obtained for 3'-to-5' directionality in the decay of the long-lived mRNA encoded by the ompA gene, and no preferential stability was observed for translated versus untranslated mRNA segments. In the case of bla mRNA, initial cleavage of the full-length transcript was rate limiting, and no decay intermediates were detected. No difference in degradation rate was seen for bla transcripts having variant 3' or 5' termini.

Bacterial Outer Membrane Proteins↗
PubMed1983

A DNA polymorphism in close physical linkage with the proopiomelanocortin gene.

Cellular DNAs from a panel of 20 unrelated individuals were screened for restriction fragment length polymorphisms (RFLP) with a DNA probe containing the first exon of the proopiomelanocortin gene (POMC), which has been assigned to chromosome 2p23-25. Digestion with the restriction endonuclease Sst 1 revealed a high frequency RFLP. The two alleles that were found are fragments of 10- and 15-kilobase (kb) length and are in Hardy-Weinberg equilibrium with frequencies of 72.6% and 27.4%, respectively. Informative families were tested for linkage between POMC/Sst 1 RFLP and other polymorphic markers of chromosome 2. Linkage was excluded to AcP-1 (2p23-25) at 15% recombination, which is still consistent with the chromosomal assignments for these genes. The close physical linkage (10 kb) of the polymorphic locus to the POMC gene makes this RFLP a suitable marker for future linkage studies involving the POMC gene.

Chromosome Mapping↗
PubMed1981

Cloning and analysis of strong promoters is made possible by the downstream placement of a RNA termination signal.

Downstream placement of a strong transcriptional termination signal has made possible the cloning of bacteriophage T5 promoters known to exhibit high signal strength. The cloning system constructed contains two easily assayable indicator functions whose expression is controlled by the integration of promoters and terminators, respectively. By assessing transcription within the indicator regions, the efficiency of promoters as well as termination signals can be determined in vitro and in vivo.

Base Sequence↗
PubMed1981

Constituents of lymph from the non-secreting stomach of the dog.

Gastric lymph collected from the non-secreting stomach of anesthetized dogs contained glucose, Na+, K+ and creatine phosphokinase in concentrations that were similar to those in arterial and gastric venous plasma. Gastric lymph contained greater concentrations of pyruvate and lactate than in either arterial or gastric venous blood. Gastric lymph contained a high concentration of total protein similar to that in simultaneously collected hepatic lymph. Gastric lymph was collected before and after the pylorus was ligated and the stomach distended with air. These procedures were used in another study in which total protein in gastric lymph was reported to be much lower than found in the present study. The lymph to plasma ratio for protein was decreased from 0.85 +/- .04 to 0.69 +/- .04. Pyloric ligation alone caused no change in lymph protein concentration.

Animals↗
PubMed1980

Structure and genomic organization of the mouse dihydrofolate reductase gene.

The genomic organization of the mouse dihydrofolate reductase gene has been determined by hybridization of specific cDNA sequences to restriction endonuclease-generated fragments of DNA from methotrexate-resistant S-180 cells. The dihydrofolate reductase gene contains a minimum of five intervening sequences (one in the 5' untranslated region and four in the protein-coding region) and spans a minimum of 42 kilobase pairs on the genome. Genomic sequences at the junction of the intervening sequence and mRNA-coding sequence and at the polyadenylation site have been determined. A similar organization is found in independently isolated methotrexate-resistant cell lines, in the parental sensitive cell line and in several inbred mouse strains, indicating that this organization represents that of the natural gene.

Animals↗
PubMed1980

Initiation of protein synthesis in bacteria at a translational start codon of mamalian cDNA: effects of the preceding nucleotide sequence.

Plasmids containing a mouse cDNA sequence encoding the enzyme dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3) have been used to study the efficiency of initiation of protein synthesis at an ATG (AUG) translational start codon indigenous to the eukaryotic CDNA. differences in DHFR production assayed phenotypically, enzymatically, and immunologically were correlated with the primary structure of the DNA segment that precedes the translational start codon. Our results indicate that initiation of a structurally discrete and biologically functional eukaryotic protein can occur in bacteria on a fused mRNA molecule, and that the efficiency of expression is strongly affected by: (i) the extent of homology of the translational control region with the 3'-OH end of 16S ribosomal RNA, and (ii) the distance between the protein start codon and the ribosome-binding sequence on the mRNA.

Animals↗
PubMed1980

Structural organization of human genomic DNA encoding the pro-opiomelanocortin peptide.

We have isolated a human genomic DNA segment encoding the corticotropin-beta-lipotropin precursor peptide from a fetal DNA library, using previously cloned bovine cDNA for this peptide as a probe. The human genomic DNA was studied by electron microscope heteroduplex analysis and gel blotting methods, and its nucleotide sequence was determined and compared with that of cDNA corresponding to bovine pro-opiomelanocortin mRNA. From this sequence, segments of interspecies conservation and divergence, punctuated by pairs of the basic amino acid residues lysine and arginine, were identified. No noncoding intervening sequence was observed over an 830-base-pair DNA segment extending from a position near the 5' end of the structural pro-opiomelanocortin gene through the 3' terminus of the cDNA and including sequences for the component peptide hormones corticotropin and beta-lipotropin.

Adrenocorticotropic Hormone↗
PubMed1979

Nucleotide sequence of cloned cDNA for bovine corticotropin-beta-lipotropin precursor.

The nucleotide sequence of a 1,091-base pair cloned cDNA insert encoding bovine corticotropin-beta-lipotropin precursor mRNA is reported. The corresponding amino acid sequence indicates that the precursor protein consists of repetitive units and includes a third melanotropin sequence in its cryptic portion. Pairs of lysine and arginine residues separate the component peptides of the precursor.

Adrenocorticotropic Hormone↗
PubMed1978

Phenotypic expression in E. coli of a DNA sequence coding for mouse dihydrofolate reductase.

The construction and analysis of bacterial plasmids that contain and phenotypically express a mammalian genetic sequence are described. Such plasmids specify a protein that has enzymatic properties, immunological reactivity and molecular size characteristic of the mouse dihydrofolate reductase, and render host cells resistant to the antimetabolic drug trimethoprim.

Animals↗
PubMed1978

Construction of bacterial plasmids that contain the nucleotide sequence for bovine corticotropin-beta-lipotropin precursor.

mRNA that encodes the common peptide precursor for the hormones corticotropin and beta-lipotropin was purified from the neurointermediate lobe of bovine pituitaries, and double-stranded cDNA species synthesized from this template were cloned in Escherichia coli X1776 by inserting them into the Pst I endonuclease cleavage site of the pBR322 plasmid using poly(dG)poly(dC) homopolymeric extensions. Certain of the cloned cDNA inserts contain nucleotides corresponding to the complete amino acid sequence of bovine corticotropin and a coding sequence that corresponds to at least the first portion of bovine beta-lipotropin. The nucleotide sequences coding for corticotropin and beta-lipotropin are separated on the cDNA by a 6-base-pair sequence encoding lysine and arginine, indicating that the carboxyl terminus of corticotropin is connected on the precursor peptide with the amino terminus of beta-lipotropin by these two amino acids. In addition, the cloned cDNA insert is characterized by an unusually high C+G nucleotide base content as well as by a number of DNA sequence duplications.

Adrenocorticotropic Hormone↗
PubMed1978

Construction and characterization of amplifiable multicopy DNA cloning vehicles derived from the P15A cryptic miniplasmid.

Construction and characterization of a class of multicopy plasmid cloning vehicles containing the replication system of miniplasmid P15A are described. The constructed plasmids have cleavage sites within antibiotic resistance genes for a variety of commonly employed site-specific endonucleases, permitting convenient use of the insertional inactivation procedure for the selection of clones that contain hybrid DNA molecules. Although the constructed plasmids showed DNA sequence homology with the ColE1 plasmid within the replication region, were amplifiable by chloramphenicol or spectinomycin, required DNA polymerase I for replication, and shared other replication properties with ColE1, they were nevertheless compatible with ColE1. P15A-derived plasmids were not self-transmissible and were mobilized poorly by Hfr strains; however, mobilization was complemented by the presence of a ColE1 plasmid within the same cell.

Chloramphenicol↗