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Biomedical subjects

Y C Choi

Publications and source records attributed to Y C Choi.

At least 55 records · Page 3Linked to original sources
PubMed1991

RETT's syndrome in Korea--report of two cases.

Rett's syndrome(RS) is a progressive neurodegenerative disorder characterized by exclusive occurrence in females, autistic behavior, dementia, gait ataxia, loss of purposeful use of the hands with stereotypic hand movement, and seizures. Initially RS was considered to be very rare; however, recent reports suggest that the prevalence is considerably higher and occurrence is world-wide. Because the pathophysiological process remains unknown, the diagnosis of RS is based mainly on its characteristic clinical features and course. We experienced two cases of RS which, to our knowledge, are the first reported in Korea. It is quite possible that many patients with RS not yet being diagnosed in Korea.

Child↗
PubMed1990

Effect of the N-terminal hydrophobic sequence of hepatitis B virus surface antigen on the folding and assembly of hybrid beta-galactosidase in Escherichia coli.

To investigate the mechanism of inclusion body formation and the effect of a hydrophobic sequence on the in vivo polypeptide folding, the aggregation caused by recombinant fusion beta-galactosidase in Escherichia coli was examined. Two plasmids were constructed: pTBG(H-) carried only the preS2 sequence of the hepatitis B virus surface antigen (HBsAg) in front of the beta-galactosidase gene (lacZ) while pTBG(H+) carried an additional sequence encoding the amino-terminal hydrophobic sequence of the S region of HBsAg between preS2 and lacZ. Unlike cells expressing the fusion protein not containing the hydrophobic sequence, E. coli JM109/pTBG(H+) exhibited temperature-sensitive production of beta-galactosidase. As the culture temperature increased the activity decreased dramatically. This decrease in activity was not due to a decrease in fusion polypeptide production, but rather the fusion polypeptides containing the hydrophobic sequence aggregated within the cells at high temperature. However once the fusion polypeptides folded into proper conformation at low temperature, they maintained the activity even at high temperature. The results indicate that aggregation is a consequence of incorrect folding and assembly of the polypeptides, and is not derived from the native structure. The aggregates of the pTBG(H+)-encoded fusion polypeptides did not revert to active form when the culture temperature was lowered.

Amino Acid Sequence↗
PubMed1990

A case of Leigh's disease with initial manifestation of dystonia.

A case of Leigh's disease (subacute necrotizing encephalomyelopathy) is reported with such noteworthy features as early onset, dystonia, paraparesis the presence of low attenuation areas in both basal ganglias on computerized tomography of the brain and the presence of a high signal intensity in both basal ganglias in T2 weighted image by MR. The electron microscopic findings of muscle biopsy are suggestive of pleoconial mitochondrial myopathy.

Basal Ganglia↗
PubMed1985

Isolation and characterization of a 125-kilodalton rapidly labeled nucleolar phosphoprotein.

A 125-kilodalton (kDa) phosphoprotein was isolated from nucleoli of Novikoff hepatoma cells in the presence of various inhibitors of proteases, alkaline phosphatase, and RNase. This protein was the most highly phosphorylated protein found thus far in the nucleolus. The half-life of [32P]phosphate in the 125-kDa phosphoprotein was approximately 60 min. Amino acid analysis of the protein showed it had a high serine content (15.5 mol %), a high glutamine plus glutamic acid content (15.5 mol %), and a high lysine content (10.3 mol %). Phosphoserine was the only phosphorylated amino acid identified. After alkaline hydrolysis of the 32P-labeled protein, ribonucleotides were found which accounted for approximately 8.5% of the [32P]phosphate. After cytidine 3',5'-[32P]diphosphate ([32P]pCp) labeling by RNA ligase, several oligoribonucleotide sequences were purified including GGGCOH and GGGGCOH. The binding of oligonucleotides to peptides was stable under denaturing fractionation conditions including 6 M urea treatment and incubation at 100 degrees C for 10 min in sodium dodecyl sulfate and beta-mercaptoethanol. Furthermore, when nucleotide-peptide complex was treated with ribonuclease T2 followed by snake venom phosphodiesterase, the junctional nucleotide pCp was released. These results suggest that one or more ribonucleotides are covalently bound to the 125-kDa phosphoprotein.

Animals↗
PubMed1985

Structural organization of ribosomal RNAs from Novikoff hepatoma. I. Characterization of fragmentation products from 40 S subunit.

The internal topography of rRNAs in situ was probed with RNase T1. Isolated polysomes were treated with RNase T1 to examine the unprotected regions of rRNAs contained in polysomes. The 40 S subunit yielded 23 cleavage products of 18 S rRNA, of which the fragments from three domains were isolated, characterized, and compared with the secondary structure of 18 S rRNA proposed by Chan et al. (Chan, Y.-L., Gutell, R., Noller, H.F., and Wool, I.G. (1984) J. Biol. Chem. 259, 224-230). There were two consistent fragments (1-71, 1-74) derived from the 5' domain, where two alternative sites were cleaved at a loop, indicating conformational flexibility of 40 S subunit. There was a fragment (1760-1874) consisting of the 3'-end portion derived from the 3'-minor domain where a single site was cleaved at a loop. These patterns of cleavages at the single-stranded regions are similar to those of bacterial 16 S rRNA. In contrast to the phylogenetic similarity of cleavages between 16 S rRNA and 18 S rRNA (Stiegler, P., Carbon, P., Zucker, M., Ebel, J. P., and Ehresmann, C. (1981) Nucleic Acids Res. 9, 2153-2172), a difference was found in one fragment (777-840) derived from the unassigned long insert of the central domain. Based on the determination of its cleavage sites, a secondary structure model is proposed, which conserves a phylogenetic consistency among yeast, Xenopus, rat, and rabbit.

Animals↗
PubMed1985

Structural organization of ribosomal RNAs from Novikoff hepatoma. II. Characterization of possible binding sites of 5 S rRNA and 5.8 S rRNA to 28 S rRNA.

Interrelationships among 5 S, 5.8 S, and 28 S rRNA were probed by methods employed in the accompanying report (Choi, Y. C. (1985) J. Biol. Chem. 260, 12769-12772). Two complexes were isolated from 20 S ribonucleoprotein (RNP) fraction and 60 S subunit. The 20 S RNP fraction was found to contain the 3'-340 nucleotide fragment (domain VII) in association with 5 S rRNA. The 60 S subunit contained a stable complex consisting of the 5'-upstream portion (4220-4462, domain VI and VII), the 3'-downstream portion (4463-4802, domain VII) of 3'-583 nucleotides fragment, and 5.8 S rRNA. By computer analysis and hybridization, the 5'-upstream portion was found to contain the 5.8 S rRNA contact site. By affinity chromatography, the 3'-downstream portion was found to contain the 5 S rRNA association site. Furthermore, by comparison with the secondary structure of 28 S rRNA proposed by Hadjiolov et al. (Hadjiolov, A. A., Georgiev, O. I., Nosikov, V. V., and Yavachev, L. P. (1984) Nucleic Acids Res. 12, 3677-3693), it was found that domain VII is capable of binding 5.8 S rRNA and 5 S rRNA juxtaposed to each other. Accordingly, a model was proposed to indicate that a possible contact site for 5.8 S rRNA is within the region surrounding the alpha-sarcin site (4333-4350) and is a possible association site of 5 S rRNA within the 3'-downstream portion (4463-4802) of the 3'-583 nucleotide fragment (4220-4802).

Animals↗
PubMed1983

Chromosome localization of highly repetitive human DNA's and amplified ribosomal DNA with restriction enzymes.

Restriction endonucleases cut and partially removed DNA throughout fixed air-dried human metaphase chromosomes. Some enzymes produced a G-banding pattern; some revealed the presence of multiple chromosome-specific classes of highly repetitive DNA in C-band heterochromatin. Enzymes that produced the informative C-band patterns had recognition sequences that were four or five, but not six, base pairs long and did not contain a cytosine-guanine doublet. In both rat and human chromosomes, regions containing amplified ribosomal RNA genes were specifically removed by the restriction endonuclease Msp I.

Chromosome Banding↗
PubMed1983

Ultrastructural and purification studies on human tumor nucleolar antigens and nucleolar particles.

The presence of common nucleolar antigens in a broad array of human malignant tumors has led to several lines of investigations. In addition to studies on an increasing number of benign and malignant neoplasms with a variety of antibodies designed to statistically evaluate the presence of nucleolar antigens, purification procedures and chemical analyses are being used to characterize the specific antigens. The localization of the nucleolar antigens in HeLa cells was studied by the postembedding immunoelectron microscopic procedure employing rabbit antibodies to nucleoli or nuclear Tris extracts of these cells. The products of the peroxidase-antiperoxidase complexes visualized by the reaction with diaminobenzidine in nucleoli were mainly found in the nucleolonemas which contain the dense nucleolar RNP components. When these nucleoli became compact after treatment of HeLa cells with adriamycin, the distribution of the immunoreactive products was altered along with distribution of the dense nucleolar components. The human nucleolar antigens were mainly localized to nucleolar regions containing the nucleolar RNP components. Improved purification of the antigens made it possible to provide a satisfactory amino acid analysis of one pI 6.3 antigen. Interestingly, some of the nucleolar antigen was found in miniparticle undescribed until now.

Amino Acids↗
PubMed1981

Experimental siderosis of articular chondrocytes cultured in vitro.

Siderosis of rabbit articular chondrocytes was produced in vitro as a model for the cartilage damage of hemophilic arthropathy. Both FeSO4 0.1-2.5 mM and rabbit hemoglobin (as hemolyzed serum, 14 mg/ml) caused iron storage in cell and organ culture. FeSO4 was far more effective. The fine structure of the siderosomes resulting from both iron sources was comparable to that observed in hemophilic and other forms of hemosiderosis. Particles resembling ferric oxyhydroxide were included in the FeSO4 but not the hemoglobin derived siderin. Iron storage following FeSO4 was enhanced 5-fold by culturing with rabbit rather than fetal calf serum. Despite repeated washing of the cultures and detachment with trypsin, an extracellular pool of Fe3+ persisted in the cell pellets. Cytotoxicity of Fe was manifested by formation of myelin bodies and a dose-dependent reduction of cell number. There was an inverse relationship between cytotoxicity and iron storage following administration of FeSO4 to five other cell types. Ascorbate 40 micrograms/ml stimulated DNA synthesis but had no protective effect against the cytotoxicity of FeSO4. Little erythrophagocytosis was showen by the chondrocytes. Desferrioxamine (0.01--2.5 mM) was markedly toxic for dividing but not for stationary chondrocytes. Administered after iron storage had been induced with FeSO4, 1.0--2.5 mM desferrioxamine removed stainable siderin granules over the course of 4 days.

Animals↗
PubMed1980

Effect of platelet lysate on growth and sulfated glycosaminoglycan synthesis in articular chondrocyte cultures.

Human platelet lysate (PL) has a strong growth promoting action on rabbit articular chondrocytes in monolayer culture. The responsible factor is heat stable (56 degrees C, 30 minutes) and above 10,000 MW. PL (80 microgram protein/ml) reduces cell protein content and sulfated glycosaminoglycan synthesis. Synthesis of DNA is stimulated within the first 12 hours of culture but the decline in radiosulfate incorporation lags. PL acts to a slight extent on chondrocytes in serum-free media, but its effect is potentiated by "platelet-poor human serum" or fetal bovine serum. PL is one of several agents having such effects on chondrocytes cultured in serum-containing media. Stimulation of growth in this cell type thus reduces nonreplicative biosynthetic activity nonspecifically. In the epiphyseal growth plate and in pathologic alterations of permeability of the matrix of articular cartilage, platelet-derived factors, together with somatomedin or other cofactors in serum, may be the principal mediator of growth of chondrocytes in vivo.

Animals↗
PubMed1980

The effect of serum on monolayer cell culture of mammalian articular chondrocytes.

Large variations were found in the ability of six species of sera to support growth of rabbit, human and dog articular chondrocytes in monolayer culture. In most instances the DNA content of the cell pellets increased directly as the serum concentration rose from 10 to 30%. Indications of inhibitory as well as growth-promoting actions were found in some sera. Stimulation of rabbit chondrocyte proliferation by increasing concentrations of serum was accompanied by a reduction of radiosulfate incorporation and cell protein content. There was no consistent relation between the response of chondrocytes from a given species and its homologous serum. However, the growth of human chondrocytes was greatly potentiated by human serum provided that interference with initial attachment of the cells to the culture flask by homologous serum was overcome by priming with fetal calf serum.

Animals↗
PubMed1979

Studies on the specificity of preribosomal RNA transcription in nucleoli after selective deproteinization.

Fidelity of preribosomal RNA transcription in vitro was studied after selective deproteinization of nucleoli using either sequential salt extraction or sodium deoxycholate treatment. Homochromatography fingerprinting and identification of marker oligonucleotides from a T1 ribonuclease digest of the transcripts were used to evaluate the RNA products. These studies indicated that: (1) nucleoli retained their endogenous RNA polymerase I activity and the specificity of transcription up to 0.6 M NaCl extraction; (2) exogenous RNA polymerase I transcribed nucleolar chromatin only after 1.0 M NaCl extraction and the transcription pattern, like that of totally deproteinized DNA, was completely random; (3) extraction of nucleoli with deoxycholate resulted in a DNP complex in which the endogenous RNA polymerase I transcribed pre-rRNA specifically; however, it also initiated random transcription, producing a "mixed" fingerprint pattern on the homochromatogram. The random transcription was selectively inhibited either by deoxycholate or rifampicin AF/013. These studies indicate that the selectivity of pre-rRNA transcription is due both to the endogenous RNA polymerase I molecules that were involved in transcription in vivo and are tightly bound to the template and to factors in intact nucleoli which prevent random transcription by the released RNA polymerase I molecules.

Animals↗
PubMed1978

Modified nucleotides in T1 RNase oligonucleotides of 18S ribosomal RNA of the Novikoff hepatoma.

The primary structure of 18S rRNA of the Novikoff hepatoma cells was investigated. Regardless of whether the primary sequence of 18S rRNA is finally determined by RNA sequencing methods or DNA sequencing methods, it is important to identify numbers and types of the modified nucleotides and accordingly the present study was designed to localize the modified regions in T1 RNase derived oligonucleotide. Modified nucleotides found in 66 different oligonucleotide sequences included 2 m62A, 1 m6A, 1 m7G, 1m1cap3psi, 7 Cm, 13 Am, 9 Gm, 11 Um, and 38 psi residues. A number of these modified nucleotides are now placed in defined sequences of T1 RNase oligonucleotides which are now being searched for in larger fragments derived from partial T1 RNase digests of 18S rRNA. Improved homochromatography fingerprinting (Choi et al. (1976) Cancer Res. 36, 4301) of T1 RNase derived oligonucleotides provided a distinctive pattern for 18S rRNA of Novikoff hepatoma ascites cells. The 116 spots obtained by homochromatography contain 176 oligonucleotide sequences.

Base Sequence↗
PubMed1978

Cytomegalovirus infection in guinea pigs. I. Viremia during acute primary and chronic persistent infection.

Studies on the pathogenesis of cytomegalovirus (CMV) infection in guinea pigs have revealed two distinct phases of infection, without any signs of clinical disease. During acute primary infection, viremia was easily demonstrated and infectious virus was recovered from various tissues, including lung, spleen, and kidney, of the infected animal two to 10 days after inoculation. Chronic persistent infection was readily established thereafter. In animals with chronic persistent infection with high levels of circulating antibody, infectious virus was consistently isolated from the salivary gland and pancreas. Evidence of CMV in the blood of the persistently infected animals was detected only occasionally and only when a highly sensitive method and/or a large inoculum was used. However, the anticoagulant heparin was found to inactivate CMV significantly during collection of blood. These data suggest that CMV was indeed circulating in the blood of apparently health but persistently infected animals for prolonged periods. Such infected blood could conceivably be the source of CMV infection when large quantities of blood are given to susceptible recipients.

Acute Disease↗