Search PubMed⌕ Search

Biomedical subjects

S K Choi

Publications and source records attributed to S K Choi.

At least 55 records · Page 3Linked to original sources
PubMed2000

Physical and functional interaction between the eukaryotic orthologs of prokaryotic translation initiation factors IF1 and IF2.

To initiate protein synthesis, a ribosome with bound initiator methionyl-tRNA must be assembled at the start codon of an mRNA. This process requires the coordinated activities of three translation initiation factors (IF) in prokaryotes and at least 12 translation initiation factors in eukaryotes (eIF). The factors eIF1A and eIF5B from eukaryotes show extensive amino acid sequence similarity to the factors IF1 and IF2 from prokaryotes. By a combination of two-hybrid, coimmunoprecipitation, and in vitro binding assays eIF1A and eIF5B were found to interact directly, and the eIF1A binding site was mapped to the C-terminal region of eIF5B. This portion of eIF5B was found to be critical for growth in vivo and for translation in vitro. Overexpression of eIF1A exacerbated the slow-growth phenotype of yeast strains expressing C-terminally truncated eIF5B. These findings indicate that the physical interaction between the evolutionarily conserved factors eIF1A and eIF5B plays an important role in translation initiation, perhaps to direct or stabilize the binding of methionyl-tRNA to the ribosomal P site.

Bacterial Proteins↗
PubMed2000

A case of epidermoid cyst of the intrapancreatic accessory spleen.

A 54-year-old woman presented with a huge palpable mass on left upper quadrant of the abdomen. After preoperative work-up, a cystic disease of pancreatic tail or accessory spleen was initially suspected. We performed exploratory laparotomy and resected both the spleen and a 15 x 11 cm-sized huge cystic mass containing a part of solid component which extended continuously to the pancreatic tail. The solid component, comprising the upper portion of the resected cyst, was reddish brown and granular like as normal splenic tissue. The inner surface of the cyst was smooth and was filled with yellowish white material. Histologic examination showed an epidermoid cyst originating in the accessory spleen of the pancreatic tail lacking hair or skin appendages.

Epidermal Cyst↗
PubMed2000

Prognostic significance of E-cadherin/catenin complex expression in gastric cancer.

Abnormal expression of E-cadherin/catenin complex in cancer has been associated with poor differentiation and acquisition of invasiveness, suggesting a possible role of this protein as an invasion suppressor. In this study, we conducted an immunohistochemical investigation of all components of the E-cadherin/catenin complex in 65 gastric cancer patients. Abnormal expression of E-cadherin and, alpha- and gamma-catenin occurred more frequently in diffuse than in intestinal type of gastric cancer, and correlated with poor differentiation. Abnormal expression of E-cadherin and beta-catenin correlated with poor survival. Abnormal expression of all four components of the complex was associated with poorly differentiated and diffuse-type carcinoma, and poor survival. In the multivariate analysis, abnormal expression of the E-cadherin/catenin complex was not an independent prognostic factor. These results suggest that the E-cadherin/catenin complex may be a useful marker of differentiation and prognosis in gastric cancer. Further studies are warranted to clarify the impact of the E-cadherin/catenin complex on prognostic factor of gastric cancer.

Adult↗
PubMed2000

Inflammatory pseudotumor of the urinary bladder in a child.

The inflammatory pseudotumor of the urinary bladder is rare, especially in children. It is a benign proliferative lesion of the submucosal stroma easily mistaken for a sarcoma clinically, so it should be differentiated from a malignant neoplasm. We report the case of bladder inflammatory pseudotumor in a 7-year-old girl.

Child↗
PubMed2000

Expression of tissue inhibitors of metalloproteinases (TIMPs) in hepatocellular carcinoma.

BACKGROUND: Matrix metalloproteinases (MMPs) have been implicated in the remodelling of extracellular matrix (ECM), including basement membrane. ECM remodelling is associated with pathological processes, including hepatic fibrosis, tumor invasion and metastasis. Tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2 were known to inhibit MMP-9 and MMP-2, respectively. In the present study, we examined the expression of TIMP-1 and TIMP-2 in surgical specimen pairs of hepatocellular carcinoma and nontumoral liver and the correlation between their expression and clinicopathological characteristics. METHODS: The localization of both transcripts and protein of TIMP-1 and TIMP-2 was studied by using in situ hybridization and immunohistochemistry. RESULTS: TIMP-1 and TIMP-2 mRNA transcripts were found in tumor cells, hepatocyte, sinusoidal cells, endothelial cells and stromal cells. Signal intensity of TIMP-1 was stronger than that of TIMP-2. The results of immunohistochemical stainings were concordant with those obtained by in situ hybridization. Expression of TIMP-1 and TIMP-2 was observed in tumorous tissue, in nontumorous tissue and in the portions of the tumors adjacent to the capsules. However, a clear difference in TIMP-1 and TIMP-2 mRNA expression was not observed among the three tissue types. The intensity of TIMP-2 expression was generally weaker than that of TIMP-1, and the intensity of TIMP-1 and TIMP-2 mRNA expression did not correlate with variable clinicopathological characteristics. CONCLUSION: TIMPs was expressed in tumor cells and many cell types of the nontumoral liver. Further investigations for TIMPs' unknown functional role are needed.

Adult↗
PubMed2000

Clinical results of the transjugular intrahepatic portosystemic shunt (TIPS) for the treatment of variceal bleeding.

BACKGROUND: Transjugular intrahepatic portosystemic shunt (TIPS) has been popularized for the treatment of refractory variceal bleeding. The aim of this study was to assess the safety and long-term effect of TIPS in the treatment of variceal bleeding that is not controlled with pharmacological and endoscopic treatment. METHODS: Thirty-six patients who underwent transjugular intrahepatic portosystemic shunt (TIPS) due to refractory variceal bleeding were included in the study. The effectiveness of portal decompression and bleeding control was evaluated. Upper gastrointestinal endoscopy was performed to analyse the degree of varices and portal hypertensive gastropathy (PHG) before TIPS procedure and one to three weeks after TIPS. Angiography was performed in surviving patients, if bleeding recurred, or if ultrasonography or endoscopy suggested stent dysfunction. RESULTS: TIPS were successfully placed in 36 of 38 patients (94.6%). TIPS achieved hemostasis of variceal bleeding in 34 patients (94.4%). Portal venous pressure decreased from an initial average of 28.7 +/- 7.9 to 23.2 +/- 9.4 mmHg after TIPS (p < 0.05). The portosystemic pressure gradient was significantly decreased from 15.5 +/- 6.3 to 7.8 +/- 4.1 mmHg (p < 0.01). The degree of esophagogastric varices and PHG was significantly improved after TIPS. The total length of follow-up was from one day to 54 months (mean: 355 days). The actuarial probability of survival was 83% at one year and 74% at two years. Overall, 16 episodes of stent dysfunction were diagnosed during follow-up. Stent revision by means of angioplasty was successfully performed in 14 of these episodes. CONCLUSION: TIPS is an effective and reliable nonoperative means of lowering portal pressure. This procedure has proved useful in the management of acute variceal bleeding refractory to endoscopic treatment. Surveillance by ultrasonography, endoscopy, and angiographic intervention is useful for the maintenance of shunt patency.

Adult↗
PubMed1999

Universal conservation in translation initiation revealed by human and archaeal homologs of bacterial translation initiation factor IF2.

Binding of initiator methionyl-tRNA to ribosomes is catalyzed in prokaryotes by initiation factor (IF) IF2 and in eukaryotes by eIF2. The discovery of both IF2 and eIF2 homologs in yeast and archaea suggested that these microbes possess an evolutionarily intermediate protein synthesis apparatus. We describe the identification of a human IF2 homolog, and we demonstrate by using in vivo and in vitro assays that human IF2 functions as a translation factor. In addition, we show that archaea IF2 can substitute for its yeast homolog both in vivo and in vitro. We propose a universally conserved function for IF2 in facilitating the proper binding of initiator methionyl-tRNA to the ribosomal P site.

Amino Acid Sequence↗
PubMed1999

Retroactive DNA analysis for sex determination and dystrophin gene by polymerase chain reaction with archived cytogenetic slides.

We describe a rapid and efficient diagnostic method for sex determination and the dystrophin gene by the polymerase chain reaction (PCR) using archived cytogenetic slides. Archived cytogenetic slides stored for about 4 years at room temperature were used. To confirm whether DNA analysis is possible using the archived cytogenetic slides, we extracted the DNA from the slides and amplified the Y centromeric region (DYZ3), the X centromeric region (DXZ1) and the exon 46 of the dystrophin gene. Of the 50 cases, 24 were peripheral bloods, 13 were amniotic fluid cells, 5 were chorionic villus samplings and 8 were cord bloods. The PCR related sex determination in 22 females and 28 males, showed 100% concordance with the results of chromosome analysis, and all cases showed positive band for the exon 46 of the dystrophin gene. Of the 50 cases of the archived cytogenetic slides, we were fortunate enough to obtain the fresh blood sample from one fetus whose karyotype showed 45,X[34]/46,X,+mar[145] to compare the results of the gDNA with that from archived cytogenetic slide. To confirm whether the marker chromosome was derived from Y chromosome, we studied the six loci (PABY, SRY, RPS4Y (SY16, 17), ZFY, DYS14) on the short arm, one locus (DYZ3) on the centromere and one locus (DYZ1) on the long arm. Of the 8 loci studies, all PCR related Y chromosome showed positive band from both gDNA obtained from cord blood and archived cytogenetic slides. We could conclude from the above results that the marker chromosome was derived from the Y chromosome. We believe our experiment is rapid and efficient for studies of over 10 independent loci from a single slide which has been kept in storage for up to 4 years and that archival Giemsa-stained cytogenetic slide repositories represent valuable DNA resources for clinical and forensic studies.

DNA↗
PubMed1999

RT-PCR detection and identification of three species of cucumoviruses with a genus-specific single pair of primers.

Reverse transcription and polymerase chain reaction (RT-PCR) was used for detection and identification of three cucumoviruses (cucumber mosaic virus, CMV; peanut stunt virus, PSV; tomato aspermy virus, TAV) in various plants sources with a single pair of primers, designed as CPTALL-3 and CPTALL-5. The pair of cucumovirus genus-specific primers that flank the coat protein gene were designed and used to amplify a DNA fragment of approximately ranging from 938 to 966 bp. The RT-PCR with the set of primers specifically amplified the target size of DNA fragment in all the tested cucumoviruses (CMV S-IA, S-IB and S-II, PSV and TAV). No DNA product of any length was produced when brome mosaic virus or tobacco mosaic virus RNA was used as templates. The cucumoviruses examined were differentiated by PCR-restriction fragment length polymorphism with different enzymes. This indicates that the designed primers are only specific for the cucumoviruses and useful for reliable information of identification of members of the Cucumovirus genus.

Base Sequence↗
PubMed1999

Regulation of the Bacillus subtilis phosphotransacetylase gene.

The enzyme, phosphotransacetylase (Pta), catalyzes the conversion of acetyl coenzyme A to acetyl phosphate. The putative pta gene of Bacillus subtilis, which had been sequenced as part of the Genome Project, was cloned and overexpressed in Escherichia coli. We confirmed that the gene encodes Pta by measuring the enzymatic activity of the purified protein. Insertional mutagenesis of the pta gene resulted in complete loss of the Pta activity, indicating that B. subtilis contains only one kind of pta gene. Expression of a pta-lacZ fusion was induced in the presence of excess glucose in the growth medium, and the intact ccpA gene was required for this activation. The transcriptional start site of the pta gene was located at 37 nucleotides upstream of the pta start codon, and a cre (catabolite responsive element) sequence, a cis-acting element that is responsible for the catabolite repression of a number of carbon utilization genes in B. subtilis, was identified upstream of the tentative promoter site. Experiments involving oligonucleotide-directed mutagenesis showed that the cre sequence is involved in glucose-mediated transcriptional activation.

Acetates↗
PubMed1999

Pathological difference between retractile and cryptorchid testes.

PURPOSE: We compared testicular biopsies from retractile and cryptorchid testes to determine the histological effect of testicular retraction and the necessity of treatment for retractile testes. MATERIALS AND METHODS: A total of 61 testicular biopsies were performed during orchiopexy in 36 boys 1.3 to 9.8 years old (mean age 5.4) with retractile testes (unilateral in 11, bilateral in 50) and 115 testicular biopsies were done in 83 patients with cryptorchidism (unilateral in 51, bilateral in 64) 0.5 to 14.9 years old (mean age 3.7). Parameters for germ and Sertoli cells were determined in each group. RESULTS: Mean average spermatogonial number (S/T value) and Sertoli cell index were statistically different between retractile and cryptorchid testes with values of 2.96+/-1.33 versus 0.61+/-0.87 and 26.81+/-6.75 versus 23.04+/-5.85, respectively. Average tubular degeneration phase V to VII ratio was 0.23+/-0.18 for retractile testes and 0.22+/-0.17 for cryptorchid testes which was not statistically different. CONCLUSIONS: Similar tubular degeneration phase V to VII values between retractile and cryptorchid testes indicate histological change in retractile testes and suggest the need for hormonal or surgical therapy for those patients with retractile testes lacking spontaneous descent.

Biopsy↗
PubMed1999

Morphometric aspects of extraforaminal lumbar nerve roots.

OBJECTIVE: In the posterolateral extraforaminal and anterolateral retroperitoneal approaches to lumbar spinal lesions, the neural structures in the lumbar extraforaminal region are unfamiliar to many spinal surgeons. The purpose of this study was to determine the normal anatomic morphometric parameters for all lumbar nerve roots around their exits, from the intervertebral foramen to the surrounding bony structure. METHODS: A total of 15 adult fixed cadavers were studied. The extraforaminal course of the lumbar nerve roots and the forming plexus were measured segmentally, using standard calipers, and we selected the shortest distance from the bony landmarks to the nerve roots in the horizontal plane. The bony landmarks were the most medial superior border of the transverse process (TP), the most medial inferior border of the TP, the tip of the superior articular process, and the most dorsolateral margin of the intervertebral disc space. In addition, the angle of each root exiting from the intervertebral foramen was measured using a goniometer. RESULTS: The mean distance from the medial superior border of the TP to the upper segment of the nerve root was 5.1 to 6.4 mm at L2-L5. The mean distance from the medial inferior border of the TP to the corresponding nerve root was 8.5 mm at L2 and L3 and 6 mm at L4 and L5. The mean distance from the tip of the superior articular process to the most dorsal border of the descending nerve trunk was 19 mm at L2 and L3 and 22 mm at L4 and L5. The main lumbar nerve trunk was located close to the most dorsolateral surface of the vertebral body and the intervertebral disc space, and it was topographically arranged dorsoventrally from the L5 to L2 nerve components. The average widths of the nerve trunk were 10, 14, and 25 mm at L3-L4, L4-L5, and L5-S1, respectively. The mean angles of the exiting roots in the extraforaminal region were 16 degrees at L2 and L3 and 25 degrees at L4 and L5. CONCLUSION: The lumbar nerve component, including both the lumbar trunk and each exiting nerve root in the extraforaminal region (the so-called "danger zone"), was located anteriorly at a distance more than 5 mm from the TP, more than 19 mm from the superior articular process, and up to 25 mm from the intervertebral disc space. Based on our results, the danger zone occupied up to 25 mm forward from the intervertebral foramen at the lower lumbar segments. Therefore, during operations such as percutaneous posterolateral procedures and open posterolateral or anterolateral approaches, great care should be taken within 25 mm of the extraforaminal region, especially for the lower lumbar spine.

Aged↗
PubMed1999

Cloning and sequence analysis of a new cellulase gene encoding CelK, a major cellulosome component of Clostridium thermocellum: evidence for gene duplication and recombination.

The cellulolytic and hemicellulolytic complex of Clostridium thermocellum, termed cellulosome, consists of up to 26 polypeptides, of which at least 17 have been sequenced. They include 12 cellulases, 3 xylanases, 1 lichenase, and CipA, a scaffolding polypeptide. We report here a new cellulase gene, celK, coding for CelK, a 98-kDa major component of the cellulosome. The gene has an open reading frame (ORF) of 2,685 nucleotides coding for a polypeptide of 895 amino acid residues with a calculated mass of 100,552 Da. A signal peptide of 27 amino acid residues is cut off during secretion, resulting in a mature enzyme of 97,572 Da. The nucleotide sequence is highly similar to that of cbhA (V. V. Zverlov et al., J. Bacteriol. 180:3091-3099, 1998), having an ORF of 3,690 bp coding for the 1,230-amino-acid-residue CbhA of the same bacterium. Homologous regions of the two genes are 86.5 and 84.3% identical without deletion or insertion on the nucleotide and amino acid levels, respectively. Both have domain structures consisting of a signal peptide, a family IV cellulose binding domain (CBD), a family 9 glycosyl hydrolase domain, and a dockerin domain. A striking distinction between the two polypeptides is that there is a 330-amino-acid insertion in CbhA between the catalytic domain and the dockerin domain containing a fibronectin type 3-like domain and family III CBD. This insertion, missing in CelK, is responsible for the size difference between CelK and CbhA. Upstream and downstream flanking sequences of the two genes show no homology. The data indicate that celK and cbhA in the genome of C. thermocellum have evolved through gene duplication and recombination of domain coding sequences. celK without a dockerin domain was expressed in Escherichia coli and purified. The enzyme had pH and temperature optima at 6.0 and 65 degrees C, respectively. It hydrolyzed p-nitrophenyl-beta-D-cellobioside with a Km and a Vmax of 1.67 microM and 15.1 U/mg, respectively. Cellobiose was a strong inhibitor of CelK activity, with a Ki of 0.29 mM. The enzyme was thermostable, after 200 h of incubation at 60 degrees C, 97% of the original activity remained. Properties of the enzyme indicated that it is a cellobiohydrolase.

Amino Acid Sequence↗
PubMed1998

Changes of nuclear glycoproteins in normal and simian virus 40-transformed WI-38 human lung fibroblasts.

To investigate changes in nuclear glycoproteins after transformation, nuclei and nuclear extracts were prepared from the normal and SV40-transformed WI-38 human lung fibroblasts grown in vitro. The nuclei of the normal and transformed cells were isolated by a vigorous pipetting method, and the isolated nuclei were verified by morphological and biochemical examinations. The nuclear glycocomponents, which were labelled with fluorescein isothiocyanate-lectins, were evenly found all through the isolated nuclei. Lectin blotting analysis showed that dozens of nuclear proteins contain both Man and GlcNAc moieties. The glycoproteins bearing the terminal N-acetylglucosamine sugar moieties were also demonstrated by in vitro galactosylation with [3H]-galactose. The result showed that nine glycoproteins specifically appeared or disappeared upon viral transformation or as SV40 replication products, indicating that there are significant differences in nuclear glycoproteins between the normal and SV40-transformed cells. These results suggest that the modification of Man and GlcNAc moieties are dynamic changes.

Cell Line↗
PubMed1998

Early expression of a malignant phenotype of familial hypertrophic cardiomyopathy associated with a Gly716Arg myosin heavy chain mutation in a Korean family.

The clinical course and prognosis of familial hypertrophic cardiomyopathy (HCM) are different according to the type of mutation in the genes for sarcomere proteins. It has been disputed that a mutation, which occurs at a functionally important region in the sarcomere proteins, may increase the penetrance and expressivity of the disease. We searched for a causative mutation in an HCM family, which is characterized by early expression of clinical phenotype, high incidence of sudden death at young ages, and progressive heart failure in adults. Among the 32 family members in 4 generations, 13 were affected; 4 died suddenly before age 16, 2 children have already had full expression of the cardiac hypertrophy, and other adults have either progressive heart failure or poor left ventricular systolic functions. PCR-SSCP (polymerase chain reaction-single strand confirmation polymorphism) analysis of genomic DNAs isolated from peripheral blood leukocytes of the family members identified a Gly716Arg mutation in the cardiac beta-myosin heavy chain gene, which was cosegregated with the clinical phenotype. The mutation is localized near a functionally important site of the myosin heavy chain, the 2 active thiols, which contribute to the adenosine triphosphatase activity of myosin S1. This family provides further evidence that the mutation, which occurs at a functionally important site of the myosin heavy chain, is associated with the high penetrance and early expression of HCM.

Adolescent↗
PubMed1998

Sequence analysis of the Bacillus subtilis 168 chromosome region between the sspC and odhA loci (184 degrees-180 degrees).

The nucleotide sequence of 45,389 bp in the 184 degrees-180 degrees region of the Bacillus subtilis chromosome, containing the cge cluster, which is controlled by the sporulation regulatory protein GerE, was determined. Fifty-four putative ORFs with putative ribosome-binding sites were recognized. Seven of them correspond to previously characterized genes: cgeB, cgeA, cgeC, cgeD, cgeE, ctpA, and odhA. The deduced products of 25 ORFs were found to display significant similarities to proteins in the data banks. We have identified genes involved in detoxification, cell walls, and in the metabolism of biotins, purines, fatty acids, carbohydrates and amino acids. The remaining 22 ORFs showed no similarity to known proteins. Both an attachment site of the SPbeta prophage and 2 new putative DNA replication terminators were identified in this region.

Bacillus subtilis↗
PubMed1998

Promotion of met-tRNAiMet binding to ribosomes by yIF2, a bacterial IF2 homolog in yeast.

Delivery of the initiator methionine transfer RNA (Met-tRNAiMet) to the ribosome is a key step in the initiation of protein synthesis. Previous results have indicated that this step is catalyzed by the structurally dissimilar translation factors in prokaryotes and eukaryotes-initiation factor 2 (IF2) and eukaryotic initiation factor 2 (eIF2), respectively. A bacterial IF2 homolog has been identified in both eukaryotes and archaea. By using a combination of molecular genetic and biochemical studies, the Saccharomyces cerevisiae IF2 homolog is shown to function in general translation initiation by promoting Met-tRNAiMet binding to ribosomes. Thus, the mechanism of protein synthesis in eukaryotes and prokaryotes is more similar than was previously realized.

Codon, Initiator↗