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Biomedical subjects

E C Choi

Publications and source records attributed to E C Choi.

53 records · Page 3Linked to original sources
PubMed1993

A macrolide-lincosamide-streptogramin B resistance determinant from Bacillus anthracis 590: cloning and expression of ermJ.

The inducible macrolide-lincosamide-streptogramin B resistance determinant, ermJ, from Bacillus anthracis 590 was cloned in Escherichia coli CSH26. The DNA sequence of ermJ was similar to that of ermK or ermD from B. licheniformis, suggesting that ermK-like genes have been distributed in Bacillus strains by transposition. Expression of ermJ was achieved in a B. subtilis minicell system, and the rRNA methyltransferase product of ermJ was purified. The molecular mass of the enzyme was 58 kDa, and it was concluded to be a homodimer. Its biochemical characteristics were different from those of ermC methyltransferase.

Amino Acid Sequence↗
PubMed1991

Transcriptional attenuation control of ermK, a macrolide-lincosamide-streptogramin B resistance determinant from Bacillus licheniformis.

ermK instructs bacteria to synthesize an erythromycin-inducible 23S rRNA methylase that confers resistance to the macrolide, lincosamide, and streptogramin B antibiotics. Expression of ermK is regulated by transcriptional attenuation, in contrast to other inducible erm genes, previously described, which are regulated translationally. The ermK mRNA leader sequence has a total length of 357 nucleotides and encodes a 14-amino-acid leader peptide together with its ribosome binding site. Additionally, the mRNA leader sequence can fold in either of two mutually exclusive conformations, one of which is postulated to form in the absence of induction and to contain two rho factor-independent terminators. Truncated transcription products ca. 210 and 333 nucleotides long were synthesized in the absence of induction, both in vivo and in vitro, as predicted by the transcriptional attenuation model; run-off transcription in vitro with rITP favored the synthesis of the full-length run-off transcript over that of the 210- and 333-nucleotide truncated products. Northern (RNA) blot analysis of transcripts synthesized in vivo in the absence of erythromycin indicated that transcription terminated at either of the two inverted complementary repeat sequences in the leader that were postulated to serve as rho factor-independent terminators; moreover, no full-length transcripts were detectable in the uninduced samples. In contrast, full-length (ca. 1,200-nucleotide) transcripts were only detected in RNA samples synthesized in vivo in the presence of erythromycin. Full-length transcripts formed in the absence of induction from transcriptional readthrough past the two proposed transcription terminators would fold in a way that would sequester the ribosome binding site together with the first two codons of the ErmK methylase, reducing its efficiency in translation. This feature could therefore provide additional control of expression in the absence of induction; however, such regulation, if operative, would act only secondarily, both in time and place, relative to transcriptional control. Analysis by reverse transcriptase mapping of in vivo transcripts from two primers that bracket the transcription terminator responsible for the 210-nucleotide truncated fragment supports the transcriptional attenuation model proposed and suggests further that the synthesis of the ermK message is initiated constitutively upstream of the proposed terminator but completed inductively downstream of this site.

Amino Acid Sequence↗
PubMed1990

Immunoaffinity purification of hepatitis B surface antigen using anti-idiotype as a specific eluent.

An immunoaffinity method for the purification of hepatitis B surface antigen (HBsAg) using monoclonal anti-idiotype (anti-Id) as a specific eluent is described. Ammonium sulfate fractions of HBsAg-containing plasma were absorbed on monoclonal idiotype (Id) immunoadsorbents. The bound material was eluted from the column with the anti-Id of HBsAg. The eluate containing anti-Id was further purified by gel filtration. The procedure yielded highly purified HBsAg. The final HBsAg product was free from contaminating human plasma and mouse ascites proteins. The procedure is generally applicable and particularly attractive when the antigen is unstable under commonly used elution conditions.

Antibodies, Anti-Idiotypic↗
PubMed1989

Inhibition ELISA for hepatitis B surface antigen (HBsAg) using monoclonal idiotype-anti-idiotype interaction.

Monoclonal anti-idiotypic antibody (Anti-Id) to the common (a) epitope of hepatitis B surface antigen (HBsAg) were raised and used to detect serum HBsAg in an inhibition enzyme-linked immunosorbent assay (inhibition ELISA). HRP-labelled Id 8D-3-6 was reacted with Anti-Id 4-8H coated on the solid phase in the presence of HBsAg. The ability of the antigen to inhibit the binding of labelled Id 8D-3-6 to anti-Id 4-8H was determined and the results correlated well with those obtained by radioimmunoassay. This assay requires only one washing step, takes 2 h and covers the range 10 ng/ml to 1 microgram HBsAg/ml. The inhibition ELISA is a more convenient, rapid and relatively sensitive assay which can be used to measure the level of a wide range of serum HBsAg.

Animals↗
PubMed1989

Primary carcinoid tumor of the larynx.

A case of laryngeal carcinoid in a 54-year-old Korean female is reported and discussed. This tumor is extremely rare in the larynx and there have been just over twenty cases reported in the literature to date. The case showed an initial histologic finding of epithelial dysplasia and was finally confirmed to be a carcinoid tumor. Laryngeal carcinoids are often atypical histologically and may be misdiagnosed as undifferentiated carcinoma. An electron microscopic study revealed neurosecretory-type granules. Although the patient underwent a total laryngectomy and radical neck dissection, multiple hepatic metastasis was noted postoperatively.

Carcinoid Tumor↗
PubMed1982

Inhibition of DNA synthesis in murine tumor cells by geldanamycin, an antibiotic of the benzoquinoid ansamycin group.

The mechanism of action of geldanamycin, a benzoquinoid ansamycin, was investigated with murine lymphoblastoma L5178Y cells. The agent inhibited the cell growth at concentrations over 0.01 micrograms/ml. The antibiotic blocked DNA synthesis more markedly than RNA and protein syntheses. Mitosis was not significantly affected by the drug in the cells synchronized with demecolcine (Colcemid). The antibiotic did not interfere with in vitro assembly of tubulin. In the synchronized cells, strong inhibition of DNA synthesis was observed when geldanamycin was introduced into the culture prior to S phase of the cell cycle. The degree of inhibition was stronger with prolongation of incubation period and with increase of DNA synthesis rate. The results suggested that initiation of DNA synthesis or S phase is affected by the drug. DNA degradation was not significantly induced in vivo by the antibiotic. Geldanamycin blocked DNA polymerase alpha more markedly than beta and gamma. The degree of inhibition depended up on concentrations of enzyme but not upon those of template, suggesting a drug-enzyme interaction. IC50 for DNA polymerase alpha was 10 micrograms/ml and for DNA polymerase beta 100 micrograms/ml at low concentrations of enzyme. The inhibition of DNA polymerase alpha by the antibiotic was non-competitive and Ki was 20 microM.

Animals↗
PubMed1980

In vivo and in vitro cross-resistance of kanamycin-resistant mutants of E. coli to other aminoglycoside antibiotics.

Cross resistance of kanamycin-resistant mutants of E. coli Q13 to other aminoglycosides (streptomycin, neomycin, gentamicin and dibekacin) was demonstrated in vivo (growth) and in vitro (polyphenylalanine synthesis, codon misreading and translocation on the ribosomes). Kanamycin-resistant mutants, R1-4, R2-1, R2-2, R3-3 and R3-5 showed various degrees of cross-resistance to streptomycin, gentamicin, neomycin and dibekacin in vivo. In vitro, polyphenylalanine synthesis was more resistant to kanamycin, streptomycin, neomycin and gentamicin on the ribosomes of the kanamycin-resistant mutants than on those of the parental strain. In the presence of kanamycin, neomycin or gentamicin, less degrees of [14C]isoleucine uptake with poly[U] (codon misreading) were observed on the ribosomes obtained from the resistant mutants than on the sensitive cell ribosomes. The N-acetyl-[14C]phenylalanyl-puromycin synthesis enhanced by an elongation factor, EF-G and GTP (translocation) was more resistant to kanamycin and dibekacin on the mutant ribosomes than on the parental ribosomes. The results indicate that the cross-resistance to other aminoglycoside antibiotics, as well as the kanamycin resistance, are attributed to mutational alterations of the ribosomes in these mutants.

Aminoglycosides↗
PubMedDate not supplied

Clinical significance of neck node metastasis in squamous cell carcinoma of the maxillary antrum.

PURPOSE: To further clarify the clinical significance of neck node metastasis in squamous cell carcinoma of the maxillary sinus (maxillary SCC). MATERIALS AND METHODS: The medical charts of the 116 patients with maxillary SCC were retrospectively reviewed. Twelve patients (10.3%) presented initially with neck node metastases, and 14 (13.5%) of 104 node-negative patients subsequently developed regional recurrence during the follow-up period. The high-risk factors for neck node metastasis, patterns of regional failure, and survival for node-positive patients were analyzed with the patient cohort that had largely been treated with radiation alone. RESULTS: Of the various factors, the tumor extension to the nasopharynx or oral cavity was the statistically significant determinants predictive of neck node metastasis at the initial diagnosis. During the follow-up period, regional failure was far less common than local failure (19.0% v 68.1%), and the majority of regional failures were accompanied by local recurrences. The oral cavity extension and control status of local disease were the high-risk factors for subsequent development of regional recurrence in node-negative patients. The overall 5-year survival rate for node-positive patients (16.7%) showed a poorer outcome compared with that for node-negative patients (31.3%), but it was similar to that of T4N0 patients (26.6%). Although patients who subsequently developed neck node recurrence during follow-up represented a dismal prognosis, uncontrolled local diseases in these patients still remained a major problem, resulting in a poor prognosis. CONCLUSIONS: Despite an unfavorable prognosis of patients with neck node metastasis, an aggressive trial to achieve maximum local control of the primary tumor was considered to be more important than elective neck treatments.

Adult↗
PubMedDate not supplied

Primary squamous cell carcinoma of the parotid gland.

PURPOSE: To investigate the clinical behavior and treatment outcome of patients with primary squamous cell carcinoma (SCC) of the parotid gland. PATIENTS AND METHODS: Twelve cases of primary SCC originating in the parotid gland were retrospectively reviewed. The majority of patients had a locally advanced disease. Eight cases underwent a combination of radical surgery and postoperative radiotherapy, whereas the remaining four cases were treated with radiotherapy alone. Patterns of treatment failure, survival rate, and prognostic factors for these patients were investigated. RESULTS: The predominant pattern of failure was local failure, either alone or in combination with other failures. Two patients who were treated with radiation alone had persistent disease after completion of treatment, whereas 4 of 8 patients who received combined modality treatment and 2 of 4 patients who were treated with radiation alone subsequently developed local recurrences in the primary site or surgical bed. The local failure rate and regional failure rate were 58% and 25%, respectively. Most locoregional recurrences developed within 1 year after initial treatment. Only 2 patients had distant metastasis. The prognosis appeared to be relatively poor for those patients, compared with those with SCC in other head and neck sites. The overall 5-year actuarial survival rate and the disease-free survival rate were 31% and 33%, respectively. Although advanced stage, facial nerve palsy, and regional lymph node metastasis all portended an unfavorable prognosis, only patient age and treatment modality were found to be statistically significant poor prognostic factors. CONCLUSIONS: Primary SCC of the parotid gland is an uncommon tumor with a highly malignant potential. Our results indicate that a combination of radical surgery and postoperative radiotherapy is the treatment of choice for achieving better locoregional control rates and improved cure rates in the treatment of these patients.

Adult↗
PubMedDate not supplied

Unique aspects of Korean-American mothers.

A descriptive study was conducted to explore Korean beliefs and attitudes toward pregnancy, birth, and postpartum practices. In addition, overall characteristics of Korean mother-infant interactions are described. The sample consisted of 21 healthy Korean mothers and their term infants. The study revealed that Korean mothers in the United States continued Korean cultural practices related to pregnancy, birth, and postpartum behaviors. One alteration from traditional birth practices was related to infant feeding. Although many of the mothers believed that breastfeeding was better for the infants, the mothers chose to bottle-feed. Nurses need to use knowledge of the value systems of culturally different patients to plan relevant nursing care.

Attitude↗