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Biomedical subjects

K B Choo

Publications and source records attributed to K B Choo.

71 records · Page 4Linked to original sources
PubMed1988

Molecular analysis of hemoglobin H disease in Taiwan.

The molecular basis of seven Chinese patients in Taiwan with hemoglobin H disease was investigated and was found to be heterogeneous in the mutation type. They were alpha-thalassemia-1 mutation combined with hemoglobin Constant Spring, an undetermined nondeletion form of alpha-thalassemia and a deletion form of alpha-thalassemia-2 mutations. The alpha-thalassemia-1 mutation was shown to be the --SEA type I haplotype.

Adult↗
PubMed1987

Presence of episomal and integrated human papillomavirus DNA sequences in cervical carcinoma.

Thirty surgical samples of squamous cell carcinoma of the cervix obtained from Chinese women were analysed for the presence of human papillomavirus (HPV) types 16 and 18 using Southern blot hybridization procedure. HPV16 was detected in 53% while HPV18 was found in only 6% of the samples analyzed. When compared with other reports, variation in the geographic distribution of these two HPV types in association with cervical carcinoma is noted. Thirty-seven and a half percent of the HPV16-positive samples contained this HPV type in episomal form and an equal number in cellular DNA-integrated form. The simultaneous presence of both episomal and integrated forms was found in the remaining 25% of the positive samples. The two HPV18-positive cases harbored only episomal viral genome and were not superinfected by HPV16. Analysis of the HPV16 integration samples showed that single integration events had probably occurred and some of the viral sequences had been lost on or subsequent to integration.

Carcinoma, Squamous Cell↗
PubMed1987

Hepatitis B virus infection of cord blood leukocytes.

The presence of hepatitis B virus (HBV) DNA in the serum and leukocytes obtained from the peripheral blood of 24 mothers and from the cord blood of their newborns was determined by hybridization procedures. HBV DNA was not detected in the serum and leukocytes of six HBsAg-, HBeAg-negative and two HBsAg-positive, HBeAg-negative mothers and their newborn infants. Among the 16 HBsAg-positive carrier mothers, HBV DNA was found in 13 cases (81%) in the serum and in two cases (12%) in leukocytes. Though the viral DNA was not present in sera, it was detected in two of the 16 cord blood leukocyte samples. In follow-up studies, these two infants did not seroconvert up to 15 months of age and they became carriers with elevated serum alanine aminotransferase levels. The results suggest that HBV may be transmitted vertically and such in utero infection may have resulted in immune tolerance leading to a carrier state.

Alanine Transaminase↗
PubMed1987

Integration of human papillomavirus type 16 into cellular DNA of cervical carcinoma: preferential deletion of the E2 gene and invariable retention of the long control region and the E6/E7 open reading frames.

The integration patterns of human papillomavirus (HPV) type 16 in the cellular DNA of six cervical carcinoma samples were analyzed by the Southern blot procedure. None of the HPV integrants retained the entire viral genome. Double HPV integration was found in one case while all other cases were single integrants. In some samples, internal deletion and selective amplification of the viral sequences were observed. On integration, the E2 open reading frame (ORF) was invariably lost but the E6/E7 ORFs and the long control region of the HPV-16 genome were retained in all seven integrations analyzed and may play a role in cellular transformation and/or maintenance of the transformed phenotype.

Base Sequence↗
PubMed1986

Effect of vector type, host strains and transcription terminator on heterologous gene expression in yeast.

Using the surface antigen gene of the hepatitis B virus, and the promoter and terminator sequences of the yeast pho5 gene as a model system, a series of closely related expression plasmids were constructed to investigate the effect of vector type, genetic background of host strains and the presence of transcription terminator on the expression of heterologous gene in yeast. Plasmids carrying the replication origin of the 2 mu plasmids were found to be much more stable than those either independently or simultaneously carrying ars1 sequences. Gene expression was also higher with 2 micron-based plasmids. Yeast selection marker (trp1 or leu2) and therefore the host strains used did not have significant effects on gene expression. Addition of transcription terminator sequences downstream to the HBsAg gene also contributed only limited increases in gene expression levels.

Escherichia coli↗
PubMed1986

Analysis of six distinct integrated hepatitis B virus sequences cloned from the cellular DNA of a human hepatocellular carcinoma.

Six distinct hepatitis B virus (HBV) integrations and the flanking cellular sequences were cloned from a hepatoma DNA preparation. None of the cloned fragments retains the entire HBV sequences but the surface antigen (HBsAg) gene and the HBV enhancer are retained in three of the six clones. The other three clones carry only short and possibly highly rearranged HBV genomic sequences and seem to contain some GC-rich clusters. Members of the repetitive Alu family are also found in the vicinity of five of the six integration regions which may have contributed to genome instability. In these six clones, the preferred integration sites are shown to lie within the single-strand region of the HBV genome. None of the clones carries in the flanking cellular sequences any of the 17 oncogenes tested, although the possibility still exists that an oncogene may be found on the side of the genome which has not been cloned. This work thus paves the way for detailed sequence analysis of virus-host junctions, for transfection studies of the HBV integration events, and for a search of genes in the flanking cellular sequences which may have been activated by the retained HBV enhancer using the clones described.

Base Sequence↗
PubMed1986

Hepatitis B virus DNA in leukocytes of patients with hepatitis B virus-associated liver diseases.

In order to determine the relationship between hepatitis B virus (HBV) infection of human white blood cells and different forms of HBV-associated liver diseases, we tested for HBV DNA in the sera and leukocytes of 11 healthy individuals without any serological markers of HBV infection and 91 patients with HBV infection and other gastrointestinal and urinary diseases by dot and Southern blot hybridization. HBV DNA was found in leukocytes of chronic HBV carriers, in acute and chronic hepatitis, and in patients with liver cirrhosis and hepatocellular carcinoma. Between 27 and 50% of individuals in different categories of patients examined were positive for leukocyte HBV DNA. HBV DNA was also detected in the sera of some of these patients but was absent in others. Serum HBV DNA-positive rates seemed to be highest in hepatitis B e antigen-positive asymptomatic carriers (8/10, 80%), and tended to drop to lower levels as the disease progressed to liver cirrhosis (0/8) while leukocyte HBV DNA-positive rates were highest in patients with cirrhosis (4/8, 50%). The results also show that in individuals who were serologically negative for hepatitis B surface antigen (HBsAg) and positive for antibodies to HBsAg and/or HBcAg, HBV DNA was absent in most of the sera (27/28, 96%) but it was present in leukocytes of some of these patients (7/28, 25%). In control experiments with 11 healthy individual, HBV DNA was not detected in either sera or leukocytes. In all the cases with leukocyte HBV DNA, the HBV DNA molecules were present in free forms with discrete sizes. The exceptions were a case of liver cirrhosis and a case of chronic hepatitis with possible HBV sequence integration into high molecular weight cellular DNA. Since HBV does infect human leukocytes, it may perhaps interfere with the immunological functions of the white blood cells, and thus play an important role in the pathogenesis of HBV-induced liver disease.

Carcinoma, Hepatocellular↗
PubMed1986

Restriction fragment length polymorphism of the human beta-globin gene cluster: analysis of a beta-thalassemic family in Taiwan.

We have analysed seven polymorphic restriction sites of the human beta-globin gene cluster of six members of a Chinese family with a beta +-thalassemic sibling. The seven polymorphic sites analysed are the HincII site at the 5'-end of the epsilon-globin gene, the HindIII sites in the two gamma-globin genes, two HincII sites within and at the 3'-end of the psi beta 1 pseudogene, the AvaII site in the beta-globin gene and the BamHI site located at the 3' side of the beta-globin gene. The beta thal chromosome has been identified to have a haplotype of +----++ with respect to these seven polymorphic sites. This is also the most predominant haplotype associated with beta +-thalassemia in Mediterranean and Chinese populations (Chen et al., 1984; Orkin et al., 1982). Of the seven sites analysed in this family, four will be useful in prenatal diagnosis of beta-thalassemia in subsequent pregnancies in the family.

DNA Restriction Enzymes↗
PubMed1985

Characteristics of hepatitis B surface antigen produced in yeast.

We have constructed an expression plasmid for regulated expression of the hepatitis B surface antigen gene in yeast using promoter of the yeast Pho5 gene. In the yeast transformants, the monomeric HBsAg (22K dalton) was estimated to constitute approximately 3% of the total proteins. On extraction, the HBsAg was found to have a buoyant density of 1.18 g/ml and an Sw.20 value of 54. Electron microscopy revealed particles of heterogeneous size ranging from 18-28 nm. When the yeast HBsAg was used to immunize guinea pigs, the anti-HBsAg antibodies produced could react with human serum HBsAg.

Animals↗
PubMed1985

Characterization of restriction endonuclease maps of hepatitis B viral DNAs.

The HBV DNA isolated from Dane particles of 9 patients' plasma was cloned into the EcoRI or BamHI site of the pUC8 plasmids. Two plasmids with full length HBV DNA and four plasmids containing the HBV surface antigen gene were obtained. Based on our cloned HBV DNA and a comparison with 7 complete sequences and 5 restriction endonuclease patterns of HBV DNA published by others, we can recognize common restriction sites shared by different subtypes (adw, adr, ayw, and adyw): (1) a HincII site in the S gene, (2) a BamHI site in the X region, and (3) two BglII sites in the C gene. In addition adw has specific sites for HincII, BamHI, and PstI in the pre-S region. A unique XhoI site is present in the pre-S region in all subtypes except for adw.

Bacterial Proteins↗
PubMed1985

Restriction endonuclease mapping of the hepatitis B viral genome isolated from Taiwan.

The Eco RI fragment of hepatitis B virus (HBV) DNA isolated from human blood plasma Dane particles were inserted into plasmid pUC8 Eco RI site and transformed into E. coli JM103 host. Two recombinants pTWL1 and pTWL2 were found to carry 3.2 kbp fragment and proved to have HBV genome by Southern hybridization method. The 1.4 kbp Bam HI fragment which carried the hepatitis B viral surface antigen (HBsAg) gene, obtained via Bam HI digestion of Dane particles DNA which was made fully double stranded by endogenous DNA polymerase reaction, was also inserted into plasmid pUC8 Bam HI site. Four recombinant clones, pTWS1, pTWS2, pTWS3, and pTWS4 were found. Only one of the clones pTWS1 carried the HBsAg gene in a correct orientation with respect to the lac promoter sequence. The physical mapping of HBV DNA was performed with several restriction endonucleases. Our results indicated that the HBV DNA insert contains unique XbaI and HpaI cleavage sites and lacks the cleavage sites for the HindIII, SmaI, KpnI, SalI, and SstI endonucleases. The locations of Bam HI, BglII, and HincII endonucleases cleavage sites within the cloned HBV DNA of the pTWL1 plasmid were similar to that HBV DNA of adw and adw2 subtypes.

Chromosome Mapping↗