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J Tam

Publications and source records attributed to J Tam.

At least 37 records · Page 2Linked to original sources
PubMed1995

An STS-based map of the human genome.

A physical map has been constructed of the human genome containing 15,086 sequence-tagged sites (STSs), with an average spacing of 199 kilobases. The project involved assembly of a radiation hybrid map of the human genome containing 6193 loci and incorporated a genetic linkage map of the human genome containing 5264 loci. This information was combined with the results of STS-content screening of 10,850 loci against a yeast artificial chromosome library to produce an integrated map, anchored by the radiation hybrid and genetic maps. The map provides radiation hybrid coverage of 99 percent and physical coverage of 94 percent of the human genome. The map also represents an early step in an international project to generate a transcript map of the human genome, with more than 3235 expressed sequences localized. The STSs in the map provide a scaffold for initiating large-scale sequencing of the human genome.

Animals↗
PubMed1995

Evidence that immunosuppression is an intrinsic property of the alpha-fetoprotein molecule.

Among the proteins that comprise the albumin family, alpha-fetoprotein (AFP) is the only member which exhibits immunoregulatory properties. However, some investigations have argued that AFP-mediated immunosuppression is not an inherent property of the molecule itself, but is instead, hypothesized to be either a function of a low molecular weight inhibitor bound to AFP or to a post-translational modification of the protein. AFP cannot be isolated from natural sources in quantities sufficient for the detailed biochemical and functional analyses required to resolve these issues. We have therefore produced recombinant forms of the protein (rAFP) by cloning the cDNA's for mouse and human AFP in both eukaryotic and prokaryotic expression systems. As described in this report, we were able to abundantly express rAFP's in bacterial, baculovirus and yeast expression systems. Recombinant proteins derived from each expression system were recognized by polyclonal and monoclonal anti-AFP antibodies as determined by immunoblot analysis. Pure recombinant protein samples, as characterized by polyacrylamide gel analyses, N-terminal sequencing and FPLC and HPLC chromatography, were evaluated for their immunoregulatory properties in murine and human in vitro immunological assays. The results of these studies establish that rAFP is functionally equivalent to natural fetal derived AFP molecules. Importantly, the data reported here demonstrate that AFP-mediated immunoregulation is an activity intrinsic to the molecule itself and cannot be attributed to either putative non-covalently bound moieties or to post-translational modifications such as glycosylation and sialylation. These studies provide a basis for initiating detailed investigations into the potential clinical usefulness of AFP as an immunotherapeutic agent.

Amino Acid Sequence↗
PubMed1994

The influence of adenine-rich motifs in the 3' portion of the ribosome binding site on human IFN-gamma gene expression in Escherichia coli.

The ribosome binding site (RBS) of prokaryotic mRNA is divided into 5' and 3' portions by the translation initiation codon. Although it is well known that the presence of an appropriate RBS containing only the 5' portion is sufficient to direct the initiation of protein synthesis, the 3' portion appears to play a significant role in modulating the initiation process as well. Here we examine the influence of adenine-rich motifs frequently found in the 3' portion of highly expressed prokaryotic mRNAs. Two synthetic DNA fragments, GAGAAAAAAATC (corresponding to the first 12 nucleotides following the initiation codon of the chloramphenicol acetyltransferase gene), and AAAAAAATTAA were used to modify the beginning of the coding region of the human immune interferon-gamma (IFN-gamma) gene. The level of the protein synthesis in Escherichia coli directed by plasmids containing these constructs was quantitated. We found that placing either adenine-rich motif in the 3' portion of the RBS strongly enhanced gene expression, probably through an effect on translation initiation. We have also compared the protein expression levels of these gene constructs containing different series of 5'-RBSs with varying precistronic lengths and Shine-Dalgarno sequence lengths. The results suggest a positive functional role for the 3' adenine-rich motif. A possible mechanism for these effects is discussed.

Adenine↗
PubMed1993

Systemic absorption of salbutamol following nebulizer delivery in acute asthma.

We measured plasma salbutamol concentrations in 35 children with acute asthma attacks before and after nebulizer therapy. The main finding was that older children had higher concentrations than younger children, despite similar dosage regimens. There was no influence of severity of the asthma attack on the following measures: pre- and post-nebulizer concentrations, absolute and percentage change in salbutamol levels with therapy. We conclude that the theoretical risks of high concentrations in young children were not found and we suggest that the very young may indeed require higher doses due to possible problems in nebulizer technique or differences in kinetics.

Absorption↗
PubMed1992

In vivo chemical footprinting of the Escherichia coli ribosome.

We have studied the in vivo chemical accessibility of 16S rRNA residues A349-G1505 in the small subunit of the Escherichia coli ribosome. Exponentially growing E. coli cultures were reacted with dimethyl sulfate, and the reactive sites on the 16S ribosomal RNA were analyzed by reverse transcription, an assay which detects reactions at N1-A and N3-C. In agreement with previous in vitro results, three regions of 16S RNA appeared particularly reactive to dimethyl sulfate: hairpin 27 (residues A892-A915) of the central domain, and hairpin 33-33A (residues A994-C1037) and the tip of hairpin 41 (residues A1256-A1275), both from the 3' major domain. These three regions contained 52% of the reactive residues but only 8% of the residues scanned. In contrast to previous in vitro results, three small sections of 16S RNA appeared protected: the tip of hairpins 26 (residue A845) and 31 (residues A968-A969), and residues A1418, A1441, and A1483 of the middle body of hairpin 44. Four of the dimethyl sulfate reactive sites (A831, C948, A1019, and C1192) are located in positions usually assumed to be double-stranded (helices 26, 30, 33-33A, and 34), which suggests alternative structures for these helices at least during part of the translation process, as if the residues in question belonged to "conformational switches." The addition of chloramphenicol protected residues A831, A1035-A1036, and A1503, which suggests that they belong to the mobile regions of the elongating ribosome, and become exposed during some transition(s) from one ribosomal state to the other during the elongation cycle.

Adenosine↗
PubMed1992

Arithmetic versus harmonic mean values for cyclosporin-A pharmacokinetic parameters.

The harmonic and arithmetic mean values for volume of distribution at steady state, half-life, and clearance of intravenous cyclosporin-A were calculated using an index set of 22 renal transplant candidates to determine if harmonic mean values provide a less biased estimate of central tendency than arithmetic mean values. Cyclosporin-A was measured using a nonspecific radioimmune assay method. The arithmetic mean value for volume of distribution was 16% larger than calculations by the harmonic mean method. Similarly, the arithmetic mean half-life and clearance values were larger than harmonic mean values by 10% and 15%, respectively. However, 95% confidence intervals for these pharmacokinetic parameters overlapped. When these mean pharmacokinetic parameter values were used to predict actual values in a test group of 22 renal transplant candidates receiving cyclosporin-A, similar levels of precision were demonstrated by either method. Both methods produced positively biased predictions for volume of distribution and clearance. However, these differences were not significant. These findings suggest there is little practical value for the use of harmonic mean calculations to describe the central tendency of pharmacokinetic parameters of cyclosporin-A under the conditions studied. The value of harmonic mean values for pharmacokinetic parameters in other patient populations or with other assay methods for cyclosporin remain to be studied.

Bias↗
PubMed1991

Interaction of ribosomal protein S1 and initiation factor IF3 with the 3' major domain and the decoding site of the 30S subunit of Escherichia coli.

We have studied the effect of the binding of ribosomal protein S1 and initiation factor IF3 on the accessibility of nucleotide residues 584-1506 in the small subunit of the Escherichia coli ribosome. Protein S1 strongly decreases RNase V1 attack at G1164, in hairpin 40 of the 3' major domain, and weakly decreases DMS attack at C1302, in the central loop of the 3' major domain, and at A1503, in the 3' minor domain. It also weakly increases the DMS reactivity of A1004, in the 3' major domain, and of A901, in the central domain. Factor IF3 strongly decreases RNase V1 attack (but not dimethyl sulfate attack) at A1408, in the decoding site, and weakly protects A1500, in the 3' minor domain and near the colicin E3 cleavage site. Neomycin does not interfere with this effect of IF3, but IF3 interferes with the protective effect of neomycin against dimethyl sulfate attack at A1408.

Base Sequence↗
PubMed1989

Nosocomial gastroenteritis in paediatric patients.

Between November 1982 and April 1985, 2228 children under the age of 5 years with acute gastroenteritis were admitted to the paediatric isolation ward of Queen Mary Hospital, Department of Paediatrics, University of Hong Kong. In 56.2% the causative agent was identified as rotavirus, Salmonella, Campylobacter, Shigella, Escherichia coli or a combination of these pathogens. Our isolation procedures included cohort nursing of all diarrhoeal patients in two separate rooms (each accommodating 6 patients), barrier gowns and stringent handwashing with chlorhexidine. A total of 163 cases (13.4% of all positive cases) were identified as nosocomial infections. Rotavirus was the responsible agent for nosocomial infection in 128 cases (20% of all rotavirus infection). There were 35 patients with bacterial nosocomial infection, (7% of all the bacterial positive cases). Nosocomial rotavirus gastroenteritis was 3.4 times more frequent than nosocomial gastroenteritis due to bacterial pathogens. We conclude that modification of our present isolation procedures is necessary in order to reduce rotavirus nosocomial infection.

Bacterial Infections↗
PubMed1989

The impact of body weight on cyclosporine pharmacokinetics in renal transplant recipients.

In order to assess the effect of body weight on cyclosporine disposition, 45 adult uremic candidates for renal transplantation underwent detailed nutritional assessment and pharmacokinetic analysis. There were 10 obese and 35 nonobese patients defined as actual body weight (ABW) greater than 125 Per cent of ideal body weight (IBW), and arm fat area greater than 90th percentile. There was no significant difference in demographic variables such as age, sex, number of diabetics, IBW, serum lipids, or liver function tests between the 2 groups. Although there was a significant difference in ABW, pharmacokinetic analyses failed to demonstrate significant differences in bioavailability, elimination half-life, clearance, or apparent steady state volume of distribution when these calculations were normalized by IBW, body surface area, or as absolute values. Multiple stepwise linear regression failed to demonstrate a significant correlation between serum lipids or body size measurements and these parameters. When dosed according to ABW, obese recipients of renal allografts had a mean serum RIA trough level of 227 ng/ml as compared to 121 ng/ml in nonobese recipients on day 7. Therefore in order to achieve comparable drug concentrations in the early transplant period, CsA should be given to obese patients based on their IBW.

Adult↗
PubMed1989

Microbiology and antibiotics in infectious abdominal emergencies.

The appropriate treatment of intra-abdominal infection is often confusing and controversial. Much of the controversy is due to the availability of a substantial number of newer, broad-spectrum antimicrobials. An understanding of the spectrum of activity, toxicity, and clinical efficacy of these drugs is critical in the selection of therapy for the treatment of intra-abdominal sepsis.

Abdomen, Acute↗
PubMed1987

Loss of growth responsiveness to epidermal growth factor and enhanced production of alpha-transforming growth factors in ras-transformed mouse mammary epithelial cells.

A mouse mammary epithelial cell line, NMuMG, exhibits a low capacity to grow in semisolid medium as colonies and it is not tumorigenic in nude mice. In contrast, NMuMG cells which have been transformed by an activated c-Harvey ras proto-oncogene, NMuMG/rasH, or by the polyoma middle T-transforming gene, NMuMG/pyt, are able to grow in soft agar and, when injected into nude mice, produce undifferentiated carcinomas. Human epidermal growth factor (EGF) or human alpha-transforming growth factor (alpha TGF) can stimulate, in a dose-dependent fashion, the anchorage-independent growth of NMuMG and NMuMG/pyt cells in soft agar but fail to enhance the anchorage-independent growth of the NMuMGrasH cells. Likewise, human EGF or human alpha TGF is also able to stimulate the anchorage-dependent growth of normal NMuMG cells and NMuMG/pyt cells in a serum-free medium supplemented with insulin, transferrin, fetuin, and laminin, or in medium containing low concentrations of serum, whereas these same growth factors under comparable culture conditions have little or no effect upon the anchorage-dependent growth of the ras-transformed NMuMG-rasH cells. The biological refractoriness of the NMuMG/rasH cells to human EGF or human alpha TGF is reflected by a reduction in the total number of cell surface receptors for EGF and by an absence of a high-affinity population of binding sites for mouse [125l]EGF on these cells as compared to the NMuMG or NMuMG/pyt cells. In addition, concentrated conditioned medium (CM) obtained from NMuMG/rasH and NMuMG/pyt cells contains a relatively higher amount of biologically active TGFs than CM obtained from comparably treated NMuMG cells as measured by the ability to induce the anchorage-independent growth of normal rat kidney cells in soft agar. The higher levels of biologically active TGFs found in the CM from the transformed cells relative to the NMuMG cells is paralleled by a corresponding increase in the CM from these cells in the amount of immunoreactive alpha TGF, by an increase in the amount of EGF receptor-competing activity, and by an increase in the levels of alpha TGF mRNA in the NMuMG/rasH cells. These results demonstrate that mammary epithelial cells which have been transformed by an activated ras proto-oncogene, but not by the polyoma middle T-transforming gene, become unresponsive to exogenous EGF or alpha TGF.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Chemical synthesis and expression of the human calcitonin gene.

A gene coding for the peptide hormone, human calcitonin (hCT), has been constructed and expressed in bacteria using a prokaryotic vector containing the strong T5P25 promoter and a strong ribosome-binding site. The bacterial hCT is different from the natural hCT by having an additional Met residue at the N terminus and a non-amidated C terminus. Despite these differences, the bacterial hCT is biologically active in rat cells. The results are important for future structure-function relationship studies using mutants constructed by genetic engineering.

Amino Acid Sequence↗
PubMed1986

Immunological detection and quantitation of alpha transforming growth factors in human breast carcinoma cells.

Alpha transforming growth factors (alpha TGFs) were immunologically detected in the concentrated conditioned medium (CM) prepared from four human breast cancer cell lines and from primary cultures of human mammary epithelial cells, and in the tissue extracts prepared from normal, benign, and malignant breast biopsies. Immunoreactive alpha TGFs were quantitated by a competitive radioimmunoassay (RIA) using affinity-purified polyclonal sheep anti-rat alpha TGF antibodies which react with human alpha TGF but not with human epidermal growth factor (EGF). The relative level of RIA-detectable alpha TGFs in the CM from the breast cancer cell lines MCF-7, ZR-75-1, T47-D, and MDA-MB-231, and from the CM of primary cultures of human mammary epithelial cells, ranged from 0.02 to 0.85 ng/ml. MCF-7 or ZR-75-1 cells grown in the presence of 17 beta-estradiol (10(-8) M) for 48 h were found to release two- to three-fold more alpha TGFs into their CM than the same cells grown in the absence of estrogen. In detergent extracts prepared from normal breast tissue, a benign fibrocystic lesion, fibroadenomas and primary breast carcinomas, the relative alpha TGF concentrations were found to range from 1.5 to 6 ng/mg cell protein. No significant correlations were found between the alpha TGF levels and the pathological state of the tissues, the estrogen receptor status of the tumors, or the relative amounts of the ras gene protein p21ras in the tissues as determined by Western immunoblot analysis. The question of biological relevancy of alpha TGF for human mammary tumors will require further studies on synthesis and turnover of alpha TGF, the relationship between immunoreactivity and biological activity of alpha TGF, and differences in biological responsiveness of mammary tumor cells.

Breast Neoplasms↗
PubMed1985

Molecular cloning and nucleotide sequence of the alpha and beta subunits of allophycocyanin from the cyanelle genome of Cyanophora paradoxa.

The genes for the alpha- and beta-subunit apoproteins of allophycocyanin (AP) were isolated from the cyanelle genome of Cyanophora paradoxa and subjected to nucleotide sequence analysis. The AP beta-subunit apoprotein gene was localized to a 7.8-kilobase-pair Pst I restriction fragment from cyanelle DNA by hybridization with a tetradecameric oligonucleotide probe. Sequence analysis using that oligonucleotide and its complement as primers for the dideoxy chain-termination sequencing method confirmed the presence of both AP alpha- and beta-subunit genes on this restriction fragment. Additional oligonucleotide primers were synthesized as sequencing progressed and were used to determine rapidly the nucleotide sequence of a 1336-base-pair region of this cloned fragment. This strategy allowed the sequencing to be completed without a detailed restriction map and without extensive and time-consuming subcloning. The sequenced region contains two open reading frames whose deduced amino acid sequences are 81-85% homologous to cyanobacterial and red algal AP subunits whose amino acid sequences have been determined. The two open reading frames are in the same orientation and are separated by 39 base pairs. AP alpha is 5' to AP beta and both coding sequences are preceded by a polypurine, Shine-Dalgarno-type sequence. Sequences upstream from AP alpha closely resemble the Escherichia coli consensus promoter sequences and also show considerable homology to promoter sequences for several chloroplast-encoded psbA genes. A 56-base-pair palindromic sequence downstream from the AP beta gene could play a role in the termination of transcription or translation. The allophycocyanin apoprotein subunit genes are located on the large single-copy region of the cyanelle genome.

Amino Acid Sequence↗
PubMed1982

Molecular defects in beta-thalassemia.

Our studies have shown that globin-gene structure, as revealed by Southern blot analysis, is normal in most patients who are homozygous for beta-thalassemia. In many, but not all patients, evidence for mutations which alter the metabolism of beta-globin RNA molecules was obtained by several methods of analysis. The most specific and sensitive of these involves the use of single-stranded, highly radioactive probes generated using the M13 cloning system. Such probes allow detection of aberrantly processed RNA molecules by S1 nuclease analysis, thereby providing clues as to the position and nature of mutations within individual thalassemic globin genes. Of greatest potential interest are those genes which provide no evidence, in bone marrow RNA, of aberrantly processed intermediates. Analysis of these genes by molecular cloning and DNA sequencing may lead to identification of sequences which are important for initiation or termination of RNA transcription. Mutations which cause beta-thalassemia continue to provide a rich source of information about the nature of DNA sequences which are essential for efficient gene expression. By study of thalassemic patients, new insights are obtained into normal mRNA metabolism.

Base Sequence↗