Search PubMed⌕ Search

Biomedical subjects

J Kwak

Publications and source records attributed to J Kwak.

28 records · Page 2Linked to original sources
PubMed1996

Identification of bldA mutants of Streptomyces griseus.

The bldA gene (encoding tRNA(UUA)Leu) from Streptomyces griseus (Sg) was cloned by hybridization with bldA from Streptomyces coelicolor (Sc). Introduction of Sg bldA into Sc bldA mutants restored sporulation and actinorhodin production. Sporulation of a subset of Sg bald mutants, which produce no aerial mycelium or spores, was restored in the presence of bldA from Sc or Sg. The nucleotide sequences of the bldA alleles from two such bald mutants revealed point mutations in the anticodon stem and the T psi C stem.

Anthraquinones↗
PubMed1996

Analysis of a gene that suppresses the morphological defect of bald mutants of Streptomyces griseus.

When present in multiple copies, orf1590 restored sporulation to class IIIA bald mutants of Streptomyces griseus, which form sporulation septa and thick spore walls prematurely. The orf1590 alleles from class IIIA bald mutants restored sporulation upon introduction at a high copy number into those same mutants, and the nucleotide sequence of one of these alleles was identical to that of the wild-type strain. We conclude that overexpression of orf1590 suppresses the defect in class IIIA bald mutants. Previous nucleotide sequence and transcript analyses suggested that orf1590 could encode two related proteins, P56 and P49.5, from nested coding sequences. A mutation that prevented the synthesis of P56 without altering the coding sequence for P49.5 eliminated the function of orf1590, as did amino acid substitutions in the putative helix-turn-helix domain located at the N terminus of P56 and absent from P49.5. To determine the coding capacity of orf1590, we analyzed translational fusions between orf1590 and the neo gene from Tn5. Measurement of the expression of fusions to the wild-type and mutant alleles of orf1590 indicated that P56 was the sole product of orf1590 during vegetative growth. Attempts to generate a nonfunctional frameshift mutation in orf1590 were unsuccessful in the absence of a second-site bald mutation, suggesting that orf1590 may be required during vegetative growth by preventing early sporulation. Our results are consistent with the hypothesis that P56 at a high level delays the premature synthesis of sporulation septa and spore walls in class IIIA mutants.

Amino Acid Sequence↗
PubMed1996

Bald mutants of Streptomyces griseus that prematurely undergo key events of sporulation.

To identify the structural defects of nonsporulating mutants of Streptomyces griseus, the wild-type strain and class III bald mutants were examined by using transmission electron microscopy, ultrasonic treatment, and fluorescence microscopy after the induction of submerged sporulation by phosphate starvation. In the wild-type strain, submerged sporulation was marked by the relatively synchronous formation of sporogenic hyphae, nucleoid segregation, deposition of sporulation septa, and subsequent thickening of the spore walls during maturation. All of the class III mutants prematurely synthesized sporulation septa and thick spore walls. The class IIIA and C mutants formed sporogenic hyphae earlier than the wild-type strain and underwent nucleoid segregation in parallel with sporulation septum formation. In the class IIIB (bld4) mutant, DNA segregation appeared to be uncoupled from septum formation. The results indicate that the class III mutants are defective in loci that are involved in the regulation of key events of Streptomyces morphogenesis.

DNA, Bacterial↗
PubMed1995

HLA-DQA1 and HLA-DQB1 haplotypes in aborted fetuses and couples with recurrent spontaneous abortion.

HLA haplotypes may be associated with spontaneous abortion through a variety of mechanisms, including maternal hyporesponsiveness to fetal alloantigens, maternal autoimmunity, and HLA-linked t-locus homologues. HLA-DQA1 and HLA-DQB1 haplotypes were determined in 37 couples with a history of recurrent spontaneous abortion (RSAB), 40 of their abortuses, and 20 fertile control couples. The distribution of haplotype frequencies did not differ between control subjects and RSAB wives, RSAB husbands, or abortuses. The frequency of the HLA-DR5-linked haplotype, DQA1*501/DQB1*301, which was considered a marker for immune hyporesponsiveness, did not differ between RSAB wives and control subjects (P = 0.353). The frequency of the autoimmune-associated HLA-DR3-linked haplotype, DQA1*0501/DQB1*0201, did not differ significantly between RSAB wives and control subjects (P = 0.103). The frequency of the DQA1*0201/DQB1*0201 haplotype in RSAB husbands was greater than the 95th percentile confidence limit of the frequency of this haplotype in control subjects. Among seven RSAB husbands who were heterozygous for this haplotype and did not share a DQA1*0201 allele with his wife, the haplotype was transmitted to 6 of 7 abortuses (3.5 expected). Although the small size of this sample precludes drawing conclusions regarding HLA transmission biases in RSAB couples, these data have generated a specific hypothesis regarding the DQA1*0201/DQB1*0201 haplotype that can be investigated in future studies.

Abortion, Habitual↗
PubMed1995

Pathways of Rb+ influx and their relation to intracellular [Na+] in the perfused rat heart. A 87Rb and 23Na NMR study.

The aims of this study were to characterize the routes of influx of the K+ congener, Rb+, into cardiac cells in the perfused rat heart and to evaluate their links to the intracellular Na+ concentration ([Na+]i) using 87Rb and 23Na nuclear magnetic resonance (NMR) spectroscopy. The rate constant for Rb+ equilibration in the extracellular space was 8.5 times higher than that for the intracellular space. The sensitivity of the rate of Rb+ accumulation in the intracellular space of the perfused rat heart to the inhibitors of the K+ and Na+ transport systems has been analyzed. The Rb+ influx rates were measured in both beating and arrested hearts: both procaine (5 mmol/L) and lidocaine (1 mmol/L) halved the Rb+ influx rate. In procaine-arrested hearts, the Na+,K(+)-ATPase inhibitor ouabain (0.6 mmol/L) decreased Rb+ influx by 76 +/- 24% relative to that observed in untreated but arrested hearts. Rb+ uptake was insensitive to the K+ channel blocker 4-aminopyridine (1 mmol/L). The inhibitor of Na+/K+/2 Cl- cotransport bumetanide (30 mumol/L) decreased Rb+ uptake only slightly (by 9 +/- 8%). Rb+ uptake was dependent on [Na+]i: it increased by 58 +/- 34% when [Na+]i was increased with the Na+ ionophore monensin (1 mumol/L) and decreased by 48 +/- 9% when [Na+]i was decreased by the Na+ channel blockers procaine and lidocaine. Dimethylamiloride (15 to 20 mumol/L), an inhibitor of the Na+/H+ exchanger, slightly reduced [Na+]i and Rb+ entry into the cardiomyocytes (by 15 +/- 5%). 31P NMR spectroscopy was used to monitor the energetic state and intracellular pH (pHi) in a parallel series of hearts. Treatment of the hearts with lidocaine, 4-aminopyridine, dimethylamiloride, or bumetanide for 15 to 20 minutes at the same concentrations as used for the Rb+ and Na+ experiments did not markedly affect the levels of the phosphate metabolites or pHi. These data show that under normal physiological conditions, Rb+ influx occurs mainly through Na+,K(+)-ATPase; the contribution of the Na+/K+/2 Cl- cotransporter and K+ channels to Rb+ influx is small. The correlation between Rb+ influx and [Na+bdi during infusion of drugs that affect [Na+]i indicates that, in rat hearts at 37 degrees C, Rb+ influx can serve as a measure of Na+ influx. We estimate that, at normothermia, at least 50% of the Na+ entry into beating cardiac cells is provided by the Na+ channels, with only minor contributions (< 15%) from the Na+/K+/2 Cl- cotransporter and the Na+/H+ exchanger.

Animals↗
PubMed1993

MHC class II compatibility in aborted fetuses and term infants of couples with recurrent spontaneous abortion.

Maternal-fetal histocompatibility for alleles at HLA class II loci, HLA-DQA1 and HLA-DQB1, was examined in 40 abortuses and 31 liveborn children of 68 couples with a history of idiopathic recurrent spontaneous abortion (RSAB) who underwent leukocyte immunization prior to the index pregnancy. Significantly more couples with RSAB shared two HLA-DQA1 alleles as compared with fertile control couples (0.18 vs. 0.03, respectively; P = 0.031). There were no differences in HLA sharing between couples with RSAB who experienced a repeat abortion in the index pregnancy as compared with couples with RSAB who were delivered of a liveborn child. Non-significant deficits of abortuses who were compatible for alleles at the HLA-DQA1 (6 observed vs. 8.5 expected; P = 0.225) and the HLA-DQB1 (7 observed vs. 9.2 expected; P = 0.254) loci were observed. A significant deficit of HLA-DQA1 compatible liveborn children was observed (1 observed vs. 5.5 expected; P = 0.0069). The overall deficit of HLA-DQA1 compatible fetuses (7 observed vs. 14.0 expected; P = 0.0018) after approximately 8 weeks gestation suggests that HLA-DQA1 compatible fetuses may be aborted early in pregnancy, prior to the time when fetal tissue can be recovered for genetic studies.

Abortion, Habitual↗
PubMed1992

Molecular analysis of sporulation in Streptomyces griseus.

Previous evidence suggested that orf1590 from Streptomyces griseus has the potential to encode two polypeptide products from temporally regulated nested open frames (orfs) and that the longer polypeptide may be a DNA-binding protein. We have developed a hypothetical model of the role of orf1590 in sporulation of S. griseus and have begun to test this model by determining the nucleotide sequence of the orf1590 counterpart from Streptomyces coelicolor. The conservation of the helix-turn-helix domain and the two potential translation start codons is consistent with our model. Continued analysis of bald mutants of S. griseus has indicated that several prematurely synthesize sporulation septa and spore walls. One of these nonsporulating strains appears to be a bldA mutant of S. griseus. Complementation analysis suggests that at least three genetic loci are involved in the correct timing of deposition of sporulation septa and wall thickening.

Amino Acid Sequence↗
PubMed1990

Application of scanning electrochemical microscopy to biological samples.

The scanning electrochemical microscope can be used in the feedback mode in two-dimensional scans over biological substrates to obtain topographic information at the micrometer level. In this mode, the effect of distance between a substrate (either conductive or insulating) and a scanning ultramicroelectrode tip on the electrolytic current flowing at the tip is recorded as a function of the tip x-y position. Scans of the upper surface of a grass leaf and the lower surface of a Ligustrum sinensis leaf (which show open stomata structures) immersed in aqueous solution are shown. Scans of the upper surface of an elodea leaf in the dark and under irradiation, where the tip reaction is the reduction of oxygen produced by photosynthesis, demonstrate the possibility of obtaining information about the distribution of reaction sites on the substrate surface.

Electrochemistry↗
PubMed1987

Cloning of murine megakaryocyte progenitor cells in a fibrin clot culture system.

A fibrin clot culture system was applied to the cloning of mouse megakaryocyte colony-forming cells (CFU-Meg). The culture medium in this new method consists of Iscove's minimal essential medium containing fetal bovine serum, bovine fibrinogen, bovine thrombin, and pokeweed mitogen-stimulated mouse spleen cell-conditioned medium (PWM-SCM). CFU-Meg colony frequency with 10% PWM-SCM was maximal on days 5-6 of culture. Plating efficiencies averaged 36.1 +/- 3.9 and 51.9 +/- 6.0 per 1.5 X 10(5) BDF1 bone marrow cells and 1.0 X 10(6) spleen cells, respectively. The addition of bovine serum albumin to the culture medium had no effect on the efficiency of megakaryocyte colony growth in this culture system. This simplified and reproducible culture system supported not only the growth of colonies composed of megakaryocytes in "synchronous maturation," but also so-called "heterogenous" megakaryocyte colonies composed of cells in all stages of maturation.

Animals↗