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Biomedical subjects

S Yun

Publications and source records attributed to S Yun.

32 records · Page 2Linked to original sources
PubMed1997

Suppression of MHC class II expression by human class II trans-activator constructs lacking the N-terminal domain.

The class II trans-activator (CIITA) is a bi- or multi-functional domain protein which plays a critical role in the expression of MHC class II genes. We report that removal of the N-terminal 151 amino acids, encompassing all of the acidic domain but leaving intact the proline/serine/threonine-rich domain, results in a mutant protein with potent suppressive properties for MHC class II expression. HeLa cells stably or transiently transfected with mutant CIITA constructs showed up to 99% suppression of MHC class II antigen induction by IFN-gamma and marked suppression of HLA-DRA mRNA expression. Transient transfection of a B lymphoma line resulted in up to 89% reduction of constitutive MHC class II expression within 5 days and suppression of HLA-DRA mRNA synthesis.

B-Lymphocytes↗
PubMed1996

Similarities in the architecture of the active sites of Ni-hydrogenases and Fe-hydrogenases detected by means of infrared spectroscopy.

Three groups that absorb in the 2100-1800-cm-1 infrared spectral region have recently been detected in Ni-hydrogenase from Chromatium vinosum [Bagley, K.A., Duin, E.C., Roseboom, W., Albracht, S. P.J. & Woodruff, W.H. (1995) Biochemistry 34, 5527-5535]. To assess the significance and generality of this observation, we have carried out an infrared-spectroscopic study of eight hydrogenases of three different types (nickel, iron and metal-free) and of 11 other iron-sulfur and/or nickel proteins. Infrared bands in the 2100-1800-cm-1 spectral region were found in spectra of all Ni-hydrogenases and Fe-hydrogenases and were absent from spectra of any of the other proteins, including a metal-free hydrogenase. The positions of these bands are dependent on the redox state of the hydrogenase. The three groups in Ni-hydrogenases that are detected by infrared spectroscopy are assigned to the three unidentified small non-protein ligands that coordinate iron in the dinuclear Ni/Fe active site as observed in the X-ray structure of the enzyme from Desulfovibrio gigas [Volbeda, A., Charon, M.-H., Piras, C., Hatchikian, E.C., Frey, M. & Fontecilla-Camps, J.C. (1995) Nature 373, 580-587]. It is concluded that these groups occur exclusively in metal-containing H2-activating enzymes. It is proposed that the active sites of Ni-hydrogenases and of Fe-hydrogenases have a similar architecture, that is required for the activation of molecular hydrogen.

Binding Sites↗
PubMed1996

Functional conservation of yeast mtTFB despite extensive sequence divergence.

Transcription of mtDNA in the yeast S. cerevisiae depends on recognition of a consensus nonanucleotide promoter sequence by mtRNA polymerase acting with a 40-kDa dissociable factor known as mtTFB or Mtflp. mtTFB has been cloned and characterized in S. cerevisiae, but has not been studied in similar detail in any other organism. Although it is known that mitochondrial transcription in the dairy yeast, Kluyveromyces lactis, initiates within the same consensus promoter sequence used in S. cerevisiae, no previous studies have focused on the proteins involved in transcription initiation in K. lactis. In this article, we report the cloning of mtTFB from K. lactis and from a yeast more closely related to S. cerevisiae, S. kluyveri. Both novel mtTFB genes were able to substitute for the MTF1 gene in S. cerevisiae. Both proteins purified following expression in E. coli were able to support specific transcription initiation in vitro with the S. cerevisiae mtRNA polymerase. The S. kluyveri and K. lactis mtTFB proteins share only 56% and 40% identity with S. cerevisiae mtTFB, respectively. Alignments of the three mtTFB sequences did not reveal any regions larger than 30 amino acids with greater than 60% amino acid identity. In particular, regions proposed to show sequence similarity to bacterial sigma factors were not more highly conserved than other regions of the mtTFB proteins. All three yeast mtTFB genes lack conventional amino-terminal mitochondrial targeting sequences, suggesting that all three proteins may be imported into mitochondria by the same unusual mechanism reported for S. cerevisiae mtTFB.

Amino Acid Sequence↗
PubMed1995

Hedamycin intercalates the DNA helix and, through carbohydrate-mediated recognition in the minor groove, directs N7-alkylation of guanine in the major groove in a sequence-specific manner.

BACKGROUND: The pluramycins are a class of antitumor antibiotics that exert their biological activity through interaction with DNA. Recent studies with the analog altromycin B have determined that these agents intercalate into the DNA molecule, position carbohydrate substituents into both major and minor grooves, and alkylate the DNA molecule by epoxide-mediated electrophilic attack on N7 of guanine located to the 3' side of the drug molecule. Alkylation is sequence dependent and appears to be modulated by glycoside substituents attached at the corners of a planar chromophore. The altromycin B-like analogs preferentially alkylate 5'AG sequences; hedamycin-like analogs prefer 5'TG and 5'CG sequences. Although the mechanism of guanine modification by altromycin B has been extensively studied, the mechanism of action of hedamycin has not been previously determined. RESULTS: Using high-field NMR, we have shown that hedamycin stacks to the 5' side of the guanine nucleotide at the site of intercalation in a DNA decamer, positioning both aminosaccharides into the minor groove to direct alkylation by the epoxide moiety on N7 of guanine. The C10 linked N,N-dimethylvancosamine sugar moiety interacts to the 5' side of the intercalation site, while the C8 linked anglosamine moiety interacts to the 3' side. The binding interactions of the two aminosugars steer the C2 double epoxide located in the major groove into the proximity of N7 of guanine. Unexpectedly, it is not the first epoxide that undergoes electrophilic addition to N7 of guanine, which would correspond to altromycin B, but the second, terminal epoxide. CONCLUSIONS: We have used two-dimensional NMR to elucidate the sequence-selective recognition of DNA by hedamycin and the mechanism of covalent modification of guanine by this antibiotic. Characterization of the intermolecular interactions between both hedamycin and altromycin B and their targeted DNA sequences has yielded a better understanding of the reasons for variations in sequence selectivity and alkylation reactivity among the pluramycin compounds.

Alkylation↗
PubMed1995

Functional and anatomical fiber analysis of the posterior commissure (PC) in the cat: evidence for PC fibers of which stimulation elicits non-oculosympathetic pupillary dilation.

Pupillary responses were studied by electrical stimulation of the posterior commissure (PC) and the nuclei of origin and termination of PC fibers in the cat. Prior to stimulation experiments, cervical sympathectomy was carried out to study the pupillary responses not mediated by the ocular sympathetic nerve. Pupillary responses were recorded by using an infrared pupillo-analyzing system. The stimulus consisted of a 5 s train of cathodal square wave (0.5 ms duration, 50 Hz) pulses. Stimulation of the PC evoked a pupillary response complex (PRC), which began with a rapid pupillary constriction after the latency of 210-317 ms. The threshold of constriction was 10 or 20 microA. Constriction reached its peak shortly after the onset of the stimulus, then the pupil gradually re-dilated (pupillary escape, PE) even though the stimulus was still lasting. The pupil gradually returned, after stimulus termination, to the size before stimulation in the cases with the pupil area before stimulation larger than 20 mm2. On the other hand, in the cases with smaller pupil area before stimulation (< 20 mm2), rapid constriction and PE were followed, after stimulus termination, by a large dilation (after-dilation, AD). The thresholds of PE and AD were 20 or 40 microA. Pupillary constriction was evoked with a large range of stimulus frequency (1-100 Hz). To evoke PE and AD, stimulus frequencies of 10 and 50 Hz were required respectively, and lower frequencies were ineffective. The peak latency of AD increased in proportion to the increase in stimulus frequency and intensity. Following horseradish peroxidase (dissolved in 5% alkyl-phenol ethylene oxide) injection into the pretectal region where fibers from the PC fan out, retrogradely labeled neurons occurred in many subthalamic, pretectal and midbrain nuclei on the other side. They were classified into three groups in terms of the pupillary response evoked by electrical stimulation; the pupillo-constrictory nuclei (PCNs) of which stimulation evoked constriction with the threshold of 20 microA, the pupillo-dilatory nuclei (PDNs) of which stimulation evoked dilation with the threshold of 20 or 10 microA, and other nuclei with higher thresholds of constriction or dilation. The PDNs were further, classified into two groups (Type 1 and Type 2 PDNs) according to the relationship between stimulus intensity and the peak latency of dilation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Neural mechanisms of pupillary abnormality following thalamic lesions: experimental lesion and stimulation studies in cats, and consideration of pupillary findings in thalamic vascular lesions.

Neural mechanisms of the pupillary abnormality in thalamic lesions were experimentally studied in cats. Moderate to considerable anisocoria appeared after kainic acid lesions involving the medial thalamus. The pupil on the side of the lesion was larger than its partner. Only subtle or no pupillary inequality was produced by lateral thalamic lesions. Electrical stimulation of the midline and medial thalamus evoked dilation bilaterally in sympathectomized pupils. Thus, pupillary dilation produced by stimulation of the thalamus was shown to be mediated in part by the oculomotor parasympathetic nerve (OPN). There was no threshold difference between ipsilateral (ipsi) and contralateral (contra) pupils. However, amplitude of dilation was significantly larger in the contra pupil than in the ipsi, when stimulus was given to the pupillo-dilatory medial thalamic nuclei. In these, the mediodorsal, parataenial, central dorsal, paracentral (Pc), and parafascicular nuclei and the medial division of the medial pulvinar nucleus were included. Pupillary dilation mediated by the ocular sympathetic nerve (OSN) was investigated by stimulating Pc and comparing the ipsi-contra difference in the amplitude of dilation between sympathectomized and non-sympathectomized pairs of pupils. In contrast to the results in sympathectomized pairs, there was no ipsi-contra difference in the amplitude of dilation or it was larger in the ipsi pupil in non-sympathectomized pairs. From these, it was inferred that stimulation of Pc activated OSN ipsilaterally or bilaterally with ipsi dominance. It was concluded that the medial and midline thalamus exerts pupillo-dilatory effects through a set of neural mechanisms; 1) ipsi-dominant bilateral OPN inhibition, and 2) ipsi or ipsi-dominant bilateral OSN activation. Neural mechanisms of the pupillary abnormality in thalamic vascular lesions were also considered.

Animals↗
PubMed1991

Postprostatectomy incontinence. Pathophysiology, evaluation, and management.

Given the prevalence of bladder dysfunction (i.e., poor compliance or detrusor instability) as a cause of postprostatectomy incontinence, urodynamic studies are essential in the evaluation of such patients. Appropriate management strategies based on the findings of a pertinent history and physical examination, appropriate radiologic studies, and urodynamics optimize the opportunity for successful treatment. Because bladder dysfunction frequently accompanies sphincter insufficiency, bladder dysfunction must be diagnosed and treated effectively before implantation of an artificial urinary sphincter.

Humans↗
PubMed1978

Human erythrocyte 5'-AMP aminohydrolase. Purification and characterization.

Human erythrocyte 5'-AMP aminohydrolase has been obtained using phosphocellulose chromatography and affinity chromatography on a GTP-agarose column to yield a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme has a molecular weight of 285,000, and is comprised of four subunits. Since limited quantities of the homogeneous enzyme were available, the kinetic properties of a nonhomogeneous preparation purified about 20,000-fold over the red blood cell lysate by phosphocellulose chromatography were examined. Like the muscle enzyme, it exhibits a sigmoid AMP saturation curve in the absence of activating monovalent cations; a hyperbolic saturation curve is observed in the presence of 0.15 M KCl. Activation by monovalent cations and ATP, and inhibition by Pi, PPi, GDP, GTP, and 2,3-diphosphoglyceric acid were studied in more detail.

AMP Deaminase↗