PubMed Health⌕ Search

Biomedical subjects

M Lu

Publications and source records attributed to M Lu.

At least 19 recordsLinked to original sources
PubMed1992

Adenine affects the structure and stability of telomeric sequences.

Adenine occurs in the strand containing repeated G clusters in the telomeric DNA of a variety of organisms, including that of humans. The role of adenine has been investigated by constructing two sets of oligonucleotides each with one, two, or four copies of the telomeric sequence dTTTAGGG together with a control sequence in which T replaces the A residue, dTTTTGGG. Comparison of the stability and spectral properties of these two sequences in the presence of Na+ or K+ affords a basis for defining the role of adenine in these structures. In Na+, the A residue stabilizes the structure formed by each oligomer significantly, presumably by a base-pairing interaction with T. In K+, by contrast, there is little difference in stability. In two- and four-copy oligomers, the A sequence has a different structure from its T analog, as detected by CD spectroscopy. In the presence of either Na+ or K+, the tetraplexes of A and T interact with intercalators.

Adenine↗
PubMed1992

Conformational properties of B-Z junctions in DNA.

The structural consequences of specific base sequences in DNA can exert a strong influence on the function of DNA. It has previously been reported that the presence of multiple B-Z conformational junctions in constructed DNA oligomers results in unusually enhanced electrophoretic gel mobilities of these oligomers [Winkle, S. A., & Sheardy, R. D. (1990) Biochemistry 29, 6514-6521]. In order to investigate this phenomenon further, we designed and synthesized several DNA oligomers capable of pure Z or B-Z junction formation for polyacrylamide gel electrophoresis studies. The results indicate that both pure Z-DNA and polymorphic B-Z-DNA oligomers exhibit unusual gel migratory properties. The results of gel mobility studies in the absence and presence of cobalt hexamine indicate that a B-Z junction corresponds to a stiff bend of the helix axis, with two or more conformers accessible at the junction site. This is a different bend and mechanism than that in oligo(A) tracts.

Base Sequence↗
PubMed1992

Expression cloning and characterization of the canine parietal cell gastrin receptor.

Gastrin is an important stimulant of acid secretion by gastric parietal cells and is structurally related to the peptide hormone cholecystokinin (CCK). The pharmacologic properties of the parietal cell gastrin receptor are very similar to the predominant CCK receptor in the brain, CCK-B. Neither the gastrin nor the CCK-B receptor have been cloned thus far, making it difficult to resolve whether these two receptors are distinct. We have isolated a clone encoding the canine gastrin receptor by screening a parietal cell cDNA expression library using a radioligand-binding strategy. Nucleotide sequence analysis revealed an open reading frame encoding a 453-amino acid protein with seven putative hydrophobic transmembrane domains and significant homology with members of the beta-adrenergic family of G protein-coupled receptors. The expressed recombinant receptor shows the same binding specificity for gastrin/CCK agonists and antagonists as the canine parietal cell receptor. Gastrin-stimulated phosphatidylinositol hydrolysis and intracellular Ca2+ mobilization in COS-7 cells expressing the cloned receptor suggest second-messenger signaling through phospholipase C. Affinity labeling of the expressed receptor in COS-7 cells revealed a protein identical in size to the native parietal cell receptor. Gastrin receptor transcripts were identified by high-stringency RNA blot analysis in both parietal cells and cerebral cortex, suggesting that the gastrin and CCK-B receptors are either highly homologous or identical.

Amino Acid Sequence↗
PubMed1992

Interaction of the dye ethidium bromide with DNA containing guanine repeats.

DNA containing one or more copies of the motifs repeated in telomere sequences has unusual conformational properties. The isolated sequence from the protozoan Oxytricha, dT4G4 has the potential to form tetramers in the presence of sodium or potassium ions. We report here that these tetramers bind ethidium tightly, with an interaction that fulfills several criteria for an intercalative mechanism in the G sequence. By contrast, the 4-fold tandem repeat of this subunit, d(T4G4)4, does not interact specifically with ethidium in the presence of Na+. This difference might have a simple structural basis: the tetramer of dT4G4 forms a stack of four G-quartets in the presence of Na+ or K+, whereas the constraint imposed by the T4 "tethers" in the repeat d(T4G4)4 allows only two layers to form in the presence of Na+. In the presence of sufficient K+, the latter can partially form a four-layer G-quartet structure, which interacts with ethidium. This idea is supported by analysis of a "relaxed" sequence, dT4G4(T7G4)3, which allows formation of four G-quartets and binds ethidium in the presence of Na+ as well as K+. Ethidium (and intercalators generally) should thus be able to retard or inhibit the action of telomerase in the presence of K+.

Animals↗
PubMed1992

Structure and stability of sodium and potassium complexes of dT4G4 and dT4G4T.

The ends of eukaryotic chromosomes contain specialized structures that include DNA with multiple tandem repeats of simple sequences containing clusters of G on one strand, together with proteins which synthesize and bind to these sequences. The unit repeat in the protozoan Oxytricha with the cluster dT4G4 can form structures containing tetrads of guanine residues, referred to G4 DNA, in the presence of metal ions such as Na+ or K+. We show here that, in the presence of Na+, dT4G4 forms a tetramer with parallel strands by means of a UV cross-linking assay. In the presence of K+, two further interactions are observed: at low temperature, higher order complexes are formed, provided the 3' end of the strand is G; a single 3'T inhibits this association in dT4G4T. At high temperature, these complexes dissociate, leading to a tetramer with a different ordered structure that melts only at very high temperatures. These results suggest that the cohesive properties of DNA containing G clusters might depend on associative interactions driven by a free 3'G terminus in the presence of K+, as well as by connecting antiparallel G hairpins as has been postulated.

Circular Dichroism↗
PubMed1992

Thermodynamics of DNA branching.

Branched DNA molecules arise transiently as intermediates in genetic recombination or on extrusion of cruciforms from covalent circular DNA duplexes that contain palindromic sequences. The free energy of these structures relative to normal DNA duplexes is of interest both physically and biologically. Oligonucleotide complexes that can form stable branched structures, DNA junctions, have made it possible to model normally unstable branched states of DNA such as Holliday recombinational intermediates. We present here an evaluation of the free energy of creating four-arm branch points in duplex DNA, using a system of two complementary junctions and four DNA duplexes formed from different combinations of the same set of eight 16-mer strands. The thermodynamics of formation of each branched structure from the matching pair of intact duplexes have been estimated in two experiments. In the first, labeled strands are allowed to partition between duplexes and junctions in a competition assay on polyacrylamide gels. In the second, the heats of forming branched or linear molecules from the component strands have been determined by titration microcalorimetry at several temperatures. Taken together these measurements allow us to determine the standard thermodynamic parameters for the process of creating a branch in an otherwise normal DNA duplex. The free energy for reacting two 16-mer duplexes to yield a four-arm junction in which the branch site is incapable of migrating is + 1.1 (+/- 0.4) kcal mol-1 (at 18 degrees C, 10 mM-Mg2+). Analysis of the distribution of duplex and tetramer products by electrophoresis confirms that the free energy difference between the four duplexes and two junctions is small at this temperature. The associated enthalpy change at 18 degrees C is +27.1 (+/- 1.3) kcal mol-1, while the entropy is +89 (+/- 30) cal K-1 mol-1. The free energy for branching is temperature dependent, with a large unfavorable enthalpy change compensated by a favorable entropy term. Since forming one four-stranded complex from two duplexes should be an entropically unfavorable process, branch formation is likely to be accompanied by significant changes in hydration and ion binding. A significant apparent delta Cp is also observed for the formation of one mole of junction, +0.97 (+/-0.05) kcal deg-1 mol-1.

Base Composition↗
PubMed1992

S1 nuclease hypersensitive sites in an oligopurine/oligopyrimidine DNA from the t(10;14) breakpoint cluster region.

Recurring chromosomal translocations are frequently seen in cancers, especially in leukemias and lymphomas. The genes affected by these chromosomal translocations appear to play an important role in oncogenesis. The mechanism underlying the formation of chromosomal translocation is a subject under extensive study. In chromosomal translocations involving the Ig and TCR loci, complete heptamer-spacer-nonamer signal motifs are usually present at the break of the Ig and TCR genes, indicating the involvement of V-D-J recombinase(s). On the other hand, in only about 50% of the cases signal motif sequences have been found at the break in the other participating chromosome, suggesting that different mechanisms may be involved in the scission of the corresponding chromosome. Here we report the identification of an oligopurine/oligopyrimidine DNA in the t(10;14) breakpoint cluster region associated with T-cell acute lymphoblastic leukemia. S1 nuclease mapping revealed multiple S1 hypersensitive sites in the oligopurine/oligopyrimidine DNA. These data suggest a role for oligopurine/oligopyrimidine sequences (non-B DNA) in the formation of chromosomal translocation.

Base Sequence↗
PubMed1992

A mitochondrial DNA sequence is associated with abnormal pollen development in cytoplasmic male sterile bean plants.

Cytoplasmic male sterility (CMS) in common bean is associated with the presence of a 3-kb unique mitochondrial sequence designated pvs. The pvs sequence encodes at least two open reading frames (297 and 720 bp in length) with portions derived from the chloroplast genome. Fertility restoration by the nuclear restorer gene Fr results in the loss of this transcriptionally active unique region. We examined the effect of CMS (pvs present) and fertility restoration by Fr (pvs absent) on the pattern of pollen development in bean. In the CMS line, pollen aborted in the tetrad stage late in microgametogenesis. Microspores maintained cytoplasmic connections throughout pollen development, indicating aberrant or incomplete cytokinesis. Pollen-specific events associated with pollen abortion and fertility restoration imply that a gametophytic factor or event may be involved in CMS. In situ hybridization experiments suggested that significant reduction or complete loss of the mitochondrial sterility-associated sequence occurred in fertile pollen of F2 populations segregating for fertility. These observations support a model of fertility restoration by the loss of a mitochondrial DNA sequence prior to or during microsporogenesis/gametogenesis.

Amino Acid Sequence↗
PubMed1992

Cryptosporidium infection and diarrhea in rural and urban areas of Jiangsu, People's Republic of China.

Screening of infants and children under age 15 years for Cryptosporidium oocysts in their stools was carried out in the suburb of Xuzhou City and six rural areas of Jiangsu Province. The infection rate varied from 0.7 to 5.06%. Of the total of 5,089 children examined, 89 (1.75%) were oocyst positive. The incidence was evidently higher in the group of children under age 4 years than it was in children from 4 to 15 years (P less than 0.01). Routine blood examination and immunoassay performed on blood samples from some of the infected children indicated that more than half of them had anemia and lower cellular immunity. Diarrhea was the main symptom of cryptosporidiosis. It was intermittent or persistent and was present in 57 of the 89 children positive for Cryptosporidium oocysts, while the other 32 children were asymptomatic carriers. Examination of stool specimens of adult members and domestic animals of about half of the infected families showed that two mothers, one pig, and one dog were positive for Cryptosporidium oocysts.

Adolescent↗
PubMed1992

Development of proliferative retinopathy in NIDDM. A follow-up study of American Indians in Oklahoma.

To determine the incidence of and risk factors for the development of proliferative diabetic retinopathy (PDR) in Oklahoma Indians, we performed a cohort follow-up study of 927 Indians who underwent detailed eye examinations between 1972 and 1980. The mean age of participants was 52 yr with a duration of diabetes of 6.9 yr at baseline. At follow-up, 513 (55.3%) were alive, 407 (43.9%) were deceased, and 7 (0.8%) could not be traced. After a mean follow-up time of 12.7 yr, the overall incidence of PDR among those who survived and who underwent follow-up ophthalmic examinations (354 participants) was 18.6%; 45% of those with background retinopathy at baseline developed PDR. Significant independent predictors of PDR, determined by multivariate analysis, were fasting plasma glucose level, duration of diabetes, plasma cholesterol, systolic blood pressure, and therapeutic regimen. A fasting plasma glucose level greater than or equal to 11.1 mM (200 mg/dl) increased the risk of retinopathy to 3.6 times that for a level less than 7.8 mM (140 mg/dl); 74% of those who had background retinopathy and a baseline fasting glucose greater than or equal to 11.1 mM (200 mg/dl) developed PDR. Over half of all participants with plasma cholesterol levels greater than or equal to 7.8 mM (300 mg/dl) developed PDR in the follow-up interval. Elevated systolic blood pressure was a particularly significant risk factor for those with a long duration of diabetes. Proliferative retinopathy poses a serious health threat to Oklahoma Indians and represents a cause of visual impairment that may be preventable by early diagnosis of PDR and intervention with photocoagulation therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Diabetic retinopathy in Oklahoma Indians with NIDDM. Incidence and risk factors.

OBJECTIVE: To determine the incidence rates and risk factors for development of diabetic retinopathy in Oklahoma Indians. RESEARCH DESIGN AND METHODS: Cohort follow-up study with baseline examination between 1972 and 1980 and follow-up examination between 1987 and 1991. Mean +/- SD follow-up time was 12.8 +/- 1.7 yr. Eleven Indian Health Service facilities (clinics and hospitals) in Oklahoma participated in the study. Study participants were a quasirandom sample of 1012 American Indians (379 men, 633 women) in Oklahoma with NIDDM, 927 of whom received a detailed eye examination at baseline. The mean age of participants was 52 yr with a duration of diabetes of 6.9 yr at baseline. The average quantum of Indian blood was 92% (77% full blood). At follow-up, 515 (55.6%) were alive, 408 (44.0%) were deceased, and 4 (0.4%) could not be traced. Of the living participants, 380 (73.8%) underwent an ophthalmoscopic examination. RESULTS: The incidence of retinopathy among the participants who were free of disease at baseline and who survived the follow-up interval was 72.3%. By multivariate analysis, significant independent predictors of retinopathy recorded at baseline were FPG level, therapeutic regimen, systolic blood pressure, and duration of diabetes. FPG levels > or = 11.1 mM (200 mg/dl) increased the risk of retinopathy 1.7 times that for levels < 7.8 mM (140 mg/dl). Insulin use was associated with a 20% greater incidence. Hypertension was a particularly significant risk factor for those with lower FPG levels. CONCLUSIONS: Given that NIDDM is reaching epidemic proportions in Oklahoma Indians and that most may be afflicted with retinopathy, frequent ophthalmological examinations are clearly indicated for this high-risk population. The role of intervention, namely glycemic and hypertensive control, deserves further study.

Blood Glucose↗
PubMed1992

Genomic organization of the putative human homeobox proto-oncogene HOX-11 (TCL-3) and its endogenous expression in T cells.

The HOX-11 (TCL-3) gene, which is abnormally expressed in the leukemic cells of some patients with T-cell acute lymphoblastic leukemia, is a new member of the homeobox gene family. It is structurally altered by the t(10;14) chromosomal translocation, resulting in head-to-tail juxtaposition of HOX-11 with the T-cell receptor delta-chain gene. In order to understand the normal functions of HOX-11 and its role in T-cell leukemia, we have determined the exon-intron structure of the HOX-11 gene. By using oligonucleotide primers flanking an intron of the HOX-11 gene, we have developed a quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay for the expression of HOX-11. We detected HOX-11 expression in multiple cell lineages including normal T cells and two T-cell lines in which the HOX-11 gene appeared to be unaltered in structure. Our results suggest that deregulation of the endogenous expression of HOX-11 in normal T cells represents an essential step towards the formation of this type of T-cell leukemia.

Amino Acid Sequence↗
PubMed1992

[Pharmacokinetic analysis of enterohepatic circulation of piroxicam in rabbits].

The concentration (c)-time (t) curves of piroxicam showed double peaks following iv 10 mg dose to 4 rabbits. A new mathematical model of enterohepatic circulation was proposed to explain this double-peak phenomenon and showed good agreement with data. This model provides not only the common pharmacokinetic parameters: T1/2 = 1.12 +/- 0.32 h, V1 = 0.64 +/- 0.12 L, AUC = 34.7 +/- 7.8 micrograms.h-1.ml-1, but also the parameters of enterohepatic circulation of piroxicam: the cycling amount of drug Db = 3.9 +/- 1.4 mg, reabsorption fraction Fb = 0.50 +/- 0.04, reabsorption rate constant Ka = 2.55 +/- 0.50 h-1. It is indicated in this study that enterohepatic circulation results in a 20% average increase of the effective amount of piroxicam.

Animals↗
PubMed1991

Drug binding to a DNA BZ molecule: analysis by chemical footprinting.

The polymorphism in a DNA 16-mer (designated BZ-II) has been investigated by means of circular dichroism (CD) spectroscopy and chemical footprinting. CD spectra indicate that, in low salt, the oligomer is fully right-handed whereas, in high salt, it possesses a B-Z conformational junction: half of the duplex is right-handed while the other half is left-handed. Treatment of BZ-II with diethyl pyrocarbonate (DEPC) confirms the existence of a left-handed segment of the duplex in high salt: enhanced DEPC scission occurs at the G residues in the alternating CG sequence. The scission patterns of the upper and lower strands in BZ-II by the reactive chemical probe MPE.Fe(II), and the antitumor antibiotics dynemicin and Fe-(II).bleomycin, are different under low salt conditions. The 3'-terminal region of both upper and lower strands and the middle region of the upper strand of BZ-II are preferential cleavage sites in low salt. This result suggests that the methylated cytosines or the alternating CG domain in the molecule perturbs the DNA structure. Under high salt conditions, the reactivity of the Z-DNA segment of BZ-II for MPE.Fe(II) and Fe(II).bleomycin is dramatically enhanced, while it is reduced in the case of dynemicin. Excess propidium (PI) eliminates preferential cleavage by each of these chemical probes in high salt conditions. This is due in part to conversion of the BZ-DNA molecule into B-DNA, as is seen by a DEPC modification experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Anthraquinones↗
PubMed1991

A novel human homeobox gene lies at the chromosome 10 breakpoint in lymphoid neoplasias with chromosomal translocation t(10;14).

The translocation t(10;14)(q24;q11) is an acquired change seen in 4% to 7% of T-cell acute lymphoblastic leukemias (T-ALL). We previously demonstrated that the translocation juxtaposes the T-cell receptor (TCR) delta-chain gene in chromosome 14q11 with a novel region in chromosome 10q24 and is likely catalyzed by recombinases normally involved in the generation of immunoglobulin and TCR diversity. We now present the sequence of a gene on chromosome 10 that lies immediately telomeric of the breakpoints in nine new ALL patients with acquired rearrangements in 10q24. The gene is a novel human homeobox gene and is expressed in leukemic cells from ALL patients with rearrangements in a defined chromosome 10 breakpoint cluster region, but not in other adult tissues or cell lines. This new gene has been designated HOX11. Our results strongly support a role for homeobox genes in oncogenesis and may represent the first example of a human cancer in which deregulated expression of an unaltered homeobox gene is involved in tumorigenesis.

Amino Acid Sequence↗
PubMed1991

Recognition of the highly conserved GTPase center of 23 S ribosomal RNA by ribosomal protein L11 and the antibiotic thiostrepton.

The antibiotic thiostrepton, a thiazole-containing peptide, inhibits translation and ribosomal GTPase activity by binding directly to a limited and highly conserved region of the large subunit ribosomal RNA termed the GTPase center. We have previously used a filter binding assay to examine the binding of ribosomal protein L11 to a set of ribosomal RNA fragments encompassing the Escherichia coli GTPase center sequence. We show here that thiostrepton binding to the same RNA fragments can also be detected in a filter binding assay. Binding is relatively independent of monovalent salt concentration and temperature but requires a minimum Mg2+ concentration of about 0.5 mM. To help determine the RNA features recognized by L11 and thiostrepton, a set of over 40 RNA sequence variants was prepared which, taken together, change every nucleotide within the 1051 to 1108 recognition domain while preserving the known secondary structure of the RNA. Binding constants for L11 and thiostrepton interaction with these RNAs were measured. Only a small number of sequence variants had more than fivefold effects on L11 binding affinities, and most of these were clustered around a junction of helical segments. These same mutants had similar effects on thiostrepton binding, but more than half of the other sequence changes substantially reduced thiostrepton binding. On the basis of these data and chemical modification studies of this RNA domain in the literature, we propose that L11 makes few, if any, contacts with RNA bases, but recognizes the three-dimensional conformation of the RNA backbone. We also argue from the data that thiostrepton is probably sensitive to small changes in RNA conformation. The results are discussed in terms of a model in which conformational flexibility of the GTPase center RNA is functionally important during the ribosome elongation cycle.

Base Composition↗