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Biomedical subjects

M Rieger

Publications and source records attributed to M Rieger.

At least 73 records · Page 4Linked to original sources
PubMed1994

Complete DNA sequence of yeast chromosome XI.

The complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome XI has been determined. In addition to a compact arrangement of potential protein coding sequences, the 666,448-base-pair sequence has revealed general chromosome patterns; in particular, alternating regional variations in average base composition correlate with variations in local gene density along the chromosome. Significant discrepancies with the previously published genetic map demonstrate the need for using independent physical mapping criteria.

Base Sequence↗
PubMed1994

LDL increases (CA++)i in human endothelial cells and augments thrombin-induced cell signalling.

Low-density lipoproteins (LDLs) stimulate cytosolic calcium ([Ca++]i) in endothelial cells. To elucidate the mechanisms of this response, we compared the effects of low-density lipoprotein (LDL) with those of thrombin, a known endothelial cell agonist. [Ca++]i was measured in cultured endothelial cells from human umbilical veins. Both spectrofluorometry of single cells with fura-2 and confocal microscopy were used. LDL (100 micrograms/ml) led to a rapid increase in [Ca++]i (143 +/- 46 nmol/L to 426 +/- 69 nmd/L; p < 0.05) followed by a sustained plateau phase. Higher concentrations did not increase this response further. Removal of extracellular calcium resulted in a significant decrease of the plateau phase, which remained significantly elevated as compared with baseline values. On the other hand, the initial peak was only slightly altered. Incubation of endothelial cells with thapsigargin (10(-6) mol/L) reduced the initial calcium peak, while the incubation of the cells with pertussis toxin (10(-6) mol/L) for 24 hours abolished the LDL-induced [Ca++]i response together. Down-regulation of LDL receptors by exposing the endothelial cells to high LDL concentrations (500 micrograms/ml) for 24 hours abolished the LDL-induced calcium signal, while preincubation of the cells with acetylated LDL (500 micrograms/ml) did not alter the cellular response to LDL. Visualization of the calcium signal showed a rapid increase in [Ca++]i followed by an increase in the nuclear calcium concentration. The LDL calcium signalling was shorter than that observed with thrombin (0.1 U/ml). Administration of thrombin and LDL together resulted in an increased [Ca++]i response as compared with either substance alone. Our results show that (1) LDL leads to both a release of calcium from intracellular stores and a transmembranous calcium influx, (2) the effect of LDL is dependent on binding to a specific G-protein-coupled receptor, and (3) LDL enhances the activation induced by other agonists.

Calcium↗
PubMed1993

Two computer programs using logit transformation for the analysis of S-shaped curves.

Two BASIC computer programs using logit transformation for the analysis of S-shaped curves are presented. The first program estimates the median effective dose (ED50) of drugs. A maximum likelihood method similar to Finney's algorithm of probit analysis is applied. The second fits S-shaped curves to empirical data which cannot be transformed easily to proportions. Logit transformation proves to be a simple and accurate alternative to probit transformation when computing memory is limited or calculation speed is critical.

Algorithms↗
PubMed1993

[Improved left ventricular ejection fraction directly after transluminal coronary angioplasty].

The purpose of this study was to evaluate if left ventricular ejection fraction (EF) at rest can improve already during the first 4 h after successful transluminal coronary angioplasty (PTCA). Measurements were carried out with the CardioScint LV Function Monitor Version 1.3. Comparison of ejection fraction values evaluated by the CardioScint Monitor revealed a good correlation with usual equilibrium radionuclide ventriculography (n = 28; r = 0.89). Also, intra- and interobserver variability was low (n = 26; r = 0.94 and n = 21; r = 0.92 respectively). Two hundred follow-up-measurements in eight patients over a time period of 4 h revealed a significant decrease of EF from 45 +/- 12% to 39 +/- 18% (p = 0.037) (reference group). This decrease was due to a continuous increase of background activity. The study population consisted of 14 patients with successful PTCA (dilatation from 85 +/- 7 to 34 +/- 9% linear vessel diameter). To evaluate the hemodynamic significance of the coronary lesion, left ventricular ejection fraction was registered during the balloon occlusion of the vessel. After dilatation, 25 EF measurements were carried out in each patient over the following 4 h (350 values). During PTCA, EF decreased from 52 +/- 16 to 37 +/- 9% (p = 0.0027). During the 4-h follow-up EF slightly decreased from 50 +/- 8 to 46 +/- 9% (p = 0.07).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Large-scale synthesis of triple helix forming oligonucleotides using a controlled-pore glass support.

Triple helix forming oligonucleotides that involve purine:purine:pyrimidine interactions are purine-rich oligonucleotides containing 60%-90% G and are usually 25-40 bases long. Synthesis and purification of G-rich oligonucleotides of this length can be difficult even at small scales. Procedures to synthesize these compounds at 200 to 400 mumol scales with high coupling efficiency have been developed using a controlled-pore glass support.

Base Sequence↗
PubMed1992

Comparison of drought resistance among Prunus species from divergent habitats.

Root and shoot characteristics related to drought resistance were compared among cultivated peach (Prunus persica (L.) Batsch.), P. andersonii (Nevada Desert almond), P. besseyi (western sand cherry), P. maritima (beach plum), P. subcordata (Sierra or Pacific plum), and P. tomentosa (Nanking cherry). In all species, shoot characteristics were more closely associated with drought adaptation than root characteristics. The most xeric species, P. andersonii, had the lowest specific leaf area, smallest leaves, highest stomatal conductance (before stress), highest rate of carbon assimilation (A), high root length/leaf area and root weight/leaf area ratios, and the highest leaf nitrogen content on an area basis. Root hydraulic conductivity was similar for all species, indicating a lack of importance of this parameter for drought resistance. During a 5-7 day drought, water use efficiency (WUE) increased as shoot water potentials (Psi) declined to -3.0 to -4.0 MPa for the xeric P. andersonii and P. subcordata, whereas after an initial increase, WUE decreased with declining Psi in the -1.5 to -3.0 MPa range for the more mesic P. maritima, P. persica and P. tomentosa as a result of non-stomatal limitations to A. Carbon assimilation rate decreased linearly with Psi during drought in all species, but the Psi at which A reached zero was not associated with drought adaptation. We conclude that the variation in leaf characteristics among Prunus species could be exploited to improve the drought resistance of commercial cultivars.

Journal Article↗
PubMed1990

Mutational analysis of the Escherichia coli glpFK region with Tn5 mutagenesis and the polymerase chain reaction.

Transposon Tn5 mutagenesis of the Escherichia coli chromosome was used to isolate 21 independent insertion mutations conferring an altered colony color phenotype on MacConkey-glycerol plates. The polymerase chain reaction was used to map 16 of these Tn5 insertions within the glpFK region at 88 min. The most polar Tn5 insertion was shown by nucleotide sequencing to be in the proposed glpF open reading frame. The data suggest that the glpF and glpK genes are in an operon with a bent DNA segment (BENT-6) involved in transcriptional regulation of this operon.

Aquaporins↗
PubMed1990

[Modulation of the biochemical effect of 5-fluorouracil (5-FU) by leucovorin measured by thymidylate synthase activity and nucleoside incorporation into DNA].

Experimental data show that Leucovorin (LCV) can remarkably modify the cytotoxicity of 5-fluorouracil (5-FU). The combined use of both substances results in a more prolonged and pronounced inhibition of DNA-metabolism by inhibiting thymidylate-synthase (TS) activity. This effect is caused by stabilisation of the ternary complex of 5-fluoro-deoxyuridine monophosphate (5-FdUMP), TS and N5,N10-methylenetetrahydrofolate (CH2FH4). The influence of the combined treatment with 5-FU and LCV has been studied on permanently growing human lymphoblastoid cells. Two different methods were used: a) Tritium-release-assay for measurement of TS activity; b) incorporation of 3H-deoxyuridine (3H-dUR) and 3H-thymidine (3H-dTR) into the DNA for determination of the intrinsic nucleoside pools. The results with both methods were similar. Neither with sequential nor with simultaneous application of both substances was it possible to demonstrate a significantly increased substances was it possible to demonstrate a significantly increased inhibition of TS as compared with 5-FU alone. The methods demonstrated are easy to perform and permit the biochemical characterisation of cell populations in which the combination of LCV + 5-FU is not more effective than 5-FU alone. It is suggested that lymphoid cells and normal bone marrow are such populations.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1988

Identification of an orthologous mammalian cytokeratin gene. High degree of intron sequence conservation during evolution of human cytokeratin 10.

Among the human acidic (type I) cytokeratins, components 10 and 11 are especially interesting, as they are under various kinds of expression control. They are synthesized in the suprabasal cell layers of certain stratified epithelia, notably epidermis, in an endogenous differentiation program; they are expressed in certain epithelial tumours but not in others; they can appear de novo in certain pathological situations such as in squamous metaplasias; and their expression in vivo and in vitro is under positive influence of extracellular calcium concentrations and is reduced in the presence of vitamin A or other retinoids. To provide a basis for studies of the various regulatory elements, we have isolated the human gene encoding cytokeratin 10, using a cDNA probe derived from the corresponding bovine gene, and have sequenced the mRNA coding region as well as adjacent regions approximately 1500 bases 5' upstream and 1000 bases 3' downstream. The eight exons encode a polypeptide 59,535 Mr, i.e. somewhat larger than the corresponding bovine and murine proteins. The deduced amino acid sequences display a high degree of homology, which is not restricted to the exons and the 5' and 3' adjacent regions but, surprisingly, is also evident in the seven introns, some of which contain extended sequence elements with 70% identical nucleotides and more, i.e. similar to the homology in the adjacent exons. This exceptionally high level of conservation of intron sequences is discussed in relation to the recently accumulating evidence of the occurrence of intron sequences important in the regulation of the expression of members of other multigene families during development.

Base Sequence↗
PubMed1986

Cloning and expression in Escherichia coli of a synthetic DNA for hirudin, the blood coagulation inhibitor in the leech.

A 235-bp DNA coding for the leech blood coagulation inhibitor, hirudin, was chemically synthesized. The synthesis involved preparation of seven long oligodeoxyribonucleotide pairs which were assembled and cloned using a rapid and simple procedure. More than half of the transformed Escherichia coli cells expressed a biosynthetic polypeptide having biological properties which were very similar to authentic hirudin from the leech Hirudo medicinalis. To achieve efficient expression, we fused the hirudin DNA to a truncated C1 repressor gene of bacteriophage lambda to create a hybrid protein. An additional methionine at the fusion point allowed the active hirudin to be cleaved off by cyanogen bromide.

Animals↗
PubMed1985

Complete sequence of a bovine type I cytokeratin gene: conserved and variable intron positions in genes of polypeptides of the same cytokeratin subfamily.

The complete sequence of a bovine gene encoding an epidermal cytokeratin of mol. wt. 54 500 (No VIb) of the acidic (type I) subfamily is presented, including an extended 5' upstream region. The gene (4377 bp, seven introns) which codes for a representative of the glycine-rich subtype of cytokeratins of this subfamily, is compared with genes coding for: another subtype of type I cytokeratin; a basic (type II) cytokeratin gene; and vimentin, a representative of another intermediate filament (IF) protein class. The positions of the five introns located within the highly homologous alpha-helix-rich rod domain are identical or equivalent, i.e., within the same triplet, in the two cytokeratin I genes. Four of these intron positions are also identical with intron sites in the vimentin gene, and three of these intron positions are identical or similar in the type I and type II cytokeratin subfamilies. On the other hand, the gene organization of both type I cytokeratins differs from that of the type II cytokeratin in the rod region in five intron positions and in the introns located in the carboxy-terminal tail region, with the exception of one position at the rod-tail junction. Remarkably, the two type I cytokeratins also differ from each other in the positions of two introns located at and in the region coding for the hypervariable, carboxy-terminal portion. The introns and the 5' upstream regions of the cytokeratin VIb gene do not display notable sequence homologies with the other IF protein genes, but sequences identical with--or very similar to--certain viral and immunoglobulin enhancers have been identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1985

The respirative breakdown of glucose by Saccharomyces cerevisiae: an assessment of a physiological state.

Cells of Saccharomyces cerevisiae exhibiting respirative glucose metabolism in continuous culture were able to use ethanol as a co-substrate. The ethanol uptake rate was dependent on the residual respirative capacity of the cells. The activities of gluconeogenic enzymes and of malate dehydrogenase were higher in cells degrading glucose respiratively than in cells metabolizing glucose respiro-fermentatively, but were lower than in cells growing on ethanol only. The pattern of distribution of the mitochondrial cytochromes was similar but the differences were less distinct. In synchronously growing cells, the activities of gluconeogenic enzymes and of malate dehydrogenase oscillated, with activities increasing during the budding phase. The increase was preceded by the appearance of ethanol in the culture medium.

Cytochromes↗
PubMed1984

Identification of two types of keratin polypeptides within the acidic cytokeratin subfamily I.

Cytoskeletal filaments of the alpha-keratin type (cytokeratins) are a characteristic of epithelial cells. In diverse mammals (man, cow and rodents) these cytokeratins consist of a family of approximately 20 polypeptides, which may be divided into the more acidic (I) and the more basic (II) subfamilies. These two subfamilies show only limited amino acid sequence homology. In contrast, nucleic acid hybridization experiments and peptide maps have been interpreted to show that polypeptides of the same subfamily share extended sequence homology. We compare two polypeptides of the acidic cytokeratin subfamily, VIb (Mr 54,000) and VII (Mr 50,000), which are co-expressed in large amounts in bovine epidermal keratinocytes. These two epidermal keratins can be distinguished by specific antibodies and show different patterns of expression among several bovine tissues and cultured cells. In addition, they differ in the stability of their complexes with basic keratin polypeptides and in their tryptic peptide maps. The amino acid sequences deduced from the nucleotide sequences of complementary DNA clones containing the 3' ends of the messenger RNAs for these keratins are compared with each other and with available amino acid sequences of human, murine and amphibian epidermal keratins. Bovine keratins VIb and VII share considerable sequence homology in the alpha-helical portion (68% residues identical) but lack significant homology in the extrahelical portion. Bovine keratin VIb shows, in its alpha-helical region, a pronounced sequence homology (88% identity) to the murine epidermal keratin of Mr 59,000. In addition, the non-helical carboxy-terminal regions of both proteins are glycine-rich and contain a canonic sequence GGGSGYGG, which may be repeated several times. Moreover, their mRNAs present a highly conserved stretch of 236 nucleotides containing, in the murine sequence, the end of the coding and all of the non-coding region (81% identical nucleotides). Bovine keratin VII is considerably different from the murine Mr 59,000 keratin but is almost identical to the human cytokeratin number 14 of Mr 50,000, both in the alpha-helical and in the non-alpha-helical regions of the proteins, and the mRNAs of the human and the bovine keratins also display a high homology in their 3' non-coding ends. The results show that in the same species keratins of the same subfamily can differ considerably, whereas equivalent keratin polypeptides of different species are readily identified by characteristic sequence homologies in the alpha-helical and the non-helical regions as well as in the 3' non-coding portions of their mRNAs.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1980

Partial purification and separation of H-2 antigens by free-flow preparative electrophoresis.

The membrane fraction of murine spleen cells was solubilized by autolysis in 0.25% potassium cholate and 3M potassium chloride, and the solubilized membrane components were fractionated by ultrafiltration and preparative free-flow electrophoresis. This procedure yielded partially purified fractions with enriched specific antigenic activities. The H-2Ka and H-2Da antigens were found to possess distinctly different electrophoretic mobilities.

Animals↗