Biomedical subjects

D Lohr

Publications and source records attributed to D Lohr.

At least 37 records · Page 2Linked to original sources

PubMed1995

GAL4/GAL80-dependent nucleosome disruption/deposition on the upstream regions of the yeast GAL1-10 and GAL80 genes.

Metabolic reactivation (incubating spheroplasts with galactose and casamino acids) causes disruption of nucleosomes from the upstream regions of the yeast GAL1, GAL10, and GAL80 genes. The disruption is specific. It depends on the transcription activator Gal4; it only occurs in galactose-reactivated chromatin from galactose-grown cells; it only affects upstream region, gene-proximal nucleosomes. Due to this specificity and because some of the same regions have shown induction-dependent changes by in vivo analyses, we suggest that the nucleosome-disrupted structure produced by reactivation is the authentic chromatin structure for these regions under conditions of galactose-induced GAL1-10 and GAL80 expression. It is necessary to carry out a spheroplast reactivation treatment in order to observe this disrupted structure in nuclear chromatin because nucleosomes are redeposited onto these regions during the preliminary steps of nuclear isolation (cell harvest/spheroplast preparation) probably in response to the nonphysiological conditions associated with these steps. However, during the same isolation procedures in cells lacking Gal80 protein, there is no nucleosome deposition on these regions, and the in vivo disrupted structure remains present in the nuclear chromatin. Therefore, the nucleosome deposition process that operates in wild-type cells is dependent on Gal80 protein, defining another activity of this negative regulator.

Chromatin↗

PubMed1995

Transcriptional regulation in the yeast GAL gene family: a complex genetic network.

Regulation of the GAL structural genes in the yeast Saccharomyces cerevisiae is implemented by the products of GAL-specific (GAL4, GAL80, GAL3) and general (GAL11, SWI1, 2, 3, SNF5, 6, numerous glucose repression) genes. Recent work has 1) yielded significant new insights on the DNA binding and transcription activation/Gal80 protein binding functions of the Gal4 activator protein, 2) described the characterization of purified Gal4 protein-Gal80 protein complexes, 3) deconvoluted the multiple and complex glucose repression pathways acting on GAL genes, 4) suggested a new mechanism for the Gal3 protein-mediated induction of GAL structural gene expression, 5) introduced Gal1 protein, a structural gene product, into the regulation scheme, and 6) extended our already substantial understanding of GAL regulatory gene control. The mechanisms which control structural and regulatory gene expression in the GAL family are compared and GAL structural/regulatory gene chromatin structure is discussed.

Chromatin↗

PubMed1993

Chromatin structure and regulation of the eukaryotic regulatory gene GAL80.

The chromatin structure around the 5' end of the yeast regulatory gene GAL80 has been determined. The chromatin organization is very similar to that on the 5' regions of the GAL1-10 structural genes: a constitutive hypersensitive region containing the upstream activating sequence (UAS) element, and nucleosomes around this hypersensitive region. The downstream nucleosome, which is a positioned nucleosome, covers the TATA and transcription start sites. The nucleosome upstream of the hypersensitive region undergoes significant change when cells are grown in galactose, where GAL80 gene expression is induced to maximal levels. The change may be related to the induction process. GAL4 protein binds strongly to the GAL80 UAS in galactose-grown cells, less strongly in glycerol-grown cells, and not at all in glucose-grown cells. These data and published gene expression data are used to develop a model for the regulation of the GAL80 regulatory gene.

Chromatin↗

PubMed1993

Assembly and structural properties of subsaturated chromatin arrays.

Nucleosomes have been reconstituted onto dodecameric repeats of a 208-base pair nucleosome positioning sequence at various subsaturating molar ratios of histone octamer to DNA repeat (r). These reconstitutes have been characterized with respect to lattice site occupancy distributions, nucleosome positioning, chromatin folding, and histone octamer dissociation. Reconstitution at 0.3 < or = r < or = 0.9 produces subsaturated chromatin templates with distinct compositional limits, n +/- 2 nucleosomes, where n is the average number of nucleosomes present on the template at that r value. Nucleosomes on subsaturated arrays occupy the same set of specific positions within the repeat unit as they do on saturated templates, with only very slight differences in the relative frequency of occupation of the various positions. The nucleosomes on very subsaturated templates, i.e. r < or = 0.5, are generally spread out. However, some nucleosome clustering is observed on these very subsaturated templates. These results indicate that assembly of nucleosomes onto this DNA lattice is not a strongly cooperative process. In 200 mM NaCl, subsaturated reconstitutes exhibit reduced levels of folding and histone octamer dissociation compared with saturated arrays. These results provide a framework for understanding the structural features of regions of chromatin partially depleted of nucleosomes.

Animals↗

PubMed1993

[Changes in central hemodynamics and peripheral circulation in pregnancy].

Systemic blood pressure, stroke volume, systolic time intervals (measured via impedance cardiography), rheological properties of blood (hematocrit, plasma viscosity and erythrocyte aggregation) and peripheral flow conditions (measured via occlusive impedance plethysmography) were assessed longitudinally in 21 nonpregnant women and in 49 patients from 5th to 41st week of gestation and 4 to 9 days postpartum. Measurements were taken in the left lateral position. The data showed, that dz/dt, stroke volume and cardiac index rose until the 30th week of gestation and decreased throughout the rest of pregnancy. The same changes were observed in the data on diastolic pressure and Heather Index. Peripheral resistance fell during the first trimester and then increased notably throughout the following time of pregnancy. The systolic time intervals become longer in the last trimester of pregnancy, but were characterised by a markedly shortened left ventricular ejection time (LVET). The reduction of stroke volume in the last trimester is due to diminished venous return or venous outflow by obstruction of the inferior vena cava or by abnormalities in the left ventricular function and/or impaired rheological properties of the blood.

Adult↗

PubMed1991

The mechanism of nucleosome assembly onto oligomers of the sea urchin 5 S DNA positioning sequence.

We have used a model system composed of tandem repeats of Lytechinus variegatus 5 S rDNA (Simpson, R. T., Thoma, F., and Brubaker, J. M. (1985) Cell 42, 799-808) reconstituted into chromatin with chicken erythrocyte core histones to investigate the mechanism of chromatin assembly. Nucleosomes are assembled onto the DNA template by mixing histone octamers and DNA in 2 M NaCl followed by stepwise dialysis into very low ionic strength buffer over a 24-h period. By 1.0 M NaCl, a defined intermediate composed of arrays of H3.H4 tetramers has formed, as shown by analytical and preparative ultracentrifugation. Digestion with methidium propyl EDTA.Fe(II) indicates that these tetramers are spaced at 207 base pair intervals, i.e. one/repeat length of the DNA positioning sequence. In 0.8 M NaCl, some H2A.H2B has become associated with the H3.H4 tetramers and DNA. Surprisingly, under these conditions DNA is protected from methidium propyl EDTA.Fe(II) digestion almost as well as in the complete nucleosome, even though these structures are quite deficient in H2A.H2B. By 0.6 M NaCl, nucleosome assembly is complete, and the MPE digestion pattern is indistinguishable from that observed for oligonucleosomes at very low ionic strength. Below 0.6 M NaCl, the oligonucleosomes are involved in various salt-dependent conformational equilibria: at approximately 0.6 M, a 15% reduction in S20,w that mimics a conformational change observed previously with nucleosome core particles; at and above 0.1 M, folding into a more compact structure(s); at and above 0.1 M NaCl, a reaction involving varying amounts of dissociation of histone octamers from a small fraction of the DNA templates. In low ionic strength buffer (less than 1 mM NaCl), oligonucleosomes are present as fully loaded templates in the extended beads-on-a-string structure.

Animals↗

PubMed1989

The yeast GAL1-10 UAS region readily accepts nucleosomes in vitro.

To test if the absence of nucleosomes on the UAS region of the yeast GAL1-10 genes in vivo could be due to a low inherent affinity of this DNA for histones, DNA fragments containing the UAS and various amounts of flanking DNA were reconstituted into chromatin. Restriction enzyme and DNase I digestion analyses show that DNA in the UAS becomes protected against digestion in the reconstitutes. Thus, nucleosomes can assemble on the UAS region in vitro. The level of protection of the UAS and of the flanking DNA regions is comparable and remains so at various levels of nucleosome loading, suggesting that the UAS DNA has no tendency to exclude nucleosomes. In fact, DNase I results suggest that the UAS elements themselves preferentially bind histones.

Animals↗

PubMed1988

Relationship between mitochondrial lipid peroxidation and alpha-tocopherol levels in the guinea-pig adrenal cortex.

Lipid peroxidation in mitochondria from the functionally distinct inner (zona reticularis) and outer (zona fasciculata + zona glomerulosa) zones of the guinea-pig adrenal cortex was investigated. Ferrous ion (Fe2+)-induced lipid peroxidation was far greater in inner than outer zone mitochondria. Ascorbic acid similarly initiated lipid peroxidation to a greater extent in inner zone mitochondrial preparations. Differences in the unsaturated fatty acid content of inner and outer zone mitochondria could not account for the regional differences in lipid peroxidation. Total fatty acid concentrations were greater in the outer than in the inner zone, and the relative amounts of each fatty acid were similar in the two zones. However, mitochondrial concentrations of alpha-tocopherol, an antioxidant known to inhibit lipid peroxidation, were approx. 5-times greater in the outer than inner zone. The results demonstrate that there are regional differences in mitochondrial lipid peroxidation in the adrenal cortex which may be attributable to differences in alpha-tocopherol content. Thus, alpha-tocopherol may serve to protect outer zone mitochondrial enzymes from the consequences of lipid peroxidation and thereby contribute to some of the functional differences between the zones of the adrenal cortex.

Adrenal Cortex↗

PubMed1988

Structure of the chromosomal copy of yeast ARS1.

We have used deoxyribonuclease I (DNase I) and methidium-propyl-EDTA.Fe(II) digestion to characterize the chromosomal structure of the single-copy autonomously replicating sequence ARS1. The major feature of this chromatin is a region of strong hypersensitivity to both cleavage agents. The hypersensitive region contains most of the DNA sequences which have been suggested by in vitro mutagenesis studies [Celniker, S., Sweder, K., Srienc, F., Bailey, J., & Campbell, J. (1984) Mol. Cell. Biol. 4, 2455-2466] to be important in ARS function. It lies at the downstream end of the TRP1 gene. A chromosomal DNase I footprinting analysis was carried out on the hypersensitive region. These data give direct evidence for several localized DNA/protein contacts within the hypersensitive region. The most prominent of these chromatin-dependent contacts is located on the functionally most important 11 base pairs of ARS DNA. On the TRP1 side of the hypersensitive region, there are positioned nucleosomes. On the other side of the hypersensitive region, there is a complex (and possibly heterogeneous) structure.

Chemical Phenomena↗

PubMed1987

The regulatory protein GAL80 is a determinant of the chromatin structure of the yeast GAL1-10 control region.

Chromatin in the regions between the upstream activator sequence and the 5' ends of the yeast GAL1 and GAL10 genes has been analyzed by DNase I chromosomal footprinting and micrococcal nuclease digestion using the indirect end-labeling approach. Comparison of wild type chromatin digests to naked DNA digests shows that there are specific regions of these upstream sequences which are strongly protected in chromatin. Comparison to chromatin digests from cells disrupted for the positive regulatory gene, GAL4, or the negative regulatory gene, GAL80, and thus lacking GAL4 or GAL80 function, shows that these regions of protection in wild type chromatin are GAL80-dependent but not GAL4-dependent. The protected regions include DNA lying on (GAL10) or near (GAL1) the respective TATA boxes. These protections are present in both noninduced and induced cells. Both DNA strands are equally protected. Upstream of GAL1 there is a second protected region. This protection shows considerable expression and strand dependence. These observations provide the first evidence that the GAL80 function influences chromatin structure and suggest possible mechanisms by which GAL80 modulates the GAL1 and 10 promoters in induced cells. Micrococcal nuclease digests also suggest a role for GAL80 in a distinctive higher order organization of the intergenic region, perhaps involving multiprotein complexes.

Chromatin↗

PubMed1987

Calcified renal masses.

A review of the literature and the University of Kentucky Medical Center/Lexington Veterans Administration Medical Center experience regarding calcification of renal masses was undertaken. Twenty per cent of calcified renal masses cannot be easily characterized by CT scan as malignant or benign and are indeterminate. These lesions must be followed closely with follow-up CT scanning or undergo surgical exploration, as 40 per cent may be malignant.

Calcinosis↗

PubMed1986

The salt dependence of chicken and yeast chromatin structure. Effects on internucleosomal organization and relation to active chromatin.

The ionic strength dependences of yeast and chicken erythrocyte chromatin structure have been examined by analysis of nuclear DNase I and Staphylococcal nuclease digestions done under various salt and divalent cation concentrations. The basic features of yeast DNase I profiles (intracore/intercore patterns and their 5-base pair offset) remain present under all conditions tested. However, there are changes in specific parts of the patterns. In very low salt, the intercore DNase I pattern is enhanced; even very small intercore bands can be detected. Staphylococcal nuclease intracore cleavage becomes prominent. Increasing salt enhances the large DNase I intracore bands and the frequency of spacer cleavage for both nucleases. Thus, yeast has a salt-dependent higher order structure: a chromatin fiber with a prominent spacer/core distinction in (physiological) salt; a fiber with a decreased distinction between spacer and core, i.e. a more uniform fiber, in very low salt. The salt-dependent bulk changes resemble single gene chromatin changes during gene expression and may provide a model for that process. Above bands 16.5-17.5, chicken and yeast intercore patterns are coincident. Thus, at least a fraction of chicken chromatin has discrete length spacers like yeast does. This fraction may be significant, for the prominence of the intercore pattern, and hence the apparent abundance of discrete spacers, can be significantly enhanced by digestion in very low salt. The major differences between the two chromatins are in the intracore/intercore transition region: the region is larger and more complex in chicken; ionic strength changes affect the chicken transition region more strongly. Since this region of the profile corresponds to digestion near the ends of the core, that part of the nucleosome must differ in structure and in conformational flexibility in the two chromatins.

Animals↗

PubMed1985

The relationship of regulatory proteins and DNase I hypersensitive sites in the yeast GAL1-10 genes.

We have used yeast strains containing a disrupted positive (GAL4) and/or a disrupted negative (GAL80) regulatory gene to investigate the relationship of these regulatory proteins to the hypersensitive sites upstream of their target genes, GAL1-10. We find that neither of these regulatory proteins is required for the formation of the hypersensitive region. There is positive regulatory protein (dependent) binding to a portion of the hypersensitive region when GAL1 and 10 are expressed. However, similar binding can also occur under conditions in which the genes are not expressed. Thus, such binding is necessary but not sufficient for expression of GAL1 and 10 and control of GAL1-10 expression must also include processes which occur subsequent to GAL4/DNA binding. The negative regulatory protein GAL80 plays a significant role in these processes.

Binding Sites↗

PubMed1984

Organization of the GAL1-GAL10 intergenic control region chromatin.

A defined, "far upstream" promoter element, the Upstream Activator Sequence (UAS), which mediates the galactose dependent induction of expression of the GAL10 gene in yeast, is the locus of an anomalous, mainly expression independent chromatin structure. The UAS chromatin shows three symmetrical DNase I hypersensitive sites in brief digests, a loss of the 10 bp DNase I ladder pattern in more extensive digests and an enhanced staphylococcal nuclease sensitivity. This anomalous structure is confined to a small region of the UAS. The surrounding chromatin, including the TATA box regions shows a more typical, but expression dependent nucleoprotein, probably nucleosomal, organization. Such an arrangement may be a common feature of eukaryotic genes.

Base Sequence↗

PubMed1983

The chromatin structure of an actively expressed, single copy yeast gene.

When the yeast galactokinase gene is not active (repressed, not expressed, quiescent), there is an exceptionally regular nucleosome array on coding sequence galactokinase chromatin, as shown by both denaturing and non-denaturing gel analysis of staphylococcal nuclease digests. Expression of the gene results in a limited smearing of the nucleosome repeat peaks and an increase in interpeak DNA, appearing as a regular ladder of DNA bands on denaturing gels. On non-denaturing gels the pattern is more complex and molecular weight dependent. These data suggest an increase in intracore particle DNA accessibility, allowing staphylococcal nuclease to digest throughout the nucleosome in expressed chromatin. Comparison to bulk chromatin and to an operationally inactive gene (35S rDNA) show that the alteration is specific to expressed chromatin. In contrast, DNase I shows no differences in the digestion of the gene specific chromatin in expressed or inactive states.

Base Sequence↗

PubMed1983

A protected region upstream and limited nucleosomal positioning downstream of the transcription initiation region of the yeast 35S ribosomal gene.

To locate nucleosome positions around the transcription initiation site of 35S rDNA in yeast, single and double cleavage site data for staphylococcal nuclease and single cleavage site data for DNase I were obtained by methods involving some modifications of the usual indirect end-labeling procedure. Results show that immediately upstream of the initiation site there is an approximately 225 base pair (bp) stretch of chromatin which is quite resistant to nuclease digestion. The nucleosomal domain begins on the coding sequences, at the downstream end of the resistant region, with the major locus 30 bp and a minor locus 5 bp downstream of the initiation site in growing cells. The location of the major locus is corroborated by analysis within the coding sequences, although results within the gene are less convincing because of a strong similarity of chromatin and naked DNA digestion profiles. The staphylococcal nuclease cleavage maps were tested by their ability to reproduce chromatin digest profiles and to explain the presence or absence, depending on which parts of the region were used as probes, of specific bands within the pattern. The site of the major upstream locus of the nucleosomal domain differs in growing and stationary cells. This shift changes the accessibility of approximately 25 bp of DNA and may be associated with the expression of these genes.

Base Composition↗

PubMed1983

In vitro initiation and termination of ribosomal RNA transcription in isolated yeast nuclei.

Using the Hg-agarose affinity chromatography/gamma-sulfhydryl nucleotide technique of Reeve, et al. (Reeve, A., Smith, M., Pigiet, V., and Huang, R. (1977) Biochemistry 10, 4464-4469) and high resolution electrotransfer of DNA electrophoretograms to diazobenzyloxymethyl paper, we have analyzed the transcription from the 5 S and 35 S ribosomal RNA genes in isolated yeast nuclei. In vitro initiation from these complex gene loci exhibits the same fidelities as in vivo with respect to initiating nucleotide, polymerase activity, and initiating and terminating region of DNA template. The efficiency of the experimental approach is enhanced by the use of RNase-deficient yeast strains. Thus, this system can be used to study structural aspects affecting transcription at these loci.

Cell Nucleus↗

PubMed1983

Chromatin structure differs between coding and upstream flanking sequences of the yeast 35S ribosomal genes.

Staphylococcal nuclease (EC 3.1.4.7) and DNase I (EC 3.1.4.5) digestion analysis of the nuclear chromatin structure of the yeast 35S rDNA gene shows the presence of typical and homogeneous nucleosome patterns across the coding sequence. These nucleosomal patterns change abruptly, around the site of transcription initiation and upstream in the 5'-flanking sequences, to a unique pattern with both nucleosomal and nonnucleosomal character. The mix arises, at least partly, from heterogeneity within the population of upstream regions; some regions are nucleosomal, but the majority are nonnucleosomal. The nonnucleosomal set of upstream regions appears to be nucleoprotein associated and, in fact, may be an altered nucleosome structure rather than totally restructured. The abruptness of the transition from nucleosome to other structure suggests restricted nucleosome locations in the region around the transcription initiation site of this gene.

Base Sequence↗