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Biomedical subjects

J H White

Publications and source records attributed to J H White.

At least 19 recordsLinked to original sources
PubMed1992

Closed circular DNA as a probe for protein-induced structural changes.

Biological systems are replete with examples of DNA formed into a closed loop structure, either alone or in close association with proteins. Such closed circular DNA molecules are subject to a topological constraint that modifies, often in a major way, the structure and reactivity of the DNA. The topological constraint also permits closed circular DNAs to be used as analytical tools to learn about the structure of DNA-protein complexes.

DNA Probes↗
PubMed1991

DNA polymerase delta: gene sequences from Plasmodium falciparum indicate that this enzyme is more highly conserved than DNA polymerase alpha.

Genes encoding proteins homologous to the catalytic subunits of DNA polymerase alpha and delta have been cloned from the human malaria parasite Plasmodium falciparum. These are among the first cellular replicative DNA polymerase genes to be cloned and their sequences allow us to make new statements about the relative degrees of conservation of these two enzymes. The most important finding was that P. falciparum Pol delta showed considerable homology to the only other Pol delta enzyme for which published sequence is available, that of S. cerevisiae, displaying an overall amino acid identity of 45% and identity over a highly conserved central region of 59%. In contrast, the level of identity shown over the equivalent central region of Pol alpha between the P. falciparum and S. cerevisiae sequences is only 32%. The sequence data also allowed us to examine the degree of conservation in putative exonuclease domains of Pol delta. The Pol delta gene of P. falciparum maps to chromosome 10 and evidence is presented for the presence of different sized Pol delta mRNA's in the asexual and sexual erythrocytic stages of parasite development.

Amino Acid Sequence↗
PubMed1991

A formula for the average number of knot interlinks caused by type 2 topoisomerase action.

During the double-stranded passage that takes place because of the topoisomerase action, a plectonemically interwound DNA often becomes knotted. In this process, a portion of the substrate supercoils are converted into interlinks that contribute to the topology of the knot formed. In this appendix, an approximate formula is derived for the average number of these interlinks in terms of the number of supercoils and branches in the substrate. This will give an indication of the complexity of the average knot obtained. When two regions of DNA come together before passage, the substrate is divided into two domains in essentially the same way as intramolecular recombination divides the substrate into two domains (Boles, T. C., White, J. H., and Cozzarelli, N. R. (1990) J. Mol. Biol. 213, 931-951). Nodes formed between DNA segments from different domains are called interdomainal.

DNA Topoisomerases, Type II↗
PubMed1991

Evidence for a factor required for transcriptional stimulation by the chimeric acidic activator GAL-VP16 in HeLa cell extracts.

We provide biochemical evidence for the existence of a transcriptional intermediary factor (TIF) in HeLa whole-cell extracts (WCE) that is distinct from the basic transcription factors and that is required for transcriptional stimulation by the chimeric acidic activator GAL-VP16. We have fractionated HeLa WCE by heparin-agarose chromatography. Of transcriptionally active fractions eluting in a step between 0.24 and 0.6 M KCl, the initial fractions are refractory to GAL-VP16 stimulation, whereas subsequent fractions are strongly stimulated by the activator. Aliquots of GAL-VP16-responsive fractions efficiently complement refractory fractions for transcriptional stimulation. Aliquots of responsive fractions are also far more efficient than those of refractory fractions in overcoming transcriptional inhibition that is brought about by high concentrations of GAL-VP16. Experiments performed with heat-treated WCE support the idea that HeLa cells contain a TIF that is essential for GAL-VP16 stimulation, but that is not required for basal transcription. Addition of recombinant yeast or human transcription factor TFIID (rTFIIDY and rTFIIDH, respectively) to a WCE heated at 48 degrees C for 15 min restores basal transcription, but in neither case is the reconstituted system activated by GAL-VP16. However, a 45 degrees C heat-treated WCE reconstituted with either rTFIIDH or rTFIIDY is stimulated by GAL-VP16, suggesting that a HeLa TIF can be selectively inactivated by heating at 48 degrees C, but not at 45 degrees C. Interestingly, a TFIID fraction partially purified from HeLa cell extracts, but not rTFIIDH, efficiently relieves transcriptional inhibition by GAL-VP16, suggesting that there may be an association between TIF(s) and TFIID and, moreover, that TIF(s) may be the direct target of the acidic domain of GAL-VP16. In summary, our results support the existence of a TIF that is not essential for basal transcription but that is required to mediate the stimulatory activity of the acidic activator GAL-VP16.

Biological Factors↗
PubMed1991

The yeast DNA ligase gene CDC9 is controlled by six orientation specific upstream activating sequences that respond to cellular proliferation but which alone cannot mediate cell cycle regulation.

By fusing the CDC9 structural gene to the PGK upstream sequences and the CDC9 upstream to lacZ, we showed that the cell cycle expression of CDC9 is largely due to transcriptional regulation. To investigate the role of six ATGATT upstream repeats in CDC9 regulation, synthetic copies of the sequence were attached to a heterologous gene. The repeats stimulated transcription strongly and additively, but, unlike conventional yeast UAS elements, only when present in one orientation. Transcription driven by the repeats declines in cells held at START of the cell cycle or in stationary phase, as occurs with CDC9. However, the repeats by themselves cannot impart cell cycle regulation to a heterologous gene. CDC9 may therefore be controlled by an activating system operating through the repeats that is sensitive to cellular proliferation and a separate mechanism that governs the periodic expression in the cell cycle.

Base Sequence↗
PubMed1991

Feminism, eating, and mental health.

Eating disorders are prevalent health problems for women today. The traditional biomedical or psychiatric approaches offer a narrow perspective of the problem, its courses, and its treatment. Analyzing disordered eating from a feminist perspective, this article discusses cultural, political, and social phenomena that have had a significant impact on the development of these disorders. Parallels of eating disorders and other women's mental illnesses and the medicalization of their symptoms is explored. A "new view" of disordered eating in women is proposed that can be advanced only through feminist research.

Body Image↗
PubMed1991

Analysis of the response of Saccharomyces cerevisiae cells to Kluyveromyces lactis toxin.

The response of Saccharomyces cerevisiae cells to the toxin produced by certain strains of Kluyveromyces lactis was studied. The toxin caused an arrest of sensitive cells in the unbudded (G1) phase of the cell cycle, consistent with the accumulation of cells with an unreplicated (G1) content of DNA in treated populations. However, toxin-treated cells were not proficient for mating. The effects of the toxin were dependent on its continuous presence for over an hour and removal of cells into fresh medium at earlier times prevented inhibition. Following toxin treatment, cells increased in volume and continued to synthesize protein and RNA, suggesting that they were able to continue growth in the absence of division. However, several lines of evidence suggested that the toxin does not simply block proliferation in G1, but that another continuous or post-G1 event is also affected. Possible models to explain these observations are discussed.

DNA Replication↗
PubMed1990

Structure of plectonemically supercoiled DNA.

Using electron microscopy and topological methods, we have deduced an average structure for negatively supercoiled circular DNA in solution. Our data suggest that DNA has a branched plectonemic (interwound) form over the range of supercoiling tested. The length of the superhelix axis is constant at 41% of the DNA length, whereas the superhelix radius decreases essentially hyperbolically as supercoiling increases. The number of supercoils is 89% of the linking deficit. Both writhe and twist change with supercoiling, but the ratio of the change in writhe to the change in twist is fixed at 2.6:1. The extent of branching of the superhelix axis is proportional to the length of the plasmid, but is insensitive to superhelix density. The relationship between DNA flexibility constants for twisting and bending calculated using our structural data is similar to that deduced from previous studies. The extended thin form of plectonemically supercoiled DNA offers little compaction for cellular packaging, but promotes interaction between cis-acting sequence elements that may be distant in primary structure. We discuss additional biological implications of our structural data.

DNA, Superhelical↗
PubMed1990

An immunodominant murine lymphoma cell surface heterodimer marks thymic progenitor subsets.

mAb 1C11 was raised against the cells of retrovirus-negative, radiation-induced thymomas of C57BL/Ka mice. MAb 1C11 binds to radiation- and RadLV-induced C57BL/Ka lymphomas, to lymphomas of other mouse strains and to B-lineage tumors. The 1C11 Ag is expressed on a subpopulation of normal thymocytes that is enriched in immature cells. After fractionated x-irradiation, this percentage increases gradually during the preleukemic period, hence mAb 1C11 appears to identify a transformation-related cell surface molecule. This conclusion is supported by experiments demonstrating that flow microfluorimetry-sorted, 1C11-expressing preleukemic thymocytes progress rapidly to full neoplasia following intrathymic injection, whereas nonexpressing cells do not. Most of day-14 fetal thymocytes are as strongly positive as thymic lymphomas for the 1C11 Ag whereas Ag-activated T cell lines express moderate levels. Multiparameter flow microfluorimetry analysis shows that 1C11 is expressed predominantly on CD3-/lo thymic blast cells of three phenotypically defined subsets: CD4-8-, CD4-8+, and CD4+8+, all of which contain thymic progenitors. By immunohistochemical staining, the Ag is also found in association with epithelial cells on a variety of normal, nonlymphoid tissue, but is not detectable on heart tissue. The 1C11 antibody immunoprecipitates a disulfide-linked heterodimeric protein of 85/37 kDa and the antigenic determinant is located on the H chain of the molecule. When analyzed by SDS-PAGE under nonreducing conditions, the molecule exists as a 130-kDa protein. Enzymatic digestion of the heterodimer indicates that the H chain, but not the L chain, has at least three N-linked glycosylation sites. We propose that this novel cell surface glycoprotein may be associated with processes of differentiation and lymphomagenesis.

Animals↗
PubMed1990

Synergistic activation of transcription by the human estrogen receptor bound to tandem responsive elements.

The synergistic action of the human estrogen receptor (hER) has been investigated using minimal promoters containing a TATA region and one or two estrogen responsive elements (EREs). We find that paired perfectly palindromic EREs act additively and independently of their relative spacing when positioned close to the TATA box. However, when moved 175 bp further upstream, perfectly palindromic EREs act synergistically and in a stereoalignment-dependent manner. Less efficient imperfectly palindromic EREs display a stereoalignment-dependent synergism even when positioned close to the TATA box. Analysis of binding in vitro of the hER to perfectly or imperfectly palindromic EREs by gel retardation and nitrocellulose filter binding assays does not provide any evidence for cooperative DNA binding. Conversely, the human progesterone receptor (hPR) clearly shows cooperative binding to paired responsive elements (PREs) under similar conditions in vitro. Thus, hER molecules bound to adjacent EREs must be properly stereoaligned to activate transcription synergistically in vivo. However, our data suggest that this synergism is not primarily due to cooperative binding to the EREs.

Adenoviruses, Human↗
PubMed1990

Expression of the yeast DNA primase gene, PRI1, is regulated within the mitotic cell cycle and in meiosis.

Mitotic cultures synchronised either by a feed-starve protocol or by elutriation have been used to show that the Saccharomyces cerevisiae DNA primase I gene is periodically expressed in the cell cycle. The transcript increases many-fold in late G1 and reaches a peak at the same time as four other genes essential for DNA synthesis, CDC8, CDC9, CDC21 and POL1. The primase I transcript is also regulated in meiosis, reaching maximal levels during premeiotic DNA synthesis.

DNA Primase↗
PubMed1989

Dependence of the linking deficiency of supercoiled minichromosomes upon nucleosome distortion.

The contribution from each nucleosome to the linking number of minichrosome DNA depends on two factors. These are the wrapping number, omega, which is the number of times the DNA wraps about the axis of the nucleosome; and the winding number, phi, which is the number of base pairs on the nucleosome divided by the helical repeat of the DNA. If the nucleosome is distorted with DNA surface contacts being preserved, phi remains unchanged. The wrapping number may still change, however, depending on the extent of the distortion. For example, if the usual cylindrical shape of the nucleosome is deformed into an ellipsoid while preserving the equatorial radius, then the wrapping number will increase. We apply these concepts to minichromosomes torsionally stressed by supercoiling with, for example, DNA gyrase. We analyze the experimental result that the maximum amount of supercoiling obtained by gyrase treatment of minichromosomes is the same as that of naked DNA. In particular, we show that this phenomenon can be explained by a relatively slight distortion of the nucleosome core while maintaining the surface contacts of the DNA on the core.

Chromosomes↗
PubMed1989

Effect of nucleosome distortion on the linking deficiency in relaxed minichromosomes.

The wrapping of closed circular DNA on a protein surface, followed by relaxation with a topoisomerase and removal of proteins, produces a characteristic DNA linking deficiency, delta Lk. We show that the magnitude of delta Lk depends upon the surface shape, and we calculate changes in delta Lk caused by particular distortions of the protein wrapping surface. If the DNA remains attached to the surface during distortion, the DNA winding number, phi, is not altered. The change in delta Lk is then equal to the change in the surface linking number, SLk, which is a straightforward measure of the wrapping of the DNA around the surface. For left-handed wrapping, as in a nucleosome, SLk = -n, the number of times that the DNA axis winds around the axis of the protein complex. We calculate values of SLk for the helical wrapping of a constant length of DNA on protein surfaces having the shapes of cylinders and of ellipsoids and hyperboloids of revolution. If the equatorial radius of the protein is fixed, change in shape from a cylinder to a hyperboloid increases SLk, while the corresponding change to an ellipsoid reduces SLk. We apply the general results to the interpretation of experiments in which minichromosomes are relaxed with topoisomerase at various temperatures and delta Lk is determined. The result is that a distortion of the nucleosome core by at most 5% (the change in the radius at the axial extremity relative to the equator) is sufficient to explain the observed delta Lk changes.

Animals↗
PubMed1989

Preliminary observations of a bacteriophage infecting Xenorhabdus luminescens (Enterobacteriaceae).

A bacteriophage infective to Xenorhabdus luminescens, a bacterial symbiont of heterorhabditid nematodes, was recovered from insects that supported poor nematode development. Plaque tests showed the phage particles to be infective only to primary and not secondary colonies of X. luminescens. The phage was not infective to X. nematophilus primaries or secondaries. The bacteriophage particles ranged 80-90 nm in length, with the head ranging from 40 to 50 nm in diameter. Restriction analysis was performed on isolated bacteriophage DNA. This first report of a bacteriophage from Xenorhabdus species has practical implications since it could be detrimental to cultures of Heterorhabditis nematodes that are being produced throughout the world for the biological control of insects.

Animals↗
PubMed1979

Davidoff-Dyke-Masson syndrome presenting as childhood schizophrenia.

The problem of differential diagnosis of childhood schizophrenia versus gross brain pathology is a difficult one. The clinical picture, for instance, of dementia infantalis (Heller's Disease) is indistinguishable from that of schizophrenia (Shaw & Lucas, 1970). The same is true of some major metabolic disorders (Bray,1970). Coexisting neurological and EEG findings for seizures are not helpful since these are often seen in schizophrenia (Bender, 1947; Fish, 1977). Mental retardation may coexist with schizophrenia or any of the other disorders. The following is an unusual case illustration of a child presenting symptoms of schizophrenia, seizures, and retardation without neurological abnormalities. Until his gross anatomical brain pathology was found by neurologic evaluation, he was subjected to the inappropriate treatment of psychotherapy.

Atrophy↗
PubMed1979

Pedicle skin flap to prevent corneal perforation.

A pedicle skin flap from the lower eyelid was passed through the lower eyelid into the lower fornix and sutured over the cornea in a 36-year-old man with impending perforation caused by lye burns. Perforation was avoided but occurred in the control eye.

Adult↗
PubMed1979

A maternal death associated with prostaglandin E2.

A maternal death following prostaglandin E2 (PGE2) administration is reported. It is suggested that prostaglandin may not be safer than other methods of uterine evacuation for late abortion and fetal death.

Abortion, Therapeutic↗