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L S Cox

Publications and source records attributed to L S Cox.

27 records · Page 2Linked to original sources
PubMed1992

DNA replication in cell-free extracts from Xenopus eggs is prevented by disrupting nuclear envelope function.

The lectin, wheat germ agglutinin (WGA), has previously been shown to prevent transport into the cell nucleus. This paper shows that WGA also inhibits nuclear DNA replication, under the same conditions that prevent transport. Although WGA eliminates sperm nuclear DNA replication in a cell-free extract of Xenopus eggs, DNA synthesis on a single-stranded template proceeds normally. Inhibition of nuclear DNA replication is partially reversed by addition of N-acetylglucosamine, and completely reversed by triacetylchitotriose. Sensitivity to inhibition by WGA is greatest during the nuclear assembly phase, and nuclear formation on sperm chromatin is blocked. DNA replication in preformed nuclear templates is also sensitive to WGA inhibition. I propose that WGA blocks DNA replication by preventing nuclear transport. The data presented here also indicate that, under certain circumstances, the elongation stage of DNA replication does not proceed in the absence of an intact nuclear envelope. The roles of the nuclear envelope and active nuclear transport in DNA replication are discussed.

Acetylglucosamine↗
PubMed1991

DNA replication occurs at discrete sites in pseudonuclei assembled from purified DNA in vitro.

Bacteriophage lambda DNA is assembled into pseudonuclei in Xenopus egg extract and replicated semiconservatively under temporal cell cycle control. Here, replication is shown to be regulated spatially and to occur at discrete sites that represent clustered replication forks. Clustered forks are visualized by incorporation of biotin-19-dUTP into nascent DNA. Pulse-label experiments show that discrete replication foci persist throughout S phase. We conclude that the organization of replication forks into discrete clusters, previously described in eukaryotic nuclei, is not dependent on specific eukaryotic DNA sequences or on a preexisting inherited chromosomal or nuclear structure.

Animals↗
PubMed1990

Extracts from eggs and oocytes of Xenopus laevis differ in their capacities for nuclear assembly and DNA replication.

We describe a cell-free extract derived from the oocytes of Xenopus laevis. The oocyte extract is capable of decondensing sperm chromatin and of replicating single-stranded DNA in a semiconservative, aphidicolin-sensitive manner. In addition, oocyte extract supports the elongation phase of DNA synthesis in nuclei that have been preinitiated for replication. All of these properties are shared by previously described egg extracts. However, oocyte extracts differ from egg extracts in two important ways. First, they cannot support nuclear assembly, as visualised by phase-contrast, fluorescence and electron microscopy. Second, they do not initiate replication on chromatin or nuclei de novo. Crude low-speed supernatants can be partially fractionated into soluble and vesicular components by high-speed centrifugation. Such fractions from eggs can be functionally reconstituted, but the oocyte soluble fraction does not acquire the ability to assemble nuclei, or replicate them, even when supplemented with the egg vesicular fraction. Similarly, oocyte vesicles cannot substitute for egg vesicles on reconstitution with the egg soluble fraction. When the requirement for nuclear assembly is bypassed by using preformed, quiescent nuclei, replication is observed in egg but not oocyte extracts. However, the oocyte extract is not inhibitory for initiation of replication, as it does not prevent replication of sperm nuclei when mixed with egg extract. We suggest that the different capabilities of egg and oocyte extracts could provide the basis of an assay system for identifying factors involved in the initiation of DNA replication.

Animals↗
PubMed1987

Nucleoplasmin cDNA sequence reveals polyglutamic acid tracts and a cluster of sequences homologous to putative nuclear localization signals.

Nucleoplasmin is the most abundant protein in the Xenopus oocyte nucleus. It is involved in histone storage and chromatin assembly and it has been used extensively to study the transport of proteins into the cell nucleus. We have isolated lambda gt11 phage containing nucleoplasmin cDNA and have determined the sequence of the entire protein coding region of 200 amino acids for one of the two genes. The translation product of the sp6 transcript of this cDNA has the same electrophoretic mobility as nucleoplasmin and is able to form pentamers. The protein sequence shows remarkable clusters of charged residues including a long polyglutamic acid tract which presumably constitutes the histone binding site. The short C-terminal domain which specifies nuclear entry contains four regions which are homologous to putative nuclear localization signals including two regions of homology to the nuclear migration signal of SV40 large T antigen.

Amino Acid Sequence↗
PubMed1982

The dexamethasone suppression test in mania.

The results of the overnight 2 mg Dexamethasone Suppression Test administered to 50 manic patients are reported. Twenty-three (46%) cases showed an absence of normal suppression, results which are similar to those seen in endogenous depression and which differ to those of others who have all reported normal suppression in mania. Suppressors and non-suppressors were not shown to differ in the factors of age, weight, polarity or the rated severity of mood.

Adult↗
PubMedDate not supplied

Associative and nonassociative tolerance: the effects of dose and interdose interval.

Two experiments examined the effects of dose and interdose interval (IDI) on associative and nonassociative tolerance to morphine analgesia in rats. Associative contingencies were manipulated by administering low (5 mg/kg) or high (20 mg/kg) doses of morphine explicitly paired or unpaired with a distinctive context. Nonassociative processes were manipulated by administering morphine at a short (6-h) or long (96-h) IDI. Tolerance was assessed as shifts in morphine dose-response curves on the tail-flick test. Animals in the long IDI conditions showed considerable context-specific tolerance. Tolerance in the short IDI conditions was not influenced by contextual contingencies at the immediate test (Experiment 1) and showed no retention over a 30-day interval (Experiment 2), suggesting this tolerance was nonassociative. The impact of massed exposure to morphine and context on the disruption of learning at the short IDI is discussed.

Analgesics, Opioid↗
PubMedDate not supplied

MDM2 and MDMX bind and stabilize the p53-related protein p73.

The p53 gene encodes one of the most important tumor suppressors in human cells and undergoes frequent mutational inactivation in cancers. MDM2, a transcriptional target of p53, binds p53 and can both inhibit p53-mediated transcription [1] [2] and target p53 for proteasome-mediated proteolysis [3] [4]. A close relative of p53, p73, has recently been identified [5] [6]. Here, we report that, like p53, p73alpha and the alternative transcription product p73beta also bind MDM2. Interaction between MDM2 and p53 represents a key step in the regulation of p53, as MDM2 promotes the degradation of p53. In striking contrast to p53, the half-life of p73 was found to be increased by binding to MDM2. Like MDM2, the MDM2-related protein MDMX also bound p73 and stabilized the level of p73. Moreover, the growth suppression functions of p73 and the induction of endogenous p21, a major mediator of the p53-dependent growth arrest pathway, were enhanced in the presence of MDM2. These differences between the regulation of p53 and p73 by MDM2/MDMX may highlight a physiological difference in their action.

Cell Division↗
PubMedDate not supplied

Hastening death: a comparison of two end-of-life decisions.

This study determined the relationship of psychosocial and background variables to elders' end-of-life (EOL) decision preferences. Responding to 5 EOL decision scenarios depicting terminally ill elders, 200 elders aged 60-90 indicated preferences regarding extending life (EL), refusing treatment (RT), and assisted suicide (AS). They were also assessed on religiosity, values, fear of death, locus of control, health, socioeconomic status, and age. Results of multinomial logistic regression indicated that EOL decisions of three groups (favoring EL, favoring RT, and favoring both AS and RT) were significantly influenced by religiosity, value for preservation of life, value for quality of life, fear of death, and locus of control belief. The importance of safeguarding older adults' autonomy in EOL decisions was stressed.

Aged↗