bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toxicity, Mutagenesis and Stress Responses Induced in Escherichia Coli by Hydrogen Peroxide
Authors: Linn Stuart , Imlay James A. 
Published: May 2013

ABSTRACT
Two modes of killing of Escherichia coli by hydrogen peroxide can be distinguished. Mode-one killing is maximal at 1–2MM; at higher concentrations the killing rate is approximately half- maximal and is independent of H2O2 concentration but first order with respect to exposure time. Mutagenesis and induction of a phage lambda lysogen are similarly affected by H2O2 concentration, with reduced levels of response above 1–2 mM-H2O2. Mutagenesis is not affected by inactivation of umuC. Mode-one killing requires active metabolism during the H2O2 challenge and it results in sfiM-independent filamentation of both cells that survive and those that are killed by the challenge. This mode of killing is enhanced in xth, polA, recA and recB strains; however, it is unaffected by mutations in the nth, uvrA, uvrB, uvrC, uvrD, rep, gyrA, htpR and rel loci. Mode- one killing is normal in strains totally lacking catalase activity (katE, katG), glutathione reductase (gor) or glutathione synthetase (gshB), but enhanced in a strain lacking NADH dehydrogenase (ndh). Mode-one killing is accelerated by the presence of CN− or by an unidentified function that is induced by anoxic growth and is under the control of the fnr locus. A strain carrying both xth and recA mutations and certain polA mutants appear to undergo spontaneous mode-one killing only under aerobic conditions. Taken together, these observations imply that mode-one killing results from DNA damage that normally occurs at a low, non-lethal level during aerobic growth. Models for the resistance to mode-one killing at doses above l–2mM-H2O2 will be discussed.
Mode-two killing occurs at high concentrations of H2O2 and longer times. It does not require active metabolism, and cells that are killed do not filament, although survivors demonstrate a dosedependent growth lag followed by a period of filamentation. Mode-two killing is accompanied by enhanced mutagenesis, but strains with DNA repair defects were not observed to be especially sensitive to this mode of killing.
Strategies to Analyse Mutagenesis in Mammalian Cells Using Simian Virus 40 or Shuttle Vectors
Authors: Menck Carlos F. M. , James Michael R. , Gentil Alain , Sarasin Alain 
Published: May 2013

ABSTRACT
The use of exogeneous DNA probes, which replicate extrachromosomally, is proposed in order to study spontaneous and induced mutagenesis in mammalian cells. Simian virus 40 has already proved to be very useful, since it has provided much important information in this field. Recently, several shuttle vectors have been designed for this purpose; however, it seems that these molecules have high spontaneous mutation frequencies when replicating in mammalian cells. We have developed new alternative systems, such as Epstein-Barr virus-based shuttle vectors that can be episomally maintained in human cells. Furthermore, we have constructed packageable shuttle vectors, which appear to be stable in the host cell and thus suitable for analysis of mutagenesis.
A Gamma-Ray-Resistant Derivative of an Ataxia Telangiectasia Cell Line Obtained Following DNA-Mediated Gene Transfer
Authors: Green Michael H. L. , Lowe Jill E. , Arlett Colin F. , Harcourt Susan A. , Burke Julian F. , James Michael R. , Lehmann Alan R. , Povey Susan M. 
Published: May 2013

ABSTRACT
Genomic DNA from normal human or mouse cells was transfected together with the selectable marker gpt into the simian virus 40-transformed ataxia telangiectasia fibroblast line, AT5BIVA. From a series of experiments involving over 400000 clones selected for the gpt marker, one unambiguously radiation-resistant clone (clone 67) was recovered following selection with repeated cycles of gamma irradiation.
The normal level of radiation resistance of clone 67 has been maintained for at least 11 months in the absence of further selection by radiation. The resistant clone contains one copy of the gpt gene. Its DNA synthesis following gamma-irradiation is inhibited to an extent intermediate between that of ataxia telangiectasia and normal cells.
Three out of four thioguanine-resistant derivatives of clone 67 have either lost or do not express the gpt sequence and show almost the same sensitivity to gamma irradiation as the original AT5BIVA line. This suggests that the radiation resistance of clone 67 may be linked to the gpt sequence and may have arisen as a consequence of the transfection, rather than as the result of an independent mutation to radiation resistance.
Properties and Mechanism of Action of Eukaryotic 3-Methyladenine-DNA Glycosylases
Authors: Helland D. E. , Male R. , Haukanes B. I. , Olsen L. , Haugan I. , Kleppe K. 
Published: May 2013

ABSTRACT
3-Methyladenine-DNA glycosylase activities have been identified in all eukaryotic cell systems studied. Some of the results from these studies are reviewed here. The enzymes possess molecular weights between 24 ×101 and 34 ×101, they have a broad pH optimum at approximately pH 8, require double-stranded DNA and act in the absence of any cofactors. The enzyme can excise several different methylated bases from DNA such as 3-methyladenine, 7-methylguanine and 3-methylguanine.
The specific activity of this DNA glycosylase in mouse L-cells was found to be a function of the proliferative state of the cell. In vitro quantification of this DNA repair activity in synchronized mouse L-cells suggests that it is regulated within a defined temporal sequence prior to the onset of DNA replication.
Using DNA fragments of defined sequences it was observed that the efficiency of removal of the methylated bases is sequence-dependent.
The legvme-rhizobium symbiosis: a cell surface interaction
Authors: Robertson J. G. , Wells B. , Brewin N. J. , Wood E. , Knight C. D. , Downie J. A. 
Published: May 2013

ABSTRACT
This review will examine the early stages of infection of legume roots by strains of Rhizobium that induce nitrogen-fixing nodules. The object is to show that, at least in terms of ultrastructure, the interactions between the plant and the rhizobia occur at the cell surface interface between these organisms. This situation exists at all stages, from the time the bacteria attach to the surface of the root hairs to the time they occur as the nitrogen-fixing form in the cytoplasm of the nodule cells, enclosed by peribacteroid membranes.
The cytoskeleton underlying side walls and cross walls in plants: molecules and macromolecular assemblies
Authors: Lloyd C. W. , Clayton L. , Dawson P. J. , Doonan J. H. , Hulme J. S. , Roberts I. N. , Wells B. 
Published: May 2013

ABSTRACT
Plant cells organize their growth by reinforcing side walls during interphase (causing them to elongate) and by positioning and orienting the cross wall at cytokinesis. In the first part of this presentation we review progress made in identifying different cytoskeletal components that underlie side walls and that are involved in the deposition of the cross wall.
During interphase, the cortical microtubule arrays co-distribute with an antigen recognized by a ‘universal’ monoclonal antibody to intermediate filaments.
Using rhodaminyl-lysine-phalloidin no F-actin could be detected at the cortex but endoplasmic, axial cables were found. The cytokinetic apparatus -the phragmoplast -contains microtubules and we find that F-actin and the intermediate filament antigen also co-distribute with this array.
We describe the three-dimensional arrangement of microtubules forming the interphase array in cells enlarging by both tip-growth and intercalary growth. In root hairs of higher plants and in apical cells of the filamentous stage of moss Physcomitrella patens, microtubules (MT) are detected at the apices and it is suggested from this that fragmentation of microtubules and absence of MTs from the tip are preparation artefacts.
Using human serum from a scleroderma patient, possible microtubule nucleating sites are detected in meristematic cells; these segregate with the broad spindle poles and they surround the nucleus during early interphase -implying a peri-nuclear origin for the cortical MT array.
The interphase microtubule array is described in terms of a dynamic helical model, which proposes : that the MT array is an integral complex; that microtubules form helices ; that helices can change their pitch -the array converting to the various conformations.
The use of anti-synthetic peptide antibodies to study the v-erb b protein from chicken and rat cells transformed by avian erythroblastosis virus
Authors: Gullick W. J. , Marsden J. J. , Downward J. , Waterfield M. D. 
Published: May 2013

ABSTRACT
Two site-specific anti-peptide antisera have been produced that efficiently recognize the native form of the v-erb B protein from avian erythroblastosis virus(AEV)-infected chicken erythroblasts and fibroblasts, and from AEV-transformed mammalian cells. Since the antibodies were generated against synthetic sequences, the immunoprecipitations could be performed in the presence or absence of immunizing peptide, permitting the specifically precipitated proteins to be identified from background non-specifically adsorbed proteins. We confirmed that immobilized v-erb B protein from cell lysates of unlabelled AEV-infected chicken erythroblasts became labelled upon incubation with [γ−32P]ATP. In addition we demonstrated for the first time that v-erb B from mammalian cells became labelled under the same conditions. These results suggest that the v-erb B protein may possess intrinsic kinase activity. The reagents described should permit further investigations as to whether this activity plays a role in maintaining cellular transformation.
Phosphoinositides and cell proliferation
Authors: Berridge Michael J. , Brown Kenneth D. , Irvine Robin F. , Heslop John P. 
Published: May 2013

ABSTRACT
Certain growth factors act by stimulating the hydrolysis of inositol lipids to yield putative second messengers such as diacylglycerol (DG) and inositol trisphosphate (IP3). One function of the former is to stimulate C-kinase, which may act by switching on a sodium/hydrogen exchanger to induce the increase in pH that appears to have a permissive effect on DNA synthesis. Studies on Swiss 3T3 cells have revealed that growth factors stimulate an increase in two separate isomers of IP3. In addition to inositol 1,4,5-trisphosphate there was a large increase in inositol 1,3,4-trisphosphate. While the former functions to elevate intracellular calcium, which has been implicated in the control of growth of many different cell types, the function of the latter is unknown. Since the 1,3,4 isomer turns over very slowly, it may control long-term events and thus could play a role in cell growth.
There are other growth factors such as insulin and epidermal growth factor (EGF), which apparently do not work through the inositol lipids but they may initiate ionic events similar to those just described for calcium-mobilizing receptors. The bifurcating signal pathway based on IP3/Ca2+ and DG/C-kinase provides an interesting framework within which to consider the mode of action of oncogenes.
Vesicle Movements And Microtubule-Based Motors
Authors: P. Sheetz Michael , Vale Ronald , Schnapp Bruce , Schroer Trina , Reese Thomas 
Published: May 2013

ABSTRACT
The movements of many cytoplasmic vesicles follow the paths of microtubules, some moving in one direction and others moving in the opposite direction on the same microtubule. Recently we have isolated one cytoplasmic motor, kinesin, and defined another, the axoplasmic retrograde factor, both of which are capable of powering anionic latex beads in both directions along polar microtubule arrays. Evidence summarized here supports but does not prove the hypothesis that kinesin and the retrograde motors are indeed responsible for powering vesicle movements.
Characterization Of The Sea-Urchin Egg Microtubule-Activated Atpase
Authors: A. Collins Christine , B. Vallee Richard 
Published: May 2013

ABSTRACT
We have found that cytoplasmic extracts from unfertilized sea-urchin eggs contain a prominent microtubule-activated ATPase activity. This activity is induced by polymeric tubulin, but not by tubulin subunits. The activity cosediments with taxol-stabilized microtubules in an ATP- independent manner. We have separated the ATPase from cytoplasmic dynein and other ATPases on sucrose gradients. The sedimentation, enzymic and microtubule-binding properties of the microtubule-activated species show it to be distinct from cytoplasmic dynein, myosin and kinesin. Since the major function of microtubules in the early sea-urchin embryo is in mitosis, this enzyme represents a new candidate for a role in spindle motility.
The Role Of Microtubule Polarity In The Movement Of Kinesin And Kinetochores
Authors: J. Mitchison T. 
Published: May 2013

ABSTRACT
Microtubules are important for organizing and directing many types of intracellular motility. Recently progress has been made in the analysis of two types of motility at the molecular level: the movement of axonal vesicles driven by kinesin, and the movement of chromosomes driven by the kinetochore. Both require ATP for movement in vitro. Kinesin-driven movement is unidirectional, towards the microtubule plus end, while movement of the kinetochore is bidirectional. These similarities and differences are discussed and incorporated into a new model for the kinetochore- microtubule interface.
Reticulomyxa: A New Model System Of Intracellular Transport
Authors: Koonce Michael P. , Euteneuer Ursula , Schliwa Manfred 
Published: May 2013

ABSTRACT
Reticulomyxa is a large multinucleated freshwater protozoan that provides a new model system in which to study intracellular transport and cytoskeletal dynamics. Within the cell body and reticulopodial network, rapid, visually striking saltatory organelle motility as well as bulk cytoplasmic streaming can be readily observed. In addition, the cytoskeletal elements within these strands undergo dynamic splaying and fusing rearrangements, which can be visualized by videoenhanced light microscopy. A reactivatable lysed cell model has been developed that appears to preserve, and therefore permits examination of, these three forms of motility in a more controlled environment. Individual organelle movements are microtubule-based and have similarities to, but also differences from, the recently described kinesin-based transport. This lysed cell model can be further manipulated to provide native, ordered, completely exposed networks of either microtubules or microfilaments, or a combination of both, and thus may serve as a versatile motility assay system in which to examine the movement of exogenously added isolated organelles or latex beads.
Retrovirus genome replication: priming specificities of plus-strand dna synthesis
Authors: Taylor John , Sharmeen Lamia 
Published: May 2013

ABSTRACT
The retroviral reverse transcriptase is a multifunctional protein. Not only does it contain both RNA- and DNA-directed DNA synthesis activities but also it contains an endonuclease activity necessary for the integration of viral RNA and a RNase H. This latter activity can reduce to oligoribonucleotides viral RNA that has been reverse transcribed into minus-strand DNA. However, during avian retrovirus genome replication it does this in a highly specific manner so as to generate a specific 12-base primer for plus-strand DNA synthesis. Even though many other oligoribonucleotides are also made there is an efficient selection xof the specific primer followed by its efficient utilization in plus-strand DNA synthesis, and subsequent removal. We have used a reconstructed system to gain an understanding of the factors that contribute towards these observed specificities.
Dna and protein interactions in the regulation of plasmid replication
Authors: Filutowicz Marcin , Mceachern Michael J. , Mukhopadhyay Pradip , Greener Alan , Yang Shengli , Helinski Donald R. 
Published: May 2013

ABSTRACT
As for bacterial and animal viruses that employ different mechanisms for their duplication in a host cell, plasmids have evolved different strategies to assure their hereditary stability or maintenance at a specific copy number during cell growth and division. A characteristic feature of plasmid replication control, however, is an involvement of one or more negatively controlling elements. Furthermore, a majority of the bacterial plasmids examined to date contain direct nucleotide sequence repeats at their origin of replication and encode a replication protein that binds to these repeat sequences. The binding of the replication protein (n protein) specified by the antibiotic resistance plasmid R6K to a set of 22 base pair direct nucleotide sequence repeats is required for the initiation of replication at each of three origins of replication (α, βand γ) within a 4 Kb segment of R6K. The π initiation protein is multifunctional in that it has both positive and negative activities in both controlling the initiation of replication and autoregulating its own synthesis. Similarly, the direct repeats of plasmid R6K and several other plasmid systems play more than one role in plasmid replication. These repeats, termed iterons, are not only required for origin activity but also exert a negative effect on plasmid copy number possibly as a result of their ‘titration’ of a plasmid encoded replication protein. The properties of plasmid replication proteins and direct nucleotide sequence repeats that are important for their opposing positive and negative roles in the regulation of the initiation of replication are described with particular emphasis on plasmid R6K of Escherichia coli.
Actin Cortex and Microtubular System in Morphogenesis: Cooperation and Competition
Authors: Vasiliev J. M. 
Published: May 2013

ABSTRACT
Actin cortex and microtubules determine two different types of morphological organization of the cytoplasm. Cooperation and competition between these two organizations may produce a diversity of final forms. Actin cortex alone, without the other cytoskeletal systems, is sufficient for the organization of vectorized pseudopod-forming cytoplasmatic units termed ‘actinoplasts’. Reversible segregation of cytoplasm into actinoplasts and microtubule-rich stable domains (‘tubuloplasts’) is suggested to play an important role in many types of morphogenesis. Segregation of this type can be induced in fibroblasts of certain lines by the tumour promotor, tetradecanovl phorbol-acetate (TPA). Self-organization of each actinoplast leads to the development of microfilament bundles associated with focal contacts. Analysis of the evolution of these bundle-contact structures during spreading of mouse fibroblasts suggests that their patterns are determined by the degree of centripetal tension within the actin cortex; the microtubular system stabilizes these patterns. Pseudopodia! activity of the edges of the actinoplasts can be controlled by environmental factors. One particular type of control, i.e. the effect of cell-cell contact, is discussed. Actin cortex and microtubules seem to have alternative effects on the distribution of vimentin-containing intermediate filaments.
Adhesion Plaques: Sites of Transmembrane Interaction Between the Extracellular Matrix and the Actin Cytoskeleton
Authors: Burridge Keith , Molony Leslie , Kelly Thomas 
Published: May 2013

ABSTRACT
In this paper we review what is known about the organization of adhesion plaques, the regions where cells in culture adhere most tightly to the underlying substratum. These specialized areas of the plasma membrane serve as attachment sites for stress fibres. A major objective has been to determine how microfilament bundles are anchored at such regions. In their morphology and composition adhesion plaques resemble the adhesions fibroblasts make to the extracellular matrix. Some extracellular matrix components have been identified on the outside face of adhesion plaques. Within the plasma membrane of adhesion plaques, extracellular matrix receptors, such as the fibronectin receptor (integrin), have been identified. This transmembrane glycoprotein complex has been shown to bind the cytoplasmic protein talin, which, in turn, associates with vinculin. These proteins establish a transmembrane chain of attachment between the extracellular matrix and the cytoskeleton, although how the actin filaments interact with these components remains to be determined. Besides having a structural function, adhesion plaques may also be regions where regulatory signals are transmitted across the membrane. Consistent with this idea has been the finding that various tyrosine kinases and a calcium-dependent protease are concentrated at the cytoplasmic aspect of adhesion plaques. Furthermore, several adhesion plaque proteins become phosphorylated during cell transformation by Rous sarcoma virus. In future work it will be important to determine how such modifications affect the interactions of these proteins and the stability of adhesion plaques.
Molecular Interactions in Adherens-Type Contacts
Authors: Geiger Benjamin , Volk Talila , Volberg Tova , Bendori Ronit 
Published: May 2013

ABSTRACT
Adherens junctions are members of a molecularly and structurally heterogeneous family of cell contacts sharing a common association with the microfilament system. Various topics related to the biogenesis of these cellular contacts and the molecular interactions involved in their formation are discussed. ⅓ The role of vinculin, a cytoplasmic ‘plaque’ component present in all adherens junctions tested to date and its possible interactions with the other junctional domains have been investigated by both biochemical analyses and studies of molecular dynamics in microinjected living cells. The importance of A-CAM, which apparently functions as a ‘junctional receptor’ is emphasized and its roles in junction formation in cell cultures and in developing embryos are discussed. In addition, its relationship to other Caz+-dependent cell adhesion molecules (in particular L-CAM) is considered. The evidence indicating that the level of expression of vinculin-specific mRNA is affected by culture conditions and may be markedly modulated by changes in the adhesiveness of the substratum on which the cells grow is reviewed.