bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular events associated with the action of haemopoietic growth factors
Authors: Farrar William L. , Evans Stuart W. , Harel-Bellan Annick , Ferris Douglas K. 
Published: May 2013

ABSTRACT
Haemopoietic growth factors stimulate a number of consensus biochemical and molecular events regardless of the specificity detailed by unique ligand and receptor structures. Analysis of three distinct colony stimulating factors, CSFs (IL-3, G-CSF, GM-CSF) and the lymphocytotropic growth factor IL-2 reveal remarkable similar distal subcellular biochemical signals although initial membrane ‘signal transduction’ may differ significantly. Both early progenitor cell growth factors, such as IL-3, and late acting factors such as CSF-1, stimulate tyrosine and serine-threonine substrate phosphorylations. One substrate (p68) is phosphorylated by many CSF stimulants, including IL-2, suggesting a highly conserved role in many unique receptor(s) signal transduction processes. The proliferative CSFs and IL-2 also stimulate the expression of many of the same genes including proto-oncogenes, ornithine decarboxylase and members of the ancient family of stress response genes. Although initial membrane events may differ among the respective proliferative stimulants, biochemical and molecular convergence on highly conserved cellular substrates and the programme of gene expression is seen.
Interaction between mitochondria and the nucleus
Authors: Pon Liza A. , Vestweber Dietmar , Yang Meijia , Schatz Gottfried 
Published: May 2013

ABSTRACT
The interaction between the mitochondrial and the nuclear genome is in part mediated by proteins (and possibly also RNAs) which are encoded in the nucleus and imported into mitochondria. We are beginning to understand how proteins can penetrate across both mitochondrial membranes and how some of these proteins can regulate the expression of specific mitochondrial genes.
Biochemical investigation of protein export in Escherichia coli
Authors: Hardy S. J. S. , Randall L. L. 
Published: May 2013

ABSTRACT
Export of proteins from the bacterial cytoplasm to a final destination in the periplasm and outer membrane is one example of the fundamental process occurring in all cells whereby polypeptides are transferred across biological membranes. Investigations on a variety of different systems have indicated similarities in the mechanism of this process. In the cases of bacterial protein export and the transfer of polypeptides across the endoplasmic reticulum in eukaryotic cells the processes are so similar that understanding gleaned from studies of the one is usually directly applicable to the other.
The study of protein export in E. coli has two advantages over that of eukaryotic secretion. Not only is there the possibility of doing sophisticated genetic experiments, but also one can carry out biochemical investigations in vivo, a facility not so readily available with eukaryotic organisms. Such studies have, for example, shown that membrane translocation can occur both co- translationally and post-translationally, that export requires protonmotive force, that some component of the export apparatus prevents the exported protein from assuming its native structure in the cytosol, and that there are probably at least two functions for the leader sequence, one in targeting the protein to the export pathway and one in translocation across the membrane.
Genetic and biochemical analysis of protein export from Xanthomonas campestris
Authors: Dow J. M. , Daniels M. J. , Dums F. , Turner P. C. , Gough C. 
Published: May 2013

ABSTRACT
Xanthomonas campestris pv. campestris, a Gram-negative phytopathogen, produces a number of extracellular enzymes which can degrade components of the host plant cell. Some non-pathogenic mutants, derived by chemical mutagenesis, were found to be defective in the export but not the synthesis of a number of these enzymes. The pathogenicity and export lesions in one such mutant, strain 8288, could be complemented by a cosmid clone pIJ3000 from the Xanthomonas library. Mutagenesis of pIJ3000 with the transposon Tn5 followed by recombination into the corresponding region of the chromosome has revealed a cluster of 6 to 8 genes whose function is required for enzyme export. Sequence analysis of part of the cluster has revealed two open reading frames that would encode proteins with extensive hydrophobic domains. Export-defective mutants retain the normally exported enzymes in the periplasmic space. These forms have the same molecular weight as the extracellular forms, suggesting that the signal sequence has been properly processed. The results are consistent with a mechanism of sequential translocation across cytoplasmic and outer membrane via the periplasm. The second translocation step may be mediated by the products of the export genes. This may be a common export mechanism amongst Gram-negative bacteria but other mechanisms do exist, sometimes in parallel in the same cell, and these are briefly reviewed.
Calcium-induced chromatin condensation and cyclin phosphorylation during chromatin condensation cycles in ammonia-activated sea urchin eggs
Authors: Patel Rajnikant , Twigg Jeremy , Crossley Ian , Golsteyn Roy , Whitaker Michael 
Published: May 2013

ABSTRACT
Ammonia-activated sea urchin eggs undergo repeated cycles of DNA synthesis, nuclear envelope breakdown (NEB) and chromatin condensation. No mitotic spindle forms, nor do the eggs undergo cytokinesis. Ammonia-activated eggs exhibit a form of the cell cycle in which the nuclear cycle proceeds without segregation of the chromatin into daughter cells. We discuss here experiments that demonstrate that intracellular free calcium concentration controls the S phase-M phase transition in ammonia-activated eggs, as it does in fertilized embryos.
Cyclins are proteins that are synthesized throughout the cell cycle and destroyed abruptly during each round of chromatin condensation. We find that cycles of cyclin phosphorylation and destruction occur coincident with chromatin condensation in ammonia-activated eggs. Cyclin phosphorylation also occurs in eggs treated with the tumour promoter, phorbol myristate acetate (PMA). There is no accompanying NEB or chromatin condensation, however, and the nucleus is insensitive to exogenously-generated calcium transients. These latter data indicate that cyclin synthesis and phosphorylation is not a sufficient condition for calcium-induced NEB in sea urchin embryos. PMA must fail to induce one of the necessary cell cycle initiation signals. We suggest that the missing signal is the activation of the cell cycle control protein p34cdc2, which we have shown to be phosphorylated at fertilization and which is phosphorylated in ammonia-activated eggs.
Replication of SV40 in vitro using proteins derived from a human cell extract
Authors: Fairman M. P. , Prelich G. , Tsurimoto T. , Stillman B. 
Published: May 2013

ABSTRACT
In the presence of large T antigen and plasmids containing a functional origin of replication, extracts from a human cell line will support multiple rounds of simian virus 40 (SV40) replication in vitro. Fractionation of this extract has led to the identification of several factors, some of which have been purified to homogeneity. The characterisation of these proteins has led to the separation of SV40 replication in vitro into multiple stages.
Two proteins, the cell cycle-regulated proliferating cell nuclear antigen and replication factor-C, have been shown to be essential for coordinating leading and lagging strand synthesis in this system. Another protein, replication factor-A, is a multi-subunit protein of 70, 34 and 11K (K = 103Mr) polypeptides which, because of its high affinity for DNA, is thought to function as a eukaryotic single-stranded DNA binding protein. Interactions between other cellular factors are also described that effect the initiation of DNA replication, but are not required in a more purified system. In addition a model for a hypothetical replication fork is described, which suggests a role for both a- and ô-polymerases in this system, and may be applicable to higher eukaryotes.
Nuclear structure and the control of DNA replication in the Xenopus embryo
Authors: Blow J. J. , Sheehan M. A. , Watson J. V. , Laskey R. A. 
Published: May 2013

ABSTRACT
We have developed a cell-free system from frog eggs that efficiently initiates and completes a single round of semi-conservative replication. 70–100% of sperm chromatin and up to 40% of plasmid DNA molecules are completely replicated in vitro. Before DNA is replicated it is assembled into nuclei surrounded by a double unit membrane studded with nuclear pores. Flow cytometry shows that initiation events are co-ordinated within individual nuclei, although different nuclei can start to replicate at different times in the same extract. This demonstrates the importance of nuclear structure in the control of DNA replication in this system.
Only a single round of semi-conservative replication occurs in the cell-free system. This mirrors the way that only one round of DNA replication occurs in each cell cycle in vivo. When replicated nuclei are transferred to fresh extract they are unable to undergo another round of replication. However, if the nuclear envelope is permeabilised before nuclei are transferred to fresh extract, the DNA becomes capable of undergoing a further round of semi-conservative replication. These results suggest a simple model for the control of DNA replication within the cell cycle, whereby an essential initiation factor can only gain access to DNA when the nuclear envelope breaks down during mitosis.
Cis- and trans-acting factors affecting the structure of yeast centromeres
Authors: Bloom Kerry , Kenna Margaret , Saunders Michael 
Published: May 2013

ABSTRACT
The isolation of yeast centromeres has provided the opportunity to describe the molecular structure of chromosome attachments to the mitotic spindle. Nucleolytic probes of chromatin structure and analysis of genetically altered centromeres have been used to determine the primary sequence and positional requirements for assembly of this chromosomal domain into a functional unit. Structural analysis of the centromere in wild-type and mutant strains provides the first indication of specific proteins associated with centromere DNA in vivo.
Fission yeast cyclin: subcellular localisation and cell cycle regulation
Authors: Alfa Caroline E. , Booher Robert , Beach David , Hyams Jeremy S. 
Published: May 2013

ABSTRACT
Entry into mitosis in the fission yeast Schizosaccharomyces pombe involves the interaction of a number of genes with the major cell cycle control gene, cdc2+. One of these, cdcl3+, encodes a protein with homology to cyclin. By indirect immunofluorescence microscopy using antibodies to the appropriate bacterially-expressed protein, we have shown that both cdcl3 and cdc2 are nuclear proteins in S. pombe. Both are localised to a nuclear domain distinct from that occupied by the DAPI-staining chromatin. The immunofluorescence signals of both proteins show a progressive increase during interphase but are undetectable at mitosis. Loss of cdcl3 fluorescence at mitosis reflects the destruction of the protein. Thus, it behaves as a classic cyclin. This is not the case for cdc2, the level of which remains constant through the cell cycle. Cells carrying a disrupted copy of the cdcl3+ gene fail to accumulate either cdcl3 or cdc2 in the nucleus. Cells carrying a disrupted cdc2+ gene fail to accumulate cdc2 but reveal apparently normal levels of cdcl3. cdc13 therefore appears to be required to localise cdc2 to the nucleus but not vice versa. The destruction of cdcl3 at mitosis may allow cdc2 to redistribute to the cytoplasm.
Centrosomes and the cell cycle
Authors: Sluder Greenfield 
Published: May 2013

ABSTRACT
Centrosomes are the ensemble of organelles that form the poles of the mitotic spindle. We have examined the properties of the mechanisms that control the precise doubling, or reproduction, of centrosomes during the cell cycle. A functional analysis of this event in sea urchin eggs indicates that it is limited by the reproduction of determinants that we call polar organizers, around which the centrosome is organized. Each centrosome contains two polar organizers whose splitting, physical separation, and duplication control the reproduction of the centrosome. The splitting and duplication events are distinct processes that can be experimentally put out of phase with each other for several cell cycles. A serial section ultrastructural analysis of centrosomes with altered reproduction shows that the reproductive capacity of a centrosome is correlated with the number of centrioles it contains. In other experiments we show that centrosome reproduction is cytoplasmi- cally controlled; centrosomes repeatedly double in a normal fashion in physically enucleated sea urchin eggs and eggs in which DNA synthesis has been inhibited by aphidicolin. In addition, we show that centrosomes, through the spindle microtubules they nucleate, play an important role in the mechanisms that control the timing of mitotic events and the overall duration of the cell cycle. Taken together, our observations in concert with those of others suggest that the cell cycle is a cytoplasmic phenomenon that does not require nuclear activities for cells that are not growthlimited.
Mitosis in Drosophila development
Authors: Glover D. M. , Alphey L. , Axton J. M. , Cheshire A. , Dalby B. , Freeman M. , Girdham C. , Gonzalez C. , Karess R. E. , Leibowitz M. H. , Llamazares S. , Maldonado-Codina M. G. , Raff J. W. , Saunders R. , Sunkelj C. E. , Whitfield W. G. F. 
Published: May 2013

ABSTRACT
Many aspects of the mitotic cycle can take place independently in syncytial Drosophila embryos. Embryos from females homozygous for the mutation gnu undergo rounds of DNA synthesis without nuclear division to produce giant nuclei, and at the same time show many cycles of centrosome replication (Freeman et al. 1986). S phase can be inhibited in wild-type Drosophila embryos by injecting aphidicolin, in which case not only do centrosomes replicate, but chromosomes continue to condense and decondense, the nuclear envelope undergoes cycles of breakdown and reformation, and cycles of budding activity continue at the cortex of the embryo (Raff and Glover, 1988). If aphidicolin is injected when nuclei are in the interior of the embryo, centrosomes dissociate from the nuclei and can migrate to the cortex. Pole cells without nuclei then form around those centrosomes that reach the posterior pole (Raff and Glover, 1989); the centrosomes presumably must interact with polar granules, the maternally-provided determinants for pole cell formation. The pole cells form the germ-line of the developing organism, and as such may have specific requirements for mitotic cell division. This is suggested by our finding that a specific class of cyclin mRNAs, the products of the cyclin B gene, accumulate in pole cells during embryogenesis (Whitfield et al. 1989). Other genes that are essential for mitosis in early embryogenesis and in later development are discussed.
Maturation-promoting factor and the regulation of the cell cycle
Authors: Maller James L. , Gautier Jean , Langan Thomas A. , Lohka Manfred J. , Shenoy Suresh , Shalloway David , Nurse Paul 
Published: May 2013

ABSTRACT
Maturation-promoting factor (MPF) is a cell cycle control element able to cause metaphase when injected into amphibian oocytes or when incubated with nuclei in a cell-free system. Highly purified MPF consists of a complex between a 34K (K = 103Mr) serineμhreonine protein kinase, identified as a Xenopus homolog of the cdc2+ gene product, p34edc2, and a 45K substrate, identified as a Xenopus B-type cyclin. p34cdc2 is also present in purified preparations of chromatin-derived growth-associated histone Hl kinase from Novikoff hepatoma cells. p34ede2 is active when dephosphorylated and inactive when phosphorylated during oocyte meiotic cell cycles and in mitotic cell cycles following egg activation. Analysis of the substrate specificity of p34cdc2 indicates a consensus sequence for phosphorylation of (K/R)S/yP(X)K/R. Among substrates identified with this consensus are histone Hl and the pp60csrc proto-oncogene, which is known to be activated and phophorylated in mitosis. MPF injection into oocytes activates ribosomal protein S6 kinase II, which is also a lamin kinase. The mechanism of activation is indirect, possibly involving the c-src proto-oncogene. Continued analysis of regulation of MPF activation/inactivation and characterization of substrates for phosphorylation will have important implications for cell cycle and cell growth control.
Cyclin synthesis and degradation and the embryonic cell cycle
Authors: Murray Andrew W. 
Published: May 2013

ABSTRACT
I discuss recent advances in the study of somatic and embryonic cell cycles. In the frog embryonic cell cycle, cyclin is the only newly synthesized protein required to activate maturation-promoting factor and induce mitosis. Diminishing the rate of cyclin synthesis increases the length of interphase. Cyclin degradation is required for the progression from mitosis to interphase. Comparison of the frog embryonic cell cycle to other cell cycles suggests that all cell cycles will rely on the same closely conserved set of components. However, the component that is rate-limiting for any step in the cell cycle will vary in different cell cycles.
Retinoic acid and limb regeneration
Authors: Brockes Jeremy P. 
Published: May 2013

ABSTRACT
A key problem in the study of vertebrate development is to determine the molecular basis of positional value along a developmental axis. In amphibian regeneration, retinoic acid is able to respecify positional value in a graded fashion that is dependent on its concentration. In view of the fact that retinoic acid is a naturally occurring metabolite of vitamin A, this raises the possibility that it is deployed in vivo as an endogenous morphogen. Furthermore, the recent evidence that its effects are mediated by nuclear receptors of the steroid/thyroid hormone superfamily suggests the possibility of understanding the mechanism of its graded effects on morphogenesis. Such insights would be of crucial importance for our understanding of vertebrate patterning along an axis.
Signals in limb development: STOP, GO, STAY and POSITION
Authors: Wolpert Lewis 
Published: May 2013

ABSTRACT
Cell-to-cell interactions in early limb development are considered within the framework of the extracellular signals STOP, GO, STAY and POSITION, a classification which emphasises that the signals are elective rather than instructive, and that complexity arises from cells’ response. Patterning in the limb is analysed in terms of signals that specify positional values along the anteroposterior axes, and retinoic acid is thought to be a positional morphogen. There is however, evidence for patterning which does not depend on a positional signal. In the early bud the mesenchyme gives POSITION signals to the apical ridge, which in turn provides a STAY signal to the mesenchyme in the progress zone. Non-ridge ectoderm produces a STOP signal with respect to cartilage differentiation. The pattern of cartilage differentiation is specified well before cartilage condensation. Growth factors affect both cartilage and muscle differentiation in culture. Pigment patterns result from feather germs providing STOP or GO signals to the melanoblasts which enter all feather germs. The pathways for the cell-to-cell signals are not known but may involve gap junctions.
The structure of tumour necrosis factor - implications for biological function
Authors: Jones E. Y. , Stuart D. I. , Walker N. P. C. 
Published: May 2013

ABSTRACT
The three-dimensional structure of TNF has been determined at 0.29 nm using the technique of X-ray crystallography. Published data on site-directed mutagenesis and antibody binding may now be assessed in the light of the structure, thus the links between structure and function for TNF may be addressed.
TNF is a compact trimer composed of three identical subunits of 157 amino acids. The main-chain topology for a single subunit is essentially a β-sandwich structure formed by two anti-parallel β-pleated sheets. This mainchain fold corresponds to the ‘jelly roll’ motif observed in viral coat proteins such as VP1, VP2 and VP3 of rhinovirus, or the hemagglutinin molecule of influenza. TNF is the first non-viral protein to contain this motif. The subunits associate tightly about a threefold axis interacting through a simple edge-to-face packing of the β-sandwich to form the solid, conical shaped trimer. A large number of the residues conserved between the amino acid sequences of TNF and lymphotoxin lie within the β-sandwich or at the threefold axis of the trimer. This implies the presence of the same β-sandwich motif in the lymphotoxin monomer and preservation of the edge-to-face mode of trimeric association.
The detailed three dimensional structure for TNF explains a wide range of observations, including data on antibody binding and site directed mutagenesis. The currently available evidence points to a region of biological importance situated at the interface between two subunits on the lower half of the trimer.
X-ray crystallographic studies on murine nerve growth factor
Authors: Mcdonald N. Q. , Lapatto R. , Murray-Rust J. , Blundell T. L. 
Published: May 2013

ABSTRACT
The largest and best characterised family of neurotrophic growth factors is that of nerve growth factor (NGF) and its relatives. In order to understand the relation of structure and function, we have undertaken X-ray analyses of murine NGF. The active component β-NGF crystallises as hexagonal bipyramids that give good X-ray diffraction data using a synchrotron to 2.3Å resolution. We have prepared several heavy atom derivatives that are being used in the method of multiple isomorphous replacement to solve the phase problem and determine the three-dimensional structure. We have also prepared crystals of the precursor, 7S NGF, which is a complex of three different subunits of composition α2 β2 γ2We have collected X-ray data to 3Å resolution on two crystal forms with related cell dimensions and orthorhombic spacegroups. Detailed analyses of the structures of NGF in these crystal forms, taken together with data on sequence and biological activity, should give clues concerning the role of the precursor complex in storage and assist the identification of the surface region involved in receptor binding.
Chimeric molecules map and dissociate the potent transforming and secretory properties of PDGF A and PDGF B
Authors: Larochelle William J. , Giese Neill , May-Siroff Mary , Robbins Keith C. , Aaronson Stuart A. 
Published: May 2013

ABSTRACT
Human platelet-derived growth factor (PDGF) is a connective tissue cell mitogen comprising two related chains encoded by distinct genes. The B chain is the homolog of the v-sis oncogene product. Properties that distinguish these ligands include greater transforming potency of the B chain and more efficient secretion of the A chain. By a strategy involving the generation of PDGF A and B chimeras, these properties were mapped to distinct domains of the respective molecules. Increased transforming efficiency segregated with the ability to activate both alpha and beta PDGF receptors. These findings genetically map PDGF B residues 105 to 144 as responsible for conformational alterations critical to beta PDGF receptor interaction, and provide a mechanistic basis for the greater transforming potency of the PDGF B chain.
Effect of MAP2, MAP2c, and tau on kinesin-dependent microtubule motility
Authors: Heins Susanne , Song Young-Hwa , Wille Holger , Mandelkow Eckhard , Mandelkow Eva-Maria 
Published: May 2013

ABSTRACT
By making use of DIC video microscopy to monitor microtubule motility we have studied the effect of several MAPs (MAP2, MAP2c, tau) on microtubule-kinesin interactions and microtubule gliding. Of the three MAPs tested, MAP2 interferes most strongly with kinesin-dependent microtubule motility.