bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison Of Spindle Elongation In Vivo And In Vitro In Stephanopyxis Turris
Authors: L. Mcdonald K. , Pfister K. , Masuda H. , Wordeman L. , Staiger C. , Z. Cande W. 
Published: May 2013

ABSTRACT
The spindle in dividing cells of the diatom Stephanopyxis turris contains three distinct classes of microtubules: central spindle microtubules, which slide over each other and grow during anaphase spindle elongation; kinetochore-attached microtubules, which are located on the outer surface of the central spindle; and peripheral microtubules, which fan out from the spindle poles in astral-like arrays. The poles are multilayered structures, which remain attached to the spindle after isolation. In vitro, after addition of ATP, central spindles elongate and the two half-spindles slide completely apart with a concurrent decrease in the extent and magnitude of the zone of microtubule overlap. Spindle elongation takes place in spindles whose chromatin has been removed by enzymic digestion and the extent of elongation in vitro is increased by the addition of neurotubulin. After ATP addition the arrays of interdigitating microtubules in the zone of overlap become disordered and selectively depolymerize from the overlap zone polewards. In some reactivated spindles an unusual structure, a striated fibre, can be seen running from the pole plates part of the way towards the spindle midzone. The fibre has no precedent in mitotic ultrastructure and its function is unclear. These results demonstrate that we can duplicate the essential elements of anaphase B in vitro and that this system will be useful for further studies of the molecular basis of spindle elongation.
Tubulin Isotypes: Generation Of Diversity In Cells And Microtubular Organelles
Authors: Gull K. , J. Hussey P. , Sasse R. , Schneider A. , Seebeck T. , Sherwin T. 
Published: May 2013

ABSTRACT
Diversity of tubulin isotypes is illustrated by consideration of the β-tubulin isotypes of higher plants and the eukaryotic microbe, Physarum polycephalum, and by the α-tubulin isotypes of the protozoan, Trypanosoma brucei. The carrot plant expresses six, well-defined β-tubulin isotypes that possess characteristic two-dimensional gel coordinates. These six β-tubulin isotypes are differentially expressed during development of the flowering plant. In a similar manner, Physarum expresses three separate)3-tubulin isotypes during its life cycle; of the two β; isotypes, one is expressed solely in the myxamoeba whilst the other is expressed both in the myxamoeba and in the plasmodium. A further i8-tubulin isotype, β;2, is expressed only in the plasmodium. In carrot and in Physarum the generation of β;-tubulin diversity appears, in the main, to be generated by the differential expression of a β-tubulin multi-gene family. However, tubulin isotypes can also be generated by post-translational modifications and T. brucei utilizes two different modifications within one cell. First, the primary translation product, the αl-tubulin isotype, can be acetylated to produce the α3 isotype. Second, both the al and a) isotypes appear to exist in both tyrosinated and detyrosinated forms. The generation of these α-tubulin isotypes within the same cell and their presence in particular cellular domains, modulated throughout the cell cycle, reveals a complex relationship between α-tubulin isotypes produced by post-translational modifications and the dynamics of microtubule construction.
Intermediate Filament Networks: Organization And Possible Functions Of A Diverse Group Of Cytoskeletal Elements
Authors: D. Goldman Robert , E. Goldman Anne , J. Green Kathleen , C. R. Jones Jonathan , M. Jones Stephanie , Yang Hsi-Yuan 
Published: May 2013

ABSTRACT
Immunofluorescence and electron microscopic observations demonstrate that intermediate filaments (IF) form cytoplasmic networks between the nucleus and cell surface in several types of cultured cells. Intermediate filaments interact with the nuclear surface, where they appear to terminate at the level of the nuclear envelope. From this region, they radiate towards the cell surface where they are closely associated with the plasma membrane. On the basis of these patterns of IF organization, we suggest that IF represent a cytoskeletal system interconnecting the cell surface with the nucleus. Furthermore, IF also appear to interact with other cytoskeletal components including microtubules and microfilaments. In the former case microtubule-IF interactions are seen in cytoplasmic regions between the nucleus and the cell membrane, whereas microfilament—IF interactions occur in the cortical cytoplasm. IF also appear to be cross-linked to each other; especially in the case of the IF bundles that occur in epithelial cells. In order to determine the molecular and biochemical bases of the organizational state of IF we have developed procedures for obtaining IF–enriched ‘cytoskeletons’ of cultured cells. In these preparations IF–nuclear and IF–cell surface associations are retained. Thus, these preparations have enabled us to begin to study various IFassociated structures (e.g. desmosomes) and associated proteins (IFAPs) using biochemical and immunological methodologies. To date, the results support the idea that IF and their associated proteins may comprise the cell type specific molecular infrastructure that is involved in transmitting and distributing information amongst the major cellular domains; the cell surface/extracellular matrix, the cytoplasm and the nuclear surface/nuclear matrix.
Association Of Rna With The Cytoskeleton And The Nuclear Matrix
Authors: G. Fey Edward , A. Ornelles David , Penman Sheldon 
Published: May 2013

ABSTRACT
Heteronuciear RNA (hnRNA) is preferentially associated (76%) with the nuclear matrix in mammalian cells. Active mRNA, in the form of polyribosomes, is associated (&gt;97%) with the cytoskeletal framework. In this report, we present evidence that the association of both hnRNA and mRNA with structural networks of the cell may be essential features of gene expression.
To study the association of polyribosomes with the cytoskeletal framework, cytochalasin D was used to release mRNA from the cytoskeletal framework. Protein synthesis was inhibited by cytochalasin D in direct proportion to the release of mRNA. The released mRNA is unaltered in its translatability as measured in vitro but is no longer translated in the cytochalasin-treated HeLa cells. The residual protein synthesis occurs on polyribosomes that are reduced in amount but display a normal sedimentation distribution. The results support the hypothesis that mRNA binding to the cytoskeletal framework is necessary, though not sufficient, for translation.
Further fractionation of the cytoskeletal framework separates nuclear constituents into three distinct protein fractions. Chromatin proteins and 94% of the DNA are released by 0-25?- ammonium sulphate after inter-nucleosomal DNA is cut with DNase I. The resulting structure retains 76% of the hnRNA in the form of ribonucleoprotein and is designated the RNP-containing nuclear matrix. The proteins of hnRNP complex are those associated with the nucleus only if RNA is intact. These proteins and 97% of the hnRNA are released after brief digestion with RNase A.
Visualizing the nuclear matrix using resinless sections shows that nuclear RNA plays an important role in the organization of the nuclear matrix. Electron micrographs of resinless sections show the interior of the matrix to be a three-dimensional network of thick filaments bounded by the nuclear lamina. The filaments are densely covered with 20-30 nm electron-dense particles, which may contain the hnRNA. The RNP-depleted matrix is disordered and the interior fibres aggregated. These results suggest that hnRNA is involved in the spatial organization of the interior of the nuclear matrix.
Plant transposable elements and their role in the evolution of regulatory units and proteins
Authors: Saedler Heinz , Gierl Alfons , Sommer Hans , Schwarz-Sommer Zsuzsanna 
Published: May 2013

ABSTRACT
Transposable elements (TE) are natural constituents of plant genomes. However, their presence becomes only apparent if they become dislodged from their resident positions in the genome and transpose into another gene thereby inducing a mutation. Such TE-induced mutations are somatically unstable because they revert to wild type and hence reconstitute the expression of the mutated gene. The frequent somatic excision of the TE results in a variegated phenotype. Since this instability is inherited in a Mendelian manner the variegated phenotype is nuclear determined. By this criterion TE have been shown to occur in more than 30 species belonging to different families and genera (Nevers et al. 1986).
Many questions arise when dealing with TE, concerning, for example, their structure and functions but also concerning the biological significance of the activity of elements in the differentiation of a normal plant or in the evolution of plant genes.
In an attempt to answer these questions we will deal with one of the many TEs of Zea mays, the En/l or Spm systems and will include briefly Taml, one of the three systems of Antirrhinum majus.
The genetic organization of the yeast ty element
Authors: Kingsman Alan J. , Mellor Jane , Adams Sally , Rathjen Peter D. , Malim Michael H. , Fulton Sandra M. , Wilson Wilma , Kingsman Susan M. 
Published: May 2013

ABSTRACT
The genetic organization of the yeast transposon Ty resembles that of higher eukaryotic retroviruses and other elements such as the copia-like sequences of Drosophila. The Ty genome is 5·9 kb (103 bases) long. It has 340 bp (base pairs) terminal repeats known as delta sequences and it produces a terminally redundant 5·7kb RNA that starts in the 5’ delta and ends in the 3′ delta. Ty transcription is directed by signals upstream and downstream of the major RNA start site and is regulated by the mating-type configuration of the cell. The 5·7 kb transcriptional unit is divided into two overlapping open reading frames, TYA and TYB. TYA occupies approximately the first quarter of the transcriptional unit while TYB occupies the rest. TYB overlaps TYA by either 38 or 44 nucleotides, depending on the element, and is in the plus one reading frame with respect to TYA. TYA is expressed to produce protein pl (50×103Mr) and TYB is expressed as a fusion protein, p3 (190× 103Mr,). Both of these proteins are subsequently cleaved to produce proteins p2, p4, p5, p6, reverse transcriptase and a protease that is responsible for some of these cleavage events. These proteins are assembled into virus-like particles (Ty-VLPs) that contain Ty RNA and reverse transcriptase activity. It is likely that the Ty-VLPs are units of transposition as Ty transposes via an RNA intermediate.
The hepatitis-b viruses: molecular biology and recent tissue culture systems
Authors: üRgen Schlicht Hans-J , Galle Peter , SCHALLER Heinz 
Published: May 2013

ABSTRACT
In this report we summarize what is known about the molecular biology of the hepatitis-B viruses. In the first part we describe the general properties of these viruses, their structure and their replication strategy. In the second part we discuss the most recent attempts at the establishment of tissue culture systems allowing the study of the virus/host cell interactions in vitro. In addition we present experimental data from our laboratory in which we show that new synthesis of viral proteins can be studied in vitro either by biochemical analysis of already infected cells or after experimental infection.
Structure and replication of caulimovirus genomes
Authors: HULL R. , Covey S. N. , Maule A. J. 
Published: May 2013

ABSTRACT
In this paper the current state of knowledge of the replication of cauliflower mosaic virus (CaMV) is reviewed and the DNA intermediates and enzymes involved in replication are discussed. Based on this information a model for the replication complex is developed. In this model it is suggested that replication complexes resemble virus particles and that, in their assembly, there are close interactions between the inclusion body protein, the virus coat protein, the replicase enzyme, the tRNA primer and the 35S RNA template. The similarities between CaMV replication complexes and those of retroviruses are discussed, and we extend this discussion to a comparison between CaMV and reverse transcribing elements.
Replication of the genome of alphaviruses
Authors: Kääriäinen Leevi , Takkinen Kristiina , Keränen Sirkka , Söderlund Hans 
Published: May 2013

ABSTRACT
The genome of Semliki Forest virus (SFV) is 11 442 nucleotides with a 5′ cap-structure and a 3′ poly(A) tail of about 100 residues. The genome of the closely related Sindbis virus (SIN) is slightly longer (11 703 nucleotides). The parental RNA is first translated from the 5′ two thirds to yield; nsPl, nsP2, nsP3 and nsP4, which are cleaved from a polyprotein of 2431 amino acids (SFV). The parental genome is copied to a full-length minus strand with poly(U) at the 5′ end. The minus strand is used as template for the synthesis of 42 S RNA in membrane-bound replicative intermediate (RI) structures. In addition to 42 S RNA, a 3′-coterminal subgenomic 26 S mRNA, coding for the structural proteins, is synthesized by internal initiation at the minus strand. Capping and methylation of both plus-strand RNAs occur concomitantly with their synthesis.
Analysis of Sindbis virus temperature-sensitive RNA-negative mutants have shown that one complementation group (B) is specifically associated with the synthesis of minus strands. Another, group F, is involved in the polymerization step of both minus- and plus-strand 42 S RNA, and of the 26 S mRNA. The synthesis of minus strands is normally dependent on protein synthesis. There is a shut off of the minus-strand RNA synthesis at about 3h post-infection. This is apparently regulated by a virus-specific protein, represented by the complementation group A. The same protein is involved in the regulation of the initiation of 26 S RNA together with a component represented by group G mutants. Comparative analysis of SFV and SIN RNAs and DI RNAs of both viruses suggests that perhaps only 19 nucleotides from the 3′ end and about 150 nucleotides from the 5’ end are needed for replication of the alphavirus RNAs. In some SIN DI RNAs the proposed secondary structure at the 5’ end is replaced by a cellular tRNAASP suggesting that the secondary structure rather than nucleotide sequence is sufficient for the recognition by the viral polymerase.
Even when the primary structure of the four non-structural proteins of both SFV and SIN is known, the correlation of the genetic data with the individual proteins has not yet been possible.
Self-cleavage of rna in the replication of viroids and virusoids
Authors: Symons Robert H. , Hutchins Cheryl J. , Forster Anthony C. , Rathjen Peter D. , Keese Paul , Visvader Jane E. 
Published: May 2013

ABSTRACT
Viroids are infectious, circular RNA molecules of 246 to 375 nucleotides found in plants. Virusoids are of similar size and structure but they are dependent on, and encapsidated in, a helper virus. A rolling circle mechanism of replication is considered to account for the presence of greater-than-unit-length plus and minus RNAs of both viroids and virusoids found in infected plants. An essential feature of this mechanism is the specific processing or cleavage of high molecular weight intermediates to produce linear monomers which are then ligated to circular monomers.
We have investigated the putative processing cleavage reactions using in vitro-synthesized RNA transcripts of dimeric cDNA clones of the 247-nucleotide avocado sunblotch viroid (ASBV) and of partial cDNA clones of the 324-nucleotide virusoid of lucerne transient streak virus (vLTSV). In both cases, there is a specific, non-enzymic, self-cleavage of plus as well as minus transcripts. The plus and minus sites of cleavage are in neighbouring parts of ASBV and of vLTSV and highly conserved two-dimensional structures can be drawn around the cleavage sites as well as around the putative or demonstrated cleavage sites of precursors of the virusoids of three other viruses and of the linear satellite RNA of tobacco ringspot virus. The results also indicate that the sole function of about one-third of the ASBV and vLTSV molecules is provision of sequences that allow the formation of the self-cleavage structures of both ‘plus’ and ‘minus’ RNA precursors during the replication cycle.
Similar self-cleavage of ‘plus’ RNA transcripts of a dimeric cDNA clone of citrus exocortis virus (CEV) was not observed. However, the putative processing site for CEV precursors was located within three nucleotides by site-directed mutagenesis. No two-dimensional structures similar to those found for ASBV and vLTSV were found around the processing site. It is possible that a different type of self-cleavage or enzymic processing event occurs during the replication cycle of CEV and related viroids.
The genome of herpes simplex virus: structure, replication and evolution
Authors: Mcgeoch Duncan J. 
Published: May 2013

ABSTRACT
The objectives of this paper are to discuss the structure and genetic content of the genome of herpes simplex virus type 1 (HSV-1), the nature of virus DNA replicative processes, and aspects of the evolution of the virus DNA, in particular those bearing on DNA replication. We are in the late stages of determining the complete sequence of the DNA of HSV-1, which contains about 155 000 base pairs, and thus the treatment is primarily from a viewpoint of DNA sequence and organization.
The genome possesses around 75 genes, generally densely arranged and without long range ordering. Introns are present in only a few genes. Protein coding sequences have been predicted, and the functions of the proteins are being pursued by various means, including use of existing genetic and biochemical data, computer based analyses, expression of isolated genes and use of oligopeptide antisera. Many proteins are known to be virion structural components, or to have regulatory roles, or to function in synthesis of virus DNA. Many, however, still lack an assigned function.
Two classes of genetic entities necessary for virus DNA replication have been characterized: cisacting sequences, which include origins of replication and packaging signals, and genes encoding proteins involved in replication. Aside from enzymes of nucleotide metabolism, the latter include DNA polymerase, DNA binding proteins, and five species detected by genetic assays, but of presently unknown functions.
Complete genome sequences are now known for the related alphaherpesvirus varicella-zoster virus and for the very distinct gammaherpesvirus Epstein-Barr virus. Comparisons between the three sequences show various homologies, and also several types of divergence and rearrangement, and so allow models to be proposed for possible events in the evolution of present day herpesvirus genomes. Another aspect of genome evolution is seen in the wide range of overall base compositions found in present day herpesvirus DNAs. Finally, certain herpesvirus genes are homologous to nonherpesvirus genes, giving a glimpse of more remote relationships.
Activation of Keratinocyte Fibronectin Receptor Function During Cutaneous Wound Healing
Authors: Grinnell Frederick , Toda Ken-Ichi , Takashima Akira 
Published: May 2013

ABSTRACT
Keratinocytes freshly isolated from unwounded skin could not attach and spread on fibronectin (FN)-coated culture dishes and could not bind and phagocytose FN-coated beads. These adhesive functions were activated, however, in Keratinocytes that were isolated from healing wounds. Moreover, adhesiveness of basal Keratinocytes to FN substrata was activated during epidermal cell or explant culture. Activation was specific for attachment to FN compared to other adhesion ligands, and occurred even when epidermal cells were cultured on collagen, basement membrane matrix, or lectin-coated substrata. Biochemical studies showed that Keratinocytes have a 140× 103Mr FN receptor analogous to the fibroblast receptor for FN, and that this receptor is expressed in activated Keratinocytes but not in Keratinocytes freshly isolated from unwounded skin. The absence of FN receptors from Keratinocytes in unwounded skin is not surprising since the basal Keratinocytes of the epidermis are attached to a basement membrane containing laminin and type IV collagen. During wound repair, however, these cells migrate over or through a FN-coated matrix. Consequently, expression of FN receptors may be an essential feature of healing. Believing that FN is the required substratum for keratinocyte migration during wound healing, we have initiated clinical studies to determine if topical application of FN is useful as a therapy for non-healing cutaneous ulcers.
Adhesive Interactions and the Metabolic Activity of Hepatocytes
Authors: Hughes R. Colin , Stamatoglou Stamatis C. 
Published: May 2013

ABSTRACT
The nature and influence of adhesive interactions of rat hepatocytes with components of the extracellular matrix has been studied in culture. Hepatocytes interact with different kinetics to substrata composed of collagen type IV, laminin or fibronectin and adopt significantly different morphologies. The receptors mediating these various responses appear to be specific, according to the matrix, and in the case of fibronectin are complex, implicating several components of the hepatocyte surface. Collagen type IV maintains a differentiated phenotype more efficiently than fibronectin or laminin as measured by the production of adult hepatocyte markers such as albumin and repression of a-foetoprotein synthesis. Formation of matrix components is also influenced by the substratum: synthesis and secretion of fibronectin or collagen type IV is down-regulated when cells are cultured on the homologous substratum. Hepatocytes cultured in vitro secrete components of the coagulation cascade and also mediate fibrinolysis on addition of exogenous plasmin. The results are discussed in relation to the normal phenotype of the mature hepatocyte in vivo.
Influence of Cell Shape and Adhesiveness On Stratification and Terminal Differentiation of Human Keratinocytes in Culture
Authors: WATT FIONA M. 
Published: May 2013

ABSTRACT
Human epidermal keratinocytes can be grown in culture under conditions in which they assemble a tissue with the same basic organization as normal epidermis. The cells stratify, mitosis is restricted to the basal layer and terminal differentiation occurs as the cells move through the suprabasal layers. Keratinocytes do not have to leave the basal layer in order to undergo terminal differentiation, but the two processes are normally linked, because during terminal differentiation the adhesive affinity of keratinocytes for the culture substratum and for other keratinocytes is reduced. Down-regulation of synthesis of basement membrane components and their receptors may provide the molecular basis for the reduction in cell-substratum adhesiveness. However, the molecules that mediate changes in cohesiveness have not yet been identified. Restriction of substratum contact, so that cells are prevented from spreading, appears to be one signal that induces keratinocytes to stop dividing and undergo terminal differentiation.
Studies on The Migration of Mouse Germ Cells
Authors: Donovan Peter J. , Stott David , Godin Isabelle , Heasman Janet , Wylie Christopher C. 
Published: May 2013

ABSTRACT
Primordial germ cells in the mouse embryo migrate from their site of origin to the gonad where they differentiate, giving rise eventually to the gametes of the mature adult animal. The migratory phase is transient and therefore permits analysis of factors regulating the motile activity of cells in tissues. Germ cells can be isolated during migration and cultured on feeder cells of an established cell line (STO). In this system the molecular interactions mediating germ cell adhesion can be probed using antibodies to both germ cell surface determinants and to extracellular matrix components.