The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
George Miller - One of the best experts on this subject based on the ideXlab platform.
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Nuclear Translocation and Regulation of Intranuclear Distribution of Cytoplasmic Poly(A)-Binding Protein Are Distinct Processes Mediated by Two Epstein Barr Virus Proteins
2016Co-Authors: Richard Park, Ayman El-guindy, Lee Heston, Su-fang Lin, Mate Nagy, Sumit Borah, Henri-jacques Delecluse, Joan Steitz, George MillerAbstract:Many viruses target cytoplasmic polyA binding protein (PABPC) to effect widespread inhibition of host gene expression, a process termed viral host-shutoff (vhs). During lytic replication of Epstein Barr Virus (EBV) we observed that PABPC was efficiently translocated from the cytoplasm to the nucleus. Translocated PABPC was diffusely distributed but was excluded from viral replication compartments. Vhs during EBV infection is regulated by the viral alkaline nuclease, BGLF5. Transfection of BGLF5 alone into BGLF5-KO cells or uninfected 293 cells promoted translocation of PAPBC that was distributed in clumps in the nucleus. Zebra, a viral bZIP protein, performs essential functions in the lytic program of EBV, including activation or repression of downstream viral genes. Zebra is also an essential replication protein that binds to viral oriLyt and interacts with other viral replication proteins. We report that Zebra also functions as a regulator of vhs. Zebra translocated PABPC to the nucleus, controlled the intranuclear distribution of PABPC, and caused global shutoff of host gene expression. Transfection of Zebra alone into 293 cells caused nuclear translocation of PABPC in the majority of cells in which Zebra wa
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A Subset of Replication Proteins Enhances Origin Recognition and Lytic Replication by the Epstein-Barr Virus Zebra Protein
2010Co-Authors: Ayman El-guindy, Lee Heston, George MillerAbstract:Zebra is a site-specific DNA binding protein that functions as a transcriptional activator and as an origin binding protein. Both activities require that Zebra recognizes DNA motifs that are scattered along the viral genome. The mechanism by which Zebra discriminates between the origin of lytic replication and promoters of EBV early genes is not well understood. We explored the hypothesis that activation of replication requires stronger association between Zebra and DNA than does transcription. A Zebra mutant, Z(S173A), at a phosphorylation site and three point mutants in the DNA recognition domain of Zebra, namely Z(Y180E), Z(R187K) and Z(K188A), were similarly deficient at activating lytic DNA replication and expression of late gene expression but were competent to activate transcription of viral early lytic genes. These mutants all exhibited reduced capacity to interact with DNA as assessed by EMSA, ChIP and an in vivo biotinylated DNA pull-down assay. Over-expression of three virally encoded replication proteins, namely the primase (BSLF1), the single-stranded DNAbinding protein (BALF2) and the DNA polymerase processivity factor (BMRF1), partially rescued the replication defect in these mutants and enhanced Zebra’s interaction with oriLyt. The findings demonstrate a functional role of replication proteins in stabilizing the association of Zebra with viral DNA. Enhanced binding of Zebra to oriLyt is crucial for lytic vira
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Phosphorylation of Epstein-Barr virus Zebra protein at its casein kinase 2 sites mediates its ability to repress activation of a viral lytic cycle late gene by Rta.
Journal of virology, 2004Co-Authors: Ayman El-guindy, George MillerAbstract:Zebra, a member of the bZIP family, serves as a master switch between latent and lytic cycle Epstein-Barr virus (EBV) gene expression. Zebra influences the activity of another viral transactivator, Rta, in a gene-specific manner. Some early lytic cycle genes, such as BMRF1, are activated in synergy by Zebra and Rta. However, Zebra suppresses Rta's ability to activate a late gene, BLRF2. Here we show that this repressive activity is dependent on the phosphorylation state of Zebra. We find that two residues of Zebra, S167 and S173, that are phosphorylated by casein kinase 2 (CK2) in vitro are also phosphorylated in vivo. Inhibition of Zebra phosphorylation at the CK2 substrate motif, either by serine-to-alanine substitutions or by use of a specific inhibitor of CK2, abolished Zebra's capacity to repress Rta activation of the BLRF2 gene, but did not alter its ability to initiate the lytic cycle or to synergize with Rta in activation of the BMRF1 early-lytic-cycle gene. These studies illustrate how the phosphorylation state of a transcriptional activator can modulate its behavior as an activator or repressor of gene expression. Phosphorylation of Zebra at its CK2 sites is likely to play an essential role in proper temporal control of the EBV lytic life cycle.
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Role of the Epstein-Barr Virus Rta Protein in Activation of Distinct Classes of Viral Lytic Cycle Genes
Journal of virology, 1999Co-Authors: Tobias Ragoczy, George MillerAbstract:Initiation of the Epstein-Barr virus (EBV) lytic cycle is controlled by two immediate-early genes, BZLF1 and BRLF1. In certain epithelial and B-cell lines, their protein products, Zebra and Rta, stimulate their own expression, reciprocally stimulate each other’s expression, and activate downstream viral targets. It has been difficult to examine the individual roles of these two transactivators in EBV-infected lymphocytes, as they are expressed simultaneously upon induction of the lytic cycle. Here we show that the Burkitt lymphoma cell line Raji represents an experimental system that allows the study of Rta’s role in the lytic cycle of EBV in the absence and presence of Zebra. When expressed in Raji cells, exogenous Rta does not activate endogenous BZLF1 expression, yet Rta remains competent to transactivate certain downstream viral targets. Some genes, such as BaRF1, BMLF1, and a late gene, BLRF2, are maximally activated by Rta itself in the absence of detectable Zebra. The use of the Z(S186A) mutant form of Zebra, whose transactivation function is manifest only by coexpression of Rta, allows identification of a second class of lytic cycle genes, such as BMRF1 and BHRF1, that are activated in synergy by Rta and Zebra. It has already been documented that of the two activators, only Zebra stimulates the BRLF1 gene in Raji cells. Thus, there is a third class of viral genes activated by Zebra but not Rta. Moreover, Zebra exhibits an inhibitory effect on Rta’s capacity to stimulate the late gene, BLRF2. Consequently Zebra may function to repress Rta’s potential to activate some late genes. Raji cells thus allow delineation of the combinatorial roles of Rta and Zebra in control of several distinct classes of lytic cycle genes.
Lars G Rudstam - One of the best experts on this subject based on the ideXlab platform.
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predation on invasive Zebra mussel dreissena polymorpha by pumpkinseed sunfish rusty crayfish and round goby
Hydrobiologia, 2014Co-Authors: Rahmat Naddafi, Lars G RudstamAbstract:The enemy release hypothesis states that invasive species are successful in their new environment because native species are not adapted to utilize the invasive. If true for predators, native predators should have lower feeding rates on the invasive species than a predator from the native range of the invasive species. We tested this hypothesis for Zebra mussel (Dreissena polymorpha) by comparing handling time and predation rate on Zebra mussels in the laboratory by two North American species (pumpkinseed, Lepomis gibbosus, and rusty crayfish, Orconectes rusticus) and one predator with a long evolutionary history with Zebra mussels (round goby, Neogobius melanostomus). Handling time per mussel (7 mm shell length) ranged from 25 to >70 s for the three predator species. Feeding rates on attached Zebra mussels were higher for round goby than the two native predators. Medium and large gobies consumed 50–67 Zebra mussels attached to stones in 24 h, whereas pumpkinseed and rusty crayfish consumed <11. This supports the hypothesis that the rapid spread of Zebra mussels in North America was facilitated by low predation rates from the existing native predators. At these predation rates and realistic goby abundance estimates, round goby could affect Zebra mussel abundance in some lakes.
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response of yellow perch perca flavescens in oneida lake new york to the establishment of Zebra mussels dreissena polymorpha
Canadian Journal of Fisheries and Aquatic Sciences, 2000Co-Authors: Christine M Mayer, Lars G Rudstam, Anthony J Vandevalk, John L Forney, Edward L MillsAbstract:We used long-term data on Oneida Lake, New York, to evaluate hypotheses about the effects of introduced Zebra mussels (Dreissena polymorpha) on yellow perch (Perca flavescens). We detected no change in survival, diet, or numbers of young-of-the-year (YOY) yellow perch. YOY growth increased in association with Zebra mussel introduc- tion and was marginally correlated with zooplankton size, which increased after Zebra mussel introduction. Low num- bers of YOY in recent years did not explain their increased growth rate. The percentage of age 3 and older yellow perch that consumed zooplankton and benthos increased after Zebra mussel introduction. Water clarity, which has increased since Zebra mussel introduction, was inversely related to the percentage of the adult population with empty stomachs and positively related to the percentage that consumed benthos. The percentage of adult yellow perch that consumed zooplankton was positively related to zooplankton size. Despite the increase in percentage of adults consum- ing both types of invertebrate prey, we detected no changes in adult growth associated with Zebra mussel introduction. This suggests that the principal effects of Zebra mussels on yellow perch in Oneida Lake were not via benthic path- ways but through modifications of water clarity and zooplankton. Thus far, these effects have not been negative for the yellow perch population.
Daniel I. Rubenstein - One of the best experts on this subject based on the ideXlab platform.
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population structure inbreeding and stripe pattern abnormalities in plains Zebras
Molecular Ecology, 2021Co-Authors: Brenda Larison, Daniel I. Rubenstein, Christopher B Kaelin, Ryan J Harrigan, Corneliu Henegar, Pauline L Kamath, Ortwin Aschenborn, Thomas B Smith, Gregory S BarshAbstract:One of the most iconic wild equids, the plains Zebra occupies a broad region of sub-Saharan Africa and exhibits a wide range of phenotypic diversity in stripe patterns that have been used to classify multiple subspecies. After decades of relative stability, albeit with a loss of at least one recognized subspecies, the total population of plains Zebras has undergone an approximate 25% decline since 2002. Individuals with abnormal stripe patterns have been recognized in recent years but the extent to which their appearance is related to demography and/or genetics is unclear. Investigating population genetic health and genetic structure are essential for developing effective strategies for plains Zebra conservation. We collected DNA from 140 plains Zebra, including seven with abnormal stripe patterns, from nine locations across the range of plains Zebra, and analyzed data from restriction site-associated and whole genome sequencing (RAD-seq, WGS) libraries to better understand the relationships between population structure, genetic diversity, inbreeding, and abnormal phenotypes. We found that genetic structure did not coincide with described subspecific variation, but did distinguish geographic regions in which anthropogenic habitat fragmentation is associated with reduced gene flow and increased evidence of inbreeding, especially in certain parts of East Africa. Further, Zebras with abnormal striping exhibited increased levels of inbreeding relative to normally striped individuals from the same populations. Our results point to a genetic cause of stripe pattern abnormalities, and dramatic evidence of the consequences of habitat fragmentation.
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population structure inbreeding and stripe pattern abnormalities in plains Zebras
Molecular Ecology, 2020Co-Authors: Brenda Larison, Daniel I. Rubenstein, Christopher B Kaelin, Ryan J Harrigan, Corneliu Henegar, Pauline L Kamath, Ortwin Aschenborn, Thomas B Smith, Gregory S BarshAbstract:One of the most iconic wild equids, the plains Zebra occupies a broad region of sub-Saharan Africa and exhibits a wide range of phenotypic diversity in stripe patterns that have been used to classify multiple sub-species. After decades of relative stability, albeit with a loss of at least one recognized subspecies, the total population of plains Zebras has undergone an approximate 25% decline since 2002. Individuals with abnormal stripe patterns have been recognized in recent years but the extent to which their appearance is related to demography and/or genetics is unclear. Investigating population genetic health and genetic structure are essential for developing effective strategies for plains Zebra conservation. We collected DNA from 140 plains Zebra, including 7 with abnormal stripe patterns, from 9 locations across the range of plains Zebra, and analyzed data from restriction site-associated and whole genome sequencing (RAD-seq, WGS) libraries to better understand the relationships between population structure, genetic diversity, inbreeding, and abnormal phenotypes. We find that genetic structure does not coincide with described subspecific variation, but does distinguish geographic regions in which anthropogenic habitat fragmentation is associated with reduced gene flow and increased evidence of inbreeding, especially in certain parts of East Africa. Further, Zebras with abnormal striping exhibited increased levels of inbreeding relative to normally striped individuals from the same populations. Our results point to a genetic cause of stripe pattern abnormalities, and dramatic evidence of the consequences of habitat fragmentation.
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habitat choice of grevy s Zebras equus grevyi in laikipia kenya
African Journal of Ecology, 2008Co-Authors: Siva R Sundaresan, Ilya R Fischhoff, Helen M Hartung, Patrick Akilong, Daniel I. RubensteinAbstract:Characterizing habitat choice is essential for endangered species conservation. For the endangered Grevy’s Zebra (Equus grevyi), as with many widely ranging vertebrates, human activities may be an important factor affecting space use. Grevy’s Zebras are grazing ungulates inhabiting the savannahs of central-northern Kenya and Ethiopia. Past research on their social organization indicates that reproductive status shapes associations and movements. Here, we examine how habitat use varies across four reproductive classes: lactating and nonlactating females, bachelors and territorial males. We also test whether Grevy’s Zebra avoid locations close to active livestock corrals, or bomas. We find that forage quality, forage quantity and habitat openness of locations used by Grevy’s Zebra vary significantly depending on individual reproductive state. Lactating females and bachelors use areas with green, short grass and mediumdense bush more frequently than nonlactating females or territorial males. We hypothesize that lactating females trade off forage quantity and safety to access nutrients in growing grass. Across reproductive classes, Grevy’s Zebra choose locations further from active bomas than if they used the area randomly. Our results suggest that Grevy’s Zebra may require a range of vegetation characteristics for different reproductive classes. Further, they may need areas free from competition or disturbance by
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habitat use and movements of plains Zebra equus burchelli in response to predation danger from lions
Behavioral Ecology, 2007Co-Authors: Ilya R Fischhoff, Siva R Sundaresan, Justine E Cordingley, Daniel I. RubensteinAbstract:Prey species must adapt their behavior to avoid predation. As a key prey item for lions (Panthera leo), plains Zebras (Equus burchelli) were expected to respond to immediate threats posed by lions in their area. In addition, Zebras were predicted to exhibit behavior tuned to reduce the potential for encounters with lions, by modifying their movement patterns in the times of day and habitats of greatest lion danger. We studied a population of approximately 600 plains Zebra living in Ol Pejeta Conservancy, Kenya. We found that Zebra abundance on or near a grassland patch was lower if lions had also been observed on that patch during the same day. Predation danger was highest in grassland habitat during the night, when lions were more active. Zebra sightings and global positioning system radio collar data indicated that Zebras also reduced their use of grassland at night, instead using more woodland habitat. Zebras moved faster and took sharper turns in grassland at night. It is hypothesized that these more erratic movements assist Zebras in avoiding detection or capture by lions. Copyright 2007, Oxford University Press.
M Karlický - One of the best experts on this subject based on the ideXlab platform.
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brightness temperature of radio Zebras and wave energy densities in their sources
Solar Physics, 2017Co-Authors: L V Yasnov, Jan Benacek, M KarlickýAbstract:We estimated the brightness temperature of radio Zebras (Zebra pattern – ZP), considering that ZPs are generated in loops having an exponential density profile in their cross section. We took into account that when in a plasma there is a source emitting in all directions, then in the escape process from the plasma the emission has a directional character nearly perpendicular to the constant-density profile. Owing to the high directivity of the plasma emission (for emission at frequencies close to the plasma frequency), the region from which the emission escapes can be very small. We estimated the brightness temperature of three observed ZPs for two values of the density scale height (1 and 0.21 Mm) and two values of the loop width (1 and 2 arcsec). In all cases, high brightness temperatures were obtained. For the higher value of the density scale height, the brightness temperature was estimated to be \(1.1 \times 10^{15}\) – \(1.3 \times 10^{17}~\mbox{K}\), and for the lower value, it was \(4.7 \times 10^{13}\) – \(5.6\times 10^{15}~\mbox{K}\). These temperatures show that the observational probability of a burst with a ZP, which is generated in the transition region with a steep gradient of the plasma density, is significantly higher than for a burst generated in a region with smoother changes of the plasma density. We also computed the saturation energy density of the upper-hybrid waves (according to the double plasma resonance model, they are generated in the Zebra source) using a 3D particle-in-cell model with a loss-cone type of distribution of hot electrons. We found that this saturated energy is proportional to the ratio of hot electron and background plasma densities. Thus, comparing the growth rate and collisional damping of the upper-hybrid waves, we estimated minimum densities of hot electrons as well as the minimum value of the saturation energy density of the upper-hybrid waves. Finally, we compared the computed energy density of the upper-hybrid waves with the energy density of the electromagnetic waves in the Zebra source and thus estimated the efficiency of the wave transformation.
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brightness temperature of radio Zebras and wave energy densities in their sources
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: L V Yasnov, Jan Benacek, M KarlickýAbstract:We estimated the brightness temperature of radio Zebras (Zebra pattern -- ZP), considering that ZPs are generated in loops having an exponential density profile in their cross-section. We took into account that when in plasma there is a source emitting in all directions, then in the escape process from the plasma the emission obtains a directional character nearly perpendicular to the constant-density profile. Owing to the high directivity of the plasma emission the region from which the emission escapes can be very small. We estimated the brightness temperature of three observed ZPs for two values of the density scale height (1 and 0.21 Mm) and two values of the loop width (1 and 2 arcsec). In all cases high brightness temperatures were obtained. For the higher value of the density scale height, the brightness temperature was estimated as 1.1 $\times$ 10$^{15}$ - 1.3 $\times$ 10$^{17}$ K, and for the lower value as 4.7 $\times$ 10$^{13}$ - 5.6 $\times$ 10$^{15}$ K. We also computed the saturation energy density of the upper-hybrid waves (which according to the double plasma resonance model are generated in the Zebra source) using a 3D particle-in-cell model with the loss-cone type of distribution of hot electrons. We found that this saturated energy is proportional to the ratio of hot electron and background plasma densities. Thus, comparing the growth rate and collisional damping of the upper-hybrid waves, we estimated minimal densities of hot electrons as well as the minimal value of the saturation energy density of the upper-hybrid waves. Finally, we compared the computed energy density of the upper-hybrid waves with the energy density of the electromagnetic waves in the Zebra source and thus estimated the efficiency of the wave transformation.
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spike like bursts as fine structure of Zebras
Solar Physics, 2007Co-Authors: P Zlobec, M KarlickýAbstract:We studied the characteristics of the Zebra-associated spike-like bursts that were recorded with high time resolution at 1420 MHz in four intervals (from 12:45 to 12:48 UT) during 5 August 2003. Our detailed analysis is based on the selection of more than 500 such spike-like bursts and it is, at least to our knowledge, the first study devoted to such short-lived bursts. Their characteristics are different from those pertinent to “normal” spike bursts, as presented in the paper by Gudel and Benz (Astron. Astrophys. 231, 202, 1990); in particular, their duration (about 7.4 ms at half power) is shorter, so they should be members of the SSS (super short structures) family (Magdalenic et al., Astrophys. J. 642, L77, 2006). The bursts were generally strongly R-polarized; however, during the decaying part of interval I a low R-polarized and L-polarized bursts were also present. This change of polarization shows a trend that resembles the peculiar form of the Zebra lines in the spectral dominion (“V” like). A global statistical analysis on the bursts observed in the two polarimetric channels shows that the highest cross-correlation coefficient (about 0.5) was pertinent to interval I. The Zebras and the bursts can be interpreted by the same double plasma resonance process as proposed by Barta and Karlický (Astron. Astrophys. 379, 1045, 2001) and Karlický et al. (Astron. Astrophys. 375, 638, 2001); in particular, the spikes are generated by the interruption of this process by assumed turbulence (density or magnetic field variations). This process should be present in the region close to the reconnection site (e.g., in the plasma reconnection outflows) where the density and the magnetic field vary strongly.
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observation of harmonically related solar radio Zebra patterns in the 1 4 ghz frequency range
Astronomy and Astrophysics, 2002Co-Authors: H S Sawant, M Karlický, F C R Fernandes, J R CecattoAbstract:A unique case of two Zebra patterns related harmonically with ratio of1:2 was observed by distant radio telescopes at Sao Jose dos Campos and Ondrejov Observatories. Accompanied Zebras show that the ratio of frequencies of the neighboring Zebra lines is in the range of 1.009-1.037. There is a tendency of a decrease of this ratio with decreasing frequency within the specific Zebra pattern. Both facts speak in favour of plasma emission models for the Zebra pattern fine structure in radio burst continua.
Edward L Mills - One of the best experts on this subject based on the ideXlab platform.
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response of yellow perch perca flavescens in oneida lake new york to the establishment of Zebra mussels dreissena polymorpha
Canadian Journal of Fisheries and Aquatic Sciences, 2000Co-Authors: Christine M Mayer, Lars G Rudstam, Anthony J Vandevalk, John L Forney, Edward L MillsAbstract:We used long-term data on Oneida Lake, New York, to evaluate hypotheses about the effects of introduced Zebra mussels (Dreissena polymorpha) on yellow perch (Perca flavescens). We detected no change in survival, diet, or numbers of young-of-the-year (YOY) yellow perch. YOY growth increased in association with Zebra mussel introduc- tion and was marginally correlated with zooplankton size, which increased after Zebra mussel introduction. Low num- bers of YOY in recent years did not explain their increased growth rate. The percentage of age 3 and older yellow perch that consumed zooplankton and benthos increased after Zebra mussel introduction. Water clarity, which has increased since Zebra mussel introduction, was inversely related to the percentage of the adult population with empty stomachs and positively related to the percentage that consumed benthos. The percentage of adult yellow perch that consumed zooplankton was positively related to zooplankton size. Despite the increase in percentage of adults consum- ing both types of invertebrate prey, we detected no changes in adult growth associated with Zebra mussel introduction. This suggests that the principal effects of Zebra mussels on yellow perch in Oneida Lake were not via benthic path- ways but through modifications of water clarity and zooplankton. Thus far, these effects have not been negative for the yellow perch population.
