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  • American Society for Microbiology  (8)
  • 1
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2001
    In:  Journal of Virology Vol. 75, No. 15 ( 2001-08), p. 6769-6775
    In: Journal of Virology, American Society for Microbiology, Vol. 75, No. 15 ( 2001-08), p. 6769-6775
    Kurzfassung: The yeast retrotransposon Ty1 encodes a 7-nucleotide RNA sequence that directs a programmed, +1 ribosomal frameshifting event required for Gag-Pol translation and retrotransposition. We report mutations that block frameshifting, which can be suppressed in cis by “transplanting” the frameshift signal to a position upstream of its native location. These “frameshift transplant” mutants transpose with only a modest decrease in efficiency, suggesting that the location of the frameshift signal in a functional Ty1 element may vary. The genomic architecture of Ty1 is such that Gag, Ty1 PR (PR), and the Gag-derived p4 peptide share a common sequence. The functional independence of the movement of the frameshift signal to a new location within the Ty1 element is used to unambiguously attribute the effect of mutations deleterious to transposition in this region of overlapping coding sequences to effects on the Ty1 (PR). This work defines the amino terminus of the Ty1 PR and introduces a new technique for studying viral genome organization.
    Materialart: Online-Ressource
    ISSN: 0022-538X , 1098-5514
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2001
    ZDB Id: 1495529-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2002
    In:  Journal of Virology Vol. 76, No. 1 ( 2002-01), p. 346-354
    In: Journal of Virology, American Society for Microbiology, Vol. 76, No. 1 ( 2002-01), p. 346-354
    Kurzfassung: Ty1 is the most successful of the five endogenous yeast retrotransposons. The life cycle of Ty1 dictates that a number of nucleocapsid (NC)-facilitated events occur although the protein(s) responsible for these events has not been identified. The positioning of the NC peptide is conserved at the carboxy terminus of the Gag protein among most long terminal repeat (LTR)-containing retroelements. An analogous region of Ty1 that simultaneously encodes part of Gag, protease (PR), and the C-terminal p4 peptide was mutagenized. Some of these mutations result in smaller-than-normal virus-like particles (VLPs). The mutants were also found to impair an NC-like functionality contained within the amino terminus of the protease that is distinct and separable from its proteolytic activity. Remarkably, these mutants have distinct defects in reverse transcription.
    Materialart: Online-Ressource
    ISSN: 0022-538X , 1098-5514
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2002
    ZDB Id: 1495529-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2004
    In:  Eukaryotic Cell Vol. 3, No. 5 ( 2004-10), p. 1287-1296
    In: Eukaryotic Cell, American Society for Microbiology, Vol. 3, No. 5 ( 2004-10), p. 1287-1296
    Kurzfassung: FKBP12 is a conserved member of the prolyl-isomerase enzyme family and serves as the intracellular receptor for FK506 that mediates immunosuppression in mammals and antimicrobial actions in fungi. To investigate the cellular functions of FKBP12 in Saccharomyces cerevisiae , we employed a high-throughput assay to identify mutations that are synthetically lethal with a mutation in the FPR1 gene, which encodes FKBP12. This screen identified a mutation in the HOM6 gene, which encodes homoserine dehydrogenase, the enzyme catalyzing the last step in conversion of aspartic acid into homoserine, the common precursor in threonine and methionine synthesis. Lethality of fpr1 hom6 double mutants was suppressed by null mutations in HOM3 or HOM2 , encoding aspartokinase and aspartate β-semialdehyde dehydrogenase, respectively, supporting the hypothesis that fpr1 hom6 double mutants are inviable because of toxic accumulation of aspartate β-semialdehyde, the substrate of homoserine dehydrogenase. Our findings also indicate that mutation or inhibition of FKBP12 dysregulates the homoserine synthetic pathway by perturbing aspartokinase feedback inhibition by threonine. Because this pathway is conserved in fungi but not in mammals, our findings suggest a facile route to synergistic antifungal drug development via concomitant inhibition of FKBP12 and Hom6.
    Materialart: Online-Ressource
    ISSN: 1535-9778 , 1535-9786
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2004
    ZDB Id: 2071564-X
    SSG: 12
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2002
    In:  Journal of Virology Vol. 76, No. 9 ( 2002-05), p. 4233-4240
    In: Journal of Virology, American Society for Microbiology, Vol. 76, No. 9 ( 2002-05), p. 4233-4240
    Kurzfassung: Retrotransposition of the Ty1 element of Saccharomyces cerevisiae is temperature sensitive. Transposition activity of Ty1 is abolished at temperatures above 34°C. In this report, we show that the major block to transposition at high temperature is the inhibition of processing of the Gag-Pol-p199 polyprotein and the concomitant reduction of reverse transcriptase (RT) activity. Expression of a Ty1 protease construct in Escherichia coli shows that protease enzymatic activity is inherently temperature sensitive. In yeast, Gag processing is only partially inhibited at high temperature, while cleavage of the Gag-Pol polyprotein is completely inhibited. Sites of proteolytic processing are differentially susceptible to cleavage during growth at high temperature. Overall levels of the Gag-Pol polyprotein are reduced at high temperature, although the efficiency of the requisite +1 frameshifting event appears to be increased. RT activity is inherently relatively temperature resistant, yet no cDNA is made at high temperature and the amount of RT activity is greatly reduced in virus-like particles formed at high temperature. Taken together, these results suggest that alterations in Ty1 proteins that occur at high temperature affect both protease activity and RT activity, such that Ty1 transposition is abolished.
    Materialart: Online-Ressource
    ISSN: 0022-538X , 1098-5514
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2002
    ZDB Id: 1495529-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2001
    In:  Journal of Virology Vol. 75, No. 2 ( 2001-01-15), p. 638-644
    In: Journal of Virology, American Society for Microbiology, Vol. 75, No. 2 ( 2001-01-15), p. 638-644
    Kurzfassung: The retroviral protease is a key enzyme in a viral multienzyme complex that initiates an ordered sequence of events leading to virus assembly and propagation. Viral peptides are initially synthesized as polyprotein precursors; these precursors undergo a number of proteolytic cleavages executed by the protease in a specific and presumably ordered manner. To determine the role of individual protease cleavage sites in Ty1, a retrotransposon from Saccharomyces cerevisiae , the cleavage sites were systematically mutagenized. Altering the cleavage sites of the yeast Ty1 retrotransposon produces mutants with distinct retrotransposition phenotypes. Blocking the Gag/PR site also blocks cleavage at the other two cleavage sites, PR/IN and IN/RT. In contrast, mutational block of the PR/IN or IN/RT sites does not prevent cleavage at the other two sites. Retrotransposons with mutations in each of these sites have transposition defects. Mutations in the PR/IN and IN/RT sites, but not in the Gag/PR site, can be complemented in trans by endogenous Ty1 copies. Hence, the digestion of the Gag/PR site and release of the protease N terminus is a prerequisite for processing at the remaining sites; cleavage of PR/IN is not required for the cleavage of IN/RT, and vice versa. Of the three cleavage sites in the Gag-Pol precursor, the Gag/PR site is processed first. Thus, Ty1 Gag-Pol processing proceeds by an ordered pathway.
    Materialart: Online-Ressource
    ISSN: 0022-538X , 1098-5514
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2001
    ZDB Id: 1495529-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2007
    In:  Journal of Virology Vol. 81, No. 17 ( 2007-09), p. 9004-9012
    In: Journal of Virology, American Society for Microbiology, Vol. 81, No. 17 ( 2007-09), p. 9004-9012
    Kurzfassung: Ty1 reverse transcriptase/RNase H (RT/RH) is exquisitely sensitive to manganese concentrations. Elevated intracellular free Mn 2+ inhibits Ty1 retrotransposition and in vitro Ty1 RT-polymerizing activity. Furthermore, Mn 2+ inhibition is not limited to the Ty1 RT, as this ion similarly inhibits the activities of both avian myeloblastosis virus and human immunodeficiency virus type 1 RTs. To further characterize Mn 2+ inhibition, we generated RT/RH suppressor mutants capable of increased Ty1 transposition in pmr1 Δ cells. PMR1 codes for a P-type ATPase that regulates intracellular calcium and manganese ion homeostasis, and pmr1 mutants accumulate elevated intracellular manganese levels and display 100-fold less transposition than PMR1 + cells. Mapping of these suppressor mutations revealed, surprisingly, that suppressor point mutations localize not to the RT itself but to the RH domain of the protein. Furthermore, Mn 2+ inhibition of in vitro RT activity is greatly reduced in all the suppressor mutants, whereas RH activity and cleavage specificity remain largely unchanged. These intriguing results reveal that the effect of these suppressor mutations is transmitted to the polymerase domain and suggest biochemical communication between these two domains during reverse transcription.
    Materialart: Online-Ressource
    ISSN: 0022-538X , 1098-5514
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2007
    ZDB Id: 1495529-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2001
    In:  Journal of Virology Vol. 75, No. 15 ( 2001-08), p. 7030-7041
    In: Journal of Virology, American Society for Microbiology, Vol. 75, No. 15 ( 2001-08), p. 7030-7041
    Kurzfassung: Recently, remarkable progress has been made in developing effective combination drug therapies that can control but not cure retroviral replication. Even when effective, these drug regimens are toxic, they require demanding administration schedules, and resistant viruses can emerge. Thus the need for new gene-based therapies continues. In one such approach, capsid-targeted viral inactivation (CTVI), nucleases fused to viral coat proteins are expressed in infected cells and become incorporated during virion assembly. CTVI can eliminate infectious murine retrovirus titer in tissue culture. Here we describe transgenic mice expressing fusions of the Moloney murine leukemia virus (Mo-MuLV) Gag protein to staphylococcal nuclease. This work tests the protective effect and demonstrates in vivo proof-of-principle of CTVI in transgenic mice expressing endogenous proviral copies of Mo-MuLV. The antiviral protein-expressing mice are phenotypically normal, attesting to the lack of toxicity of the fusion protein. The Mo-MuLV infection was much less virulent in transgenic littermates than in nontransgenic littermates. Gag-nuclease expression reduced infectious titers in blood up to 10-fold, decreased splenomegaly and leukemic infiltration, and increased life spans up to 2.5-fold in transgenic relative to nontransgenic infected animals. These results suggest that gene therapies based on similar fusion proteins, designed to attack human immunodeficiency virus or other retroviruses, could provide substantial therapeutic benefits.
    Materialart: Online-Ressource
    ISSN: 0022-538X , 1098-5514
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2001
    ZDB Id: 1495529-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    Online-Ressource
    Online-Ressource
    American Society for Microbiology ; 2000
    In:  Journal of Virology Vol. 74, No. 24 ( 2000-12-15), p. 11811-11824
    In: Journal of Virology, American Society for Microbiology, Vol. 74, No. 24 ( 2000-12-15), p. 11811-11824
    Kurzfassung: Active nuclear import of the human immunodeficiency virus type 1 (HIV-1) preintegration complex (PIC) is essential for the productive infection of nondividing cells. Nuclear import of the PIC is mediated by the HIV-1 matrix protein, which also plays several critical roles during viral entry and possibly during virion production facilitating the export of Pr55 Gag and genomic RNA. Using a yeast two-hybrid screen, we identified a novel human virion-associated matrix-interacting protein (VAN) that is highly conserved in vertebrates and expressed in most human tissues. Its expression is upregulated upon activation of CD4 + T cells. VAN is efficiently incorporated into HIV-1 virions and, like matrix, shuttles between the nucleus and cytoplasm. Furthermore, overexpression of VAN significantly inhibits HIV-1 replication in tissue culture. We propose that VAN regulates matrix nuclear localization and, by extension, both nuclear import of the PIC and export of Pr55 Gag and viral genomic RNA during virion production. Our data suggest that this regulatory mechanism reflects a more global process for regulation of nucleocytoplasmic transport.
    Materialart: Online-Ressource
    ISSN: 0022-538X , 1098-5514
    Sprache: Englisch
    Verlag: American Society for Microbiology
    Publikationsdatum: 2000
    ZDB Id: 1495529-5
    Standort Signatur Einschränkungen Verfügbarkeit
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