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  • 1
    Electronic Resource
    Electronic Resource
    Intracellular transport and processing of a tobacco vacuolar β-1,3-glucanase (1992)
    Springer
    Planta 188 (1992), S. 559-565 
    Details
    ISSN: 1432-2048
    Keywords: Chitinase ; C-terminal processing ; β-1,3-glucanase ; Glycosylation ; Nicotiana ; Pathogenesis-related proteins ; Vacuole (targeting)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The class I β-1,3-glucanases are basic, vacuolar enzymes implicated in the defense of plants against pathogen infection. The tobacco (Nicotiana tabacum L.) enzyme is synthesized as a preproprotein with an N-terminal signal peptide for targeting to the lumen of the endoplasmic reticulum and an N-glycosylated C-terminal extension which is lost during protein maturation. The transport and processing of β-1,3-glucanase in cellsuspension cultures of the tobacco cultivar Havana 425 was investigated by pulse-chase labelling and cell fractionation. We verified that mature β-1,3-glucanase is localized in the vacuole of the suspension-cultured cells. Comparison of the time course of processing in homogenates, the soluble fraction, and membrane fractions indicates that proglucanase is transported from the endoplasmic reticulum via the Golgi compartment to the vacuole. Processing to the mature form occurs in the vacuole. Treatment of cells with tunicamycin, which inhibits N-glycosylation, and digestion of the 35S-labelled processing intermediates with endoglycosidase H indicate that β-1,3-glucanase has a single N-glycan attached to the C-terminal extension. Glycosylation is not required for proteolytic processing or correct targeting to the vacuole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197049
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics of prolyl hydroxylation, intracellular transport and C-terminal processing of the tobacco vacuolar chitinase (1995)
    Springer
    Planta 197 (1995), S. 250-256 
    Details
    ISSN: 1432-2048
    Keywords: Chitinase ; C-terminal processing ; Gene-expression (transient) ; Intracellular transport ; Nicotiana ; Vacuole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dynamics of intracellular transport and processing of one of the vacuolar chitinases of tobacco (Nic-otiana tabacum L.), chitinase A (CHN A; EC 3.2.1.14), was investigated with pulse-chase experiments in conjunction with cell fractionation and immunoprecipitation. Mature CHN A is composed of two domains, the N-terminal cysteine-rich chitin-binding domain and the catalytic domain, linked by a short peptide spacer containing several hydroxyprolines. It is synthetized as a preproprotein with a signal peptide for cotranslational transport into the endoplasmic reticulum (ER) and a C-terminal, vacuolar targeting peptide (VTP) required for targeting to the vacuole, which is removed by proteolytic cleavage. We investigated transformed N. sylvestris plants constitutively expressing CHN A or a mutant CHN A lacking the chitin-binding domain and spacer (ΔCS CHN A), as well as N. plumbaginifolia protoplasts transiently expressing the same constructs. Processing and transport in the two systems was very similar. A shift in the apparent molecular weight of chitinase, indicative of prolyl hydroxylation, was detectable only 30 min after appearance of newly synthesized prochitinase, indicating that it might occur in a post-ER compartment. In total, labelled chitinase was detected in the microsomal fraction for up to 90–120 min as a prochitinase, bearing the VTP. Later, it appeared only in the soluble fraction (comprising the vacuolar sap) as the mature CHN A without the VTP. In both systems, intracellular transport and processing of ΔCS CHN A was faster than that of the wildtype form, indicating that correct folding of the cysteine-rich chitin-binding domain and/or prolyl hydroxylation of the spacer delays transport to the vacuole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202644
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  • 3
    Electronic Resource
    Electronic Resource
    Regulated inactivation of homologous gene expression in transgenic Nicotiana sylvestris plants containing a defense-related tobacco chitinase gene (1992)
    Springer
    Molecular genetics and genomics 235 (1992), S. 179-188 
    Details
    ISSN: 1617-4623
    Keywords: Plant-defense ; Gene-silencing ; Co-suppression ; Chitinase ; DNA-methylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The class I chitinases are vacuolar proteins implicated in the defense of plants against pathogens. Leaves of transgenic Nicotiana sylvestris plants homozygous for a chimeric tobacco (Nicotiana tabacum) chitinase gene with Cauliflower Mosaic Virus (CaMV) 35S RNA expression signals usually accumulate high levels of chitinase relative to comparable leaves of non-transformed plants. Unexpectedly, some transgenic plants accumulated lower levels of chitinase than nontransformed plants. We call this phenomenon silencing. The incidence of silencing depends on the early rearing conditions of the plants. When grown to maturity in a greenhouse, ≈25% of plants raised as seedlings in closed culture vessels were of the silent type; none of the plants raised from seed in a greenhouse showed this phenotype. Silencing is also developmentally regulated. Plants showed three patterns of chitinase expression: uniformly high levels of expression in different leaves, uniformly low levels of expression in different leaves, and position-dependent silencing in which expression was uniform within individual leaves but varied in different leaves on the same plant. Heritability of the silent phenotype was examined in plants homozygous for the transgene. Some direct descendants exhibited a high-silent-high sequence of activity phenotypes in successive sexual generations, which cannot be explained by simple Mendelian inheritance. Taken together, the results indicate that silencing results from stable but potentially reversible states of gene expression that are not meiotically transmitted. Gene-specific measurements of chitinase and chitinase mRNA showed that silencing results from co-suppression, i.e. the inactivation of both host and transgene expression in trans. The silent state was not correlated with cytosine methylation of the transgene at the five restriction sites investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279359
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