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L Nover

Publications and source records attributed to L Nover.

At least 37 records · Page 2Linked to original sources
PubMed1990

Three tomato genes code for heat stress transcription factors with a region of remarkable homology to the DNA-binding domain of the yeast HSF.

Heat stress (hs) treatment of cell cultures of Lycopersicon peruvianum (Lp, tomato) results in activation of preformed transcription factor(s) (HSF) binding to the heat stress consensus element (HSE). Using appropriate synthetic HSE oligonucleotides, three types of clones with potential HSE binding domains were isolated from a tomato lambda gt11 expression library by DNA-ligand screening. One of the potential HSF genes is constitutively expressed, the other two are hs-induced. Sequence comparison defines a single domain of approximately 90 amino acid residues common to all three genes and to the HSE--binding domain of the yeast HSF. The domain is flanked by proline residues and characterized by two long overlapping repeats. We speculate that the derived consensus sequence is also representative for other eukaryotic HSF and that the existence of several different HSF is not unique to plants.

Amino Acid Sequence↗
PubMed1990

[Molecular cell biology of the heat stress response. II].

The coordinate induction of distinct genes by heat stress and a considerable number of chemical stressors depend on a common regulatory element in the promoter found in front of related genes of all eukaryotic systems. This element can be used for the construction of universal heat stress expression cassettes. The increasingly broad interest in the heat stress response and the genes involved also results from medical aspects, e.g., the potential application of hyperthermia in cancer therapy, the intricate connections of stress proteins and genes with malignant transformation, and the remarkable role of heat stress proteins as dominant antigens of infectious and autoimmune diseases.

Animals↗
PubMed1990

[Molecular cell biology of the heat stress response. Part I].

In a physiological range of hyperthermia all living systems respond with a complex reprogramming of cellular activities to provide a basis for survival during the stress period and for a rapid restoration of normal activities in the recovery period. A prominent characteristic of the response is the induced synthesis of heat-stress proteins which is likewise evoked by numerous chemical stressors. The common signal transduction chain leading to the activation of heat-stress genes evidently involves the transient accumulation of abnormal proteins. The dominant HSPs belong to five conserved stress protein families, whose members are essential components of all living cells with general functions by far exceeding the stress response.

Animals↗
PubMed1989

Cytoplasmic heat shock granules are formed from precursor particles and are associated with a specific set of mRNAs.

In heat-shocked tomato cell cultures, cytoplasmic heat shock granules (HSGs) are tightly associated with a specific subset of mRNAs coding mainly for the untranslated control proteins. This messenger ribonucleoprotein complex was banded in a CsCl gradient after fixation with formaldehyde (approximately 1.30 g/cm3). It contains all the heat shock proteins and most of the RNA applied to the gradient. During heat shock, a reversible aggregation of HSGs from 15S precursor particles can be shown. These pre-HSGs are not identical to the 19S plant prosomes. Ultrastructural analysis supports the ribonucleoprotein nature of HSGs and their composition of approximately 10-nm precursor particles. A model summarizes our results. It gives a reasonable explanation for the striking conservation of untranslated mRNAs during heat shock and may apply also to animal cells.

Cytoplasmic Granules↗
PubMed1989

125 years of experimental heat shock research: historical roots of a discipline.

The history of experimental heat shock research over the last 125 years is briefly, outlined. Starting with reports on the upper temperature limits of plant survival (1864) and on the spontaneous regression of skin cancer after a severe local inflammation (1866), studies on the heat shock response today are a major field of modern cell biology and include all types of prokaryotic and eukaryotic organisms.

Animals↗
PubMed1986

Control of ribosome biosynthesis in plant cell cultures under heat-shock conditions. Ribosomal RNA.

The immediate block of ribosome biosynthesis in heat-shocked tomato cell cultures is primarily caused by the complete inhibition of pre-rRNP processing. Depending on the heat-shock conditions synthesis of pre-rRNP goes on, though at a reduced level. Synthesis and/or preservation of pre-rRNP during heat shock as well as its efficient processing in the recovery period are thoroughly improved by preconditioning of cells to the hyperthermic treatment. Such preinduced cultures are characterized by their content of preformed heat-shock proteins, whose dominant representative (hsp 70) becomes highly enriched in the characteristic granular rRNP material observed in nucleoli of heat-shocked cells. This is shown by immune fluorescence staining and microautoradiography.

Autoradiography↗
PubMed1984

Synthesis, modification and structural binding of heat-shock proteins in tomato cell cultures.

Synthesis of about 30 acidic and 18 basic heat-shock proteins (hsps) is induced in suspension cultures of tomato (Lycopersicon peruvianum) if subjected to supraoptimal temperature conditions (35-40 degrees C). A characteristic aspect of the plant heat-shock response is the formation of cytoplasmic granular aggregates, heat-shock granules, containing distinct heat-shock proteins as major structural components and, in addition, several hitherto undetected minor acidic and basic heat-shock proteins. Structural binding of heat-shock proteins, i.e. assembly of heat-shock granules, is dependent on the persistance of supraoptimal temperature conditions. Despite the ongoing synthesis also at 25 degrees C, e.g. in pulse heat-shocked cultures, these proteins are accumulated exclusively in soluble form. Individual heat-shock proteins are characterized by their kinetics of synthesis and are classified by their compartmentation behaviour into class A proteins (exclusively found in soluble form, e.g. hsps 95 and 80), class B proteins (5-10% bound to heat-shock granules, e.g. hsps 70, 68), class C proteins (30-80% bound to heat-shock granules, e.g. hsps 21, 17, 15) and class D proteins, which are minor heat-shock proteins only detected in structure-bound form. Major representatives are modified proteins, i.e. hsps 95, 80, 70 and 68 are phosphorylated and hsps 80, 74, 70 and 17 are methylated proteins (numbers 70, 80 etc. refer to 10(-3) Mr). Under heat-shock conditions synthesis of the proteins detected in control cells (25 degrees C proteins) exhibits two patterns. There are proteins with continued and proteins with discontinued synthesis. Synthesis of most of the latter proteins is resumed very rapidly after shift-down to 25 degrees C, even in the presence of actinomycin D. We conclude that reversible segregation of distinct mRNA species from the translation apparatus contributes to the heat-shock-specific pattern of protein synthesis in plants also.

Autoradiography↗
PubMed1984

Heat shock induced changes of plant cell ultrastructure and autoradiographic localization of heat shock proteins.

Treating tomato cell cultures and leaves by a physiological heat shock (hs) at 35 to 39 degrees C results in a progressive disintegration of the nucleolus and the assembly of cytoplasmic hs granules. Other ultrastructural changes are not observed. The alterations of the nucleoli coincide with an immediate stop of the processing and with a strongly decreased synthesis of pre-rRNA. Both hs effects are reversed after shift-down to normal temperature conditions (25 degrees C). Assembly of cytoplasmic hs granules depends on the accumulation of the newly forming hs proteins and on supraoptimal temperatures. It is not observed in preinduced cultures synthesizing hs proteins at 25 degrees C. Autoradiographic studies reveal the preferential accumulation of hsp in the nucleoli and hs granules. Furthermore uridine labeling points to the presence of RNA in electron dense particles of both subcellular components. A survey on the state of hsp synthesis and structural binding as well as on the ultrastructural changes is given for 12 selected hs regimes.

Autoradiography↗
PubMed1983

Formation of cytoplasmic heat shock granules in tomato cell cultures and leaves.

Biochemical and electron microscopic analyses of heat-shocked suspension cultures of Peruvian tomato (Lycopersicon peruvianum) revealed that a considerable part of the dominant small heat shock proteins (hsps) with an Mr of approximately 17,000 are structural proteins of newly forming granular aggregates in the cytoplasm (heat shock granules), whose formation strictly depends on heat shock conditions (37 to 40 degrees C) and the presence or simultaneous synthesis of hsps. However, under certain conditions, e.g., in preinduced cultures maintained at 25 degrees C, hsps also accumulate as soluble proteins without concomitant assembly of heat shock granules. Similar heat shock-induced cytoplasmic aggregates were also observed in other cell cultures and heat-shocked tomato leaves and corn coleoptiles.

Cytoplasmic Granules↗
PubMed1982

Heat-shock-induced alterations of ribosomal protein phosphorylation in plant cell cultures.

Heat shock of cell suspension cultures of tomato (Lycopersicon peruvianum) results in a rapid and reversible decline of the phosphorylation level of a single basic ribosomal protein of the small subunit (tentatively identified as ribosomal protein S6). Simultaneously, phosphate labeling of several acidic ribosomal proteins of the large subunit is enhanced. Data on the temperature-dependent distribution of S6 subspecies and on the kinetics and reversibility of S6 phosphorylation are given. The decreased phosphorylation of S6 at temperatures higher than 35 degrees C coincides with the onset of heat shock protein synthesis and precedes a decline of the mitotic index. Recovery from heat shock is characterized by S6 rephosphorylation and, subsequently, leads to an abnormally high mitotic index.

Cell Division↗
PubMed1979

Channelling of exogenous phenylalanine to the sites of storage and the sites of alkaloid and protein biosynthesis in Penicillium cyclopium.

Externally applied L-phenylalanine rapidly equilibrates with the cytosolic pool(s) in hyphae of emerged cultures of Penicillium cyclopium. If not incorporated into protein it is accumulated in the so called expandable pool, which is presumably localized in the vacuolar compartment. At high concentrations of exogenous L-phenylalanine practically all of the amino acid needed for protein synthesis comes from the extracellular source, contrary to alkaloid synthesis which under all conditions recruits more than 90% of the required L-phenylalanine from intracellular sources. Two pathways of alkaloid labelling can be distinguished, by which externally applied L-phenylalanine reaches the sites of alkaloid synthesis: (1) a direct way from cytosolic pool (primary labelling) and (2) an indirect way via the expandable pool (secondary labelling).

Alkaloids↗
PubMed1978

[Selection and characterization of Penicillium cyclopium mutants with altered developmental program].

After treatment with NNMG, NaNO2 or UV-light of conidiospores of Penicillium cyclopium strain SM 72 variant strains (mutants) with altered developmental programme were selected. Additionally from a methionine-auxotrophic mutant of P. cyclopium prototrophic revertants were prepared. Investigation of the alkaloid metabolism and other idiophase processes has shown that these mutant strains can be divided into two groups (cf. table 1): a) Mutants with a depression of all idiophase features. The defects of these strains presumably affect central regulatory processes which, as in strain rev-met 83a, can be reversed spontaneously by an one-step mechanism and b) mutants defective in certain parts of the idiophase programme only, demonstrating that there is a certain autonomy in regulation of the individual parts of the programme.

Alkaloids↗