1,034 research outputs found
The Dipole Observed in the COBE DMR Four-Year Data
The largest anisotropy in the cosmic microwave background (CMB) is the
mK dipole assumed to be due to our velocity with respect to the
CMB. Using the four year data set from all six channels of the COBE
Differential Microwave Radiometers (DMR), we obtain a best-fit dipole amplitude
mK in the direction , where the first
uncertainties are statistical and the second include calibration and combined
systematic uncertainties. This measurement is consistent with previous DMR and
FIRAS resultsComment: New and improved version; to be published in ApJ next mont
Characterization of the protein import apparatus in isolated outer envelopes of chloroplasts
Isolated outer envelope membrane from pea (Pisum
sativum L.) chloroplasts can be used in vitro to study
binding and partial translocation of precursor proteins
destined for the inside of the organelle. Efficient binding
to a receptor protein on the outside of the membrane
vesicle and generation of a translocation intermediate
depends strictly on the presence of ATP. Protease
treatment of the translocation intermediate demonstrates
its insertion into the membrane. The membraneinserted
precursor protein cannot be extracted by 1 M
NaCl and is also NaOH resistant to a large extent. Mild
solubilization of outer envelope membranes by detergent
resulted in the isolation of a complex which still
contained the precursor protein. We have identified a
constitutively expressed homologue hsc 70 as part of
this membrane complex. Antibodies against hsp 70
(inducible heat shock protein 70) were able to immunoprecipitate
the complex bound precursor protein.
A second protein of 86 kDa molecular weight (OEP 86)
from the outer envelope membrane was also identified
as a major component of this complex
Translocation of proteins into isolated chloroplasts requires cytosolic factors to obtain import competence
The precursor form of the major-harvesting chlorophyll a/b-binding protein (pLHCP) of chloroplast thylakoids was overproduced in E. coli cells and used to study the influence of soluble factors on post-translational protein import into isolated pea chloroplasts. pLHCP solubilised in 8 M urea was not import-competent. However, if pLHCP was dialysed in the presence of soluble proteins (leaf extract) after urea treatment, import competence was gained. Dialysis of pLHCP in the presence of leaf extract alters its protease sensitivity. Stremai proteins, ovalbumin, trypsin inhibitor or chloroplast lipids could not produce import competence of pLHCP. Two components from leaf extract seem to be necessary, one of which can be mimicked by purified hsc 70, the other one requiring ATP. We conclude that soluble proteins from outside the stromal compartment are necessary for post-translational import of proteins into chloroplasts
Transfer of a chloroplast-bound precursor protein into the translocation apparatus is impaired after phospholipase C treatment
We have studied the influence of phospholipase C treatment of intact purified chloroplast on the translocation of a plastid destined precursor protein. Under standard import conditions, i.e. in the light in the presence or 2 mM ATP translocation was completely abolished but binding was observed at slightly elevated levels. An experimental regime which allowed binding but not import of the precursor protein, i.e. in the dark in the presence of 10 ÎŒM ATP, demonstrated that translocation intermediates, normally detected at this stage, were missing in phospholipase treated chloroplasts. The precursor was completely sensitive to protease treatment, indicating that the transfer of the precursor from the receptor to the import apparatus was blocked by phospholipase treatment
Phylogenetic profiling of the Arabidopsis thaliana proteome: what proteins distinguish plants from other organisms?
BACKGROUND: The availability of the complete genome sequence of Arabidopsis thaliana together with those of other organisms provides an opportunity to decipher the genetic factors that define plant form and function. To begin this task, we have classified the nuclear protein-coding genes of Arabidopsis thaliana on the basis of their pattern of sequence similarity to organisms across the three domains of life. RESULTS: We identified 3,848 Arabidopsis proteins that are likely to be found solely within the plant lineage. More than half of these plant-specific proteins are of unknown function, emphasizing the general lack of knowledge of processes unique to plants. Plant-specific proteins that are membrane-associated and/or targeted to the mitochondria or chloroplasts are the most poorly characterized. Analyses of microarray data indicate that genes coding for plant-specific proteins, but not evolutionarily conserved proteins, are more likely to be expressed in an organ-specific manner. A large proportion (13%) of plant-specific proteins are transcription factors, whereas other basic cellular processes are under-represented, suggesting that evolution of plant-specific control of gene expression contributed to making plants different from other eukaryotes. CONCLUSIONS: We identified and characterized the Arabidopsis proteins that are most likely to be plant-specific. Our results provide a genome-wide assessment that supports the hypothesis that evolution of higher plant complexity and diversity is related to the evolution of regulatory mechanisms. Because proteins that are unique to the green plant lineage will not be studied in other model systems, they should be attractive priorities for future studies
Le Passavant de Théodore de BÚze
Ă mi-chemin entre lâĂloge de la Folie dâĂrasme (1511) et le Tableau des diffĂ©rends de la Religion de Marnix de Sainte-Aldegonde (1599), ThĂ©odore de BĂšze fait publier lâEpistola Magistri Benedicti Passavantii (le Passavant) qui, comme eux, sâattaque aux abus de lâĂglise romaine. LâĂ©pĂźtre satirique, Ă©crite dans un latin macaronique Ă©tincelant, est adressĂ©e Ă Pierre Lizet, ancien prĂ©sident du parlement de Paris et, Ă lâĂ©poque, abbĂ© commendataire de lâabbaye parisienne de Saint-Victor. Tout comme..
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