Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Biogenesis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50Linked to original sources
PubMed2004

Mutations in ClpC2/Hsp100 suppress the requirement for FtsH in thylakoid membrane biogenesis.

The Arabidopsis var2 variegation mutant defines a nuclear gene for a chloroplast FtsH metalloprotease. Leaf variegation is expressed only in homozygous recessive plants. The cells in the green leaf sectors of this mutant contain morphologically normal chloroplasts, whereas cells in the white sectors contain abnormal plastids lacking organized lamellar structures. var2 mutants are hypersusceptible to photoinhibition, and VAR2 degrades unassembled polypeptides and is involved in the D1 repair cycle of photosystem II, likely by affecting turnover of the photodamaged D1 polypeptide. A second-site suppressor screen of var2 yielded a normal-appearing, nonvariegated line. Map-based cloning revealed that the suppression of variegation in this line is due to a splice site mutation in ClpC2, a chloroplast Hsp100 chaperone, that results in sharply reduced ClpC2 protein accumulation. Isolation of clpC2 single mutants showed that clpC2 is epistatic to var2, and that a lack of ClpC2 does not markedly alter the composition of the thylakoid membrane. Suppression by clpC2 is not allele-specific. Our results suggest that clpC2 is a suppressor of thylakoid biogenesis and maintenance and that ClpC2 might act by accelerating photooxidative stress. Arabidopsis has two ClpC genes (ClpC1 and ClpC2), and mutants with down-regulated expression of both genes have a phenotype different from clpC2, suggesting that ClpC1 and ClpC2 act synergistically and/or that they are only partially redundant. The isolation of a clpC2 mutant represents an important advance in the generation of tools to understand Hsp100 function and insight into the mechanisms of protein quality control in plants.

ATP-Dependent Proteases↗
PubMed2005

Mechanism of phagolysosome biogenesis block by viable Mycobacterium tuberculosis.

Live Mycobacterium tuberculosis persists in macrophage phagosomes by interfering with phagolysosome biogenesis. Here, using four-dimensional microscopy and in vitro assays, we report the principal difference between phagosomes containing live and dead mycobacteria. Phosphatidylinositol 3-phosphate (PI3P), a membrane trafficking regulatory lipid essential for phagosomal acquisition of lysosomal constituents, is retained on phagosomes harboring dead mycobacteria but is continuously eliminated from phagosomes with live bacilli. We show that the exclusion of PI3P from live mycobacterial phagosomes can be only transiently reversed by Ca2+ fluxes, and that live M. tuberculosis secretes a lipid phosphatase, SapM, that hydrolyzes PI3P, inhibits phagosome-late endosome fusion in vitro, and contributes to inhibition of phagosomal maturation.

Animals↗
PubMed2006

Apicoplast fatty acid synthesis is essential for organelle biogenesis and parasite survival in Toxoplasma gondii.

Apicomplexan parasites are the cause of numerous important human diseases including malaria and AIDS-associated opportunistic infections. Drug treatment for these diseases is not satisfactory and is threatened by resistance. The discovery of the apicoplast, a chloroplast-like organelle, presents drug targets unique to these parasites. The apicoplast-localized fatty acid synthesis (FAS II) pathway, a metabolic process fundamentally divergent from the analogous FAS I pathway in humans, represents one such target. However, the specific biological roles of apicoplast FAS II remain elusive. Furthermore, the parasite genome encodes additional and potentially redundant pathways for the synthesis of fatty acids. We have constructed a conditional null mutant of acyl carrier protein, a central component of the FAS II pathway in Toxoplasma gondii. Loss of FAS II severely compromises parasite growth in culture. We show FAS II to be required for the activation of pyruvate dehydrogenase, an important source of the metabolic precursor acetyl-CoA. Interestingly, acyl carrier protein knockout also leads to defects in apicoplast biogenesis and a consequent loss of the organelle. Most importantly, in vivo knockdown of apicoplast FAS II in a mouse model results in cure from a lethal challenge infection. In conclusion, our study demonstrates a direct link between apicoplast FAS II functions and parasite survival and pathogenesis. Our genetic model also offers a platform to dissect the integration of the apicoplast into parasite metabolism, especially its postulated interaction with the mitochondrion.

Acetates↗
PubMed2006

Biogenesis of actin-like bacterial cytoskeletal filaments destined for positioning prokaryotic magnetic organelles.

Magnetosomes comprise a magnetic nanocrystal surrounded by a lipid bilayer membrane. These unique prokaryotic organelles align inside magnetotactic bacterial cells and serve as an intracellular compass allowing the bacteria to navigate along the geomagnetic field in aquatic environments. Cryoelectron tomography of Magnetospirillum strains has revealed that the magnetosome chain is surrounded by a network of filaments that may be composed of MamK given that the filaments are absent in the mamK mutant cells. The process of the MamK filament assembly is unknown. Here we prove the authenticity of the MamK filaments and show that MamK exhibits linear distribution inside Magnetospirillum sp. cells even in the area without magnetosomes. The mamK gene alone is sufficient to direct the synthesis of straight filaments in Escherichia coli, and one extremity of the MamK filaments is located at the cellular pole. By using dual fluorescent labeling of MamK, we found that MamK nucleates at multiple sites and assembles into mosaic filaments. Time-lapse experiments reveal that the assembly of the MamK filaments is a highly dynamic and kinetically asymmetrical process. MamK bundles might initiate the formation of a new filament or associate to one preexistent filament. Our results demonstrate the mechanism of biogenesis of prokaryotic cytoskeletal filaments that are structurally and functionally distinct from the known MreB and ParM filaments. In addition to positioning magnetosomes, other hypothetical functions of the MamK filaments in magnetotaxis might include anchoring magnetosomes and being involved in magnetic reception.

Actins↗
PubMed2007

Chloroplast biogenesis: the use of mutants to study the etioplast-chloroplast transition.

In angiosperm plants, the etioplast-chloroplast transition is light-dependent. A key factor in this process is the protochlorophyllide oxidoreductase A (PORA), which catalyzes the light-induced reduction of protochlorophyllide to chlorophyllide. The import pathway of the precursor protein prePORA into chloroplasts was analyzed in vivo and in vitro by using homozygous loss-of-function mutants in genes coding for chlorophyllide a oxygenase (CAO) or for members of the outer-envelope solute-channel protein family of 16 kDa (OEP16), both of which have been implied to be key factors for the import of prePORA. Our in vivo analyses show that cao or oep16 mutants contain a normally structured prolamellar body that contains the protochlorophyllide holochrome. Furthermore, etioplasts from cao and oep16 mutants contain PORA protein as found by mass spectrometry. Our data demonstrate that both CAO and OEP16 are dispensable for chloroplast biogenesis and play no central role in the import of prePORA in vivo and in vitro as further indicated by protein import studies.

Arabidopsis↗
PubMed2000

Conversion of a c type cytochrome to a b type that spontaneously forms in vitro from apo protein and heme: implications for c type cytochrome biogenesis and folding.

Cytochrome c(552) from Hydrogenobacter thermophilus, a thermophilic bacterium, has been converted into a b type cytochrome, after mutagenesis of both heme-binding cysteines to alanine and expression in the cytoplasm of Escherichia coli. The b type variant is less stable, with the guanidine hydrochloride unfolding midpoint occurring at a concentration 2 M lower than for the wild-type protein. The reduction potential is 75 mV lower than that of the recombinant wild-type protein. The heme can be removed from the b type variant, thus generating an apo protein that has, according to circular dichroism spectroscopy, an alpha-helical content different from that of the holo b type protein. The latter is readily reformed in vitro by addition of heme to the apo protein. This reforming suggests that previously observed assembly of cytochrome c(552), which has the typical class I cytochrome c fold, in the E. coli cytoplasm is a consequence of spontaneous thioether bond formation after binding of heme to a prefolded polypeptide. These observations have implications for the general problem of c type cytochrome biogenesis.

Alanine↗
PubMed2002

The CcmE protein of the c-type cytochrome biogenesis system: unusual in vitro heme incorporation into apo-CcmE and transfer from holo-CcmE to apocytochrome.

Three key steps of cytochrome c biogenesis in many Gram-negative bacteria, the uptake of heme by the heme chaperone CcmE, the covalent attachment of heme to CcmE, and its subsequent release from CcmE to an apocytochrome c, have been achieved in vitro. apo-CcmE from Escherichia coli preferentially bound to ferric, with high affinity (K(d), 200 nM), rather than ferrous heme. The preference for ferric heme was confirmed by competition with 8-anilino-1-naphthalenesulfonate, which bound to a hydrophobic pocket in apo-CcmE. Reduction under certain conditions of the ferric heme-CcmE complex, which has characteristics of a b-type cytochrome, resulted in covalent attachment of heme to the protein. The resulting in vitro-produced holo-CcmE was identical to the in vivo-produced holo-CcmE, proving that unmodified Fe-protoporphyrin IX is incorporated into CcmE. Only noncovalent binding of mesoheme to CcmE was observed, thus implicating at least one vinyl group in covalent binding of heme to CcmE. Heme transferred in vitro from holo-CcmE to apocytochrome c, provided the heme was reduced. The necessity for reduced holo-CcmE might explain the role of the heme chaperone, i.e., prevention of reaction of ferric heme with apocytochrome and thus avoidance of incorrect side products. In addition, an AXXAH mutant of the CXXCH binding motif in the apocytochrome c was unable to accept heme from holo-CcmE. These in vitro results mimic, and thus have implications for, the molecular pathway of heme transfer during c-type cytochrome maturation in many species of bacteria in vivo.

Apoenzymes↗
PubMed2001

The initial steps of biogenesis of cyanobacterial photosystems occur in plasma membranes.

During oxygenic photosynthesis in cyanobacteria and chloroplasts of plants and eukaryotic algae, conversion of light energy to biologically useful chemical energy occurs in the specialized thylakoid membranes. Light-induced charge separation at the reaction centers of photosystems I and II, two multisubunit pigment-protein complexes in the thylakoid membranes, energetically drive sequential photosynthetic electron transfer reactions in this membrane system. In general, in the prokaryotic cyanobacterial cells, the thylakoid membrane is distinctly different from the plasma membrane. We have recently developed a two-dimensional separation procedure to purify thylakoid and plasma membranes from the genetically widely studied cyanobacterium Synechocystis sp. PCC 6803. Immunoblotting analysis demonstrated that the purified plasma membrane contained a number of protein components closely associated with the reaction centers of both photosystems. Moreover, these proteins were assembled in the plasma membrane as chlorophyll-containing multiprotein complexes, as evidenced from nondenaturing green gel and low-temperature fluorescence spectroscopy data. Furthermore, electron paramagnetic resonance spectroscopic analysis showed that in the partially assembled photosystem I core complex in the plasma membrane, the P700 reaction center was capable of undergoing light-induced charge separation. Based on these data, we propose that the plasma membrane, and not the thylakoid membrane, is the site for a number of the early steps of biogenesis of the photosynthetic reaction center complexes in these cyanobacterial cells.

Cell Membrane↗
PubMed1972

Distribution of saccharide residues on membrane fragments from a myeloma-cell homogenate: its implications for membrane biogenesis.

Ferritin conjugates of two plant agglutinins, concanavalin A and ricin, have been used as specific electron microscopic stains for covalently-bound saccharide residues on membrane fragments from a myeloma-cell homogenate. The results indicate that different saccharide residues are uniformly localized to a single surface of each membrane fragment. In particular, the ferritin-concanavalin A conjugate binds exclusively to the cisternal side of membrane fragments of the rough endoplasmic reticulum. If it is postulated that the biogenesis of eukaryotic plasma membranes involves an assembly-line process from precursor intracellular membranes, these observed asymmetric distributions of saccharides on cell membranes can be explained.

Animals↗
PubMed1974

Ansamycin biogenesis: studies on a novel rifamycin isolated from a mutant strain of Nocardia mediterranei.

A novel ansamycin, rifamycin W, was isolated from a mutant strain of Nocardia mediterranei. The metabolic origin of rifamycin W was studied by (13)C nuclear magnetic resonance spectroscopy. Examination of the proton-decoupled pulse and Fourier transform (13)C spectra of rifamycin W biogenetically enriched with [1-(13)C]-, [2-(13)C]-, and [3-(13)C]propionate and with [1-(13)C]acetate has revealed that the alignment of acetate and propionate units corresponds to that previously proposed for rifamycin S. Washed mycelium from a rifamycin B-producing strain of N. mediterranei transformed rifamycin W into rifamycin B. We suggest that rifamycin W is a normal intermediate in the biosynthesis of the other rifamycins. These results, together with the structural similarity of rifamycin W to the streptovaricins, reinforce our hypothesis that a common progenitor is involved in the biogenesis of all naphthalenic ansamycins.

Carbon Isotopes↗
PubMed1978

Biogenesis of peroxisomes: intracellular site of synthesis of catalase and uricase.

The intracellular site of synthesis of two peroxisomal enzymes of rat liver, uricase (urate:oxygen oxidoreductase, EC 1.7.3.3) and catalase (hydrogen peroxide:hydrogen peroxide oxidoreductase, EC 1.11.1.6), has been localized on free ribosomes and not membrane-bound ribosomes. Free polysomes and membrane-bound polysomes, prepared by classical cell fractionation techniques from rat liver, were incubated for protein synthesis in a cell-free system derived from rabbit reticulocytes. Characterization of the total translation products by polyacrylamide gel electrophoresis in sodium dodecyl sulfate, as well as by immunoprecipitation with anti-rat albumin anti-serum, confirmed that good separation of the two polysome classes was achieved. Uricase and catalase were immunoprecipitable from translation products directed by free polysomes or phenol-extracted free polysomal mRNA but not from products of membrane-bound polysomes. Furthermore, unlike albumin, nascent uricase and catalase were not cotranslationally segregated by dog pancreas microsomal membranes. The results indicate that uricase and catalase are transferred to the interior of peroxisomes by a post-translational mechanism; an hypothesis is formulated here for the biogenesis of peroxisomes.

Animals↗
PubMed1979

Membrane biogenesis: cotranslational integration of the bacteriophage f1 coat protein into an Escherichia coli membrane fraction.

The coat protein (CP) of bacteriophage f1 is integrated into an Escherichia coli plasma membrane fraction consisting of inverted vesicles when it is synthesized in a cell-free, coupled transcription--translation system supplemented with the inverted vesicles. By using proteolytic enzymes as probes, we found by subsequent peptide mapping and determination of the sequence of the proteolytic products that CP was inserted into the inverted vesicles in an orientation indistinguishable from that in inverted vesicles prepared from infected E. coli: only a COOH-terminal portion of approximately 10 residues was accessible to proteolysis, whereas the remainder of CP (CP') was entirely protected. Protection of CP' was dependent on the integrity of the vesicle membrane, because it was abolished when proteolysis was done in the presence of nonionic detergents. Insertion was observed when the inverted vesicles were present during translation in the cell-free system, not when they were added after translation. Thus, the asymmetric insertion of this type of integral membrane protein is strictly coupled to translation. These findings are discussed with respect to prokaryotic membrane biogenesis and are related to bacteriophage f1 assembly and infection.

Bacterial Proteins↗
PubMed1979

Splicing as a requirement for biogenesis of functional 16S mRNA of simian virus 40.

Simian virus 40 deletion mutants were constructed lacking specifically the intervening sequences for a late viral mRNA. The construction method involved the replacement of portions of the late simian virus 40 genes with the DNA segment from reverse transcription of the viral mRNAs. Restriction endonuclease cleavage and sequence analysis confirmed the precise structure of the mutant DNAs and demonstrated that they contained the genetic information for VP1, including all potential 5' ends for the late viral RNAs. Thus, the primary late transcription product(s) of this mutant should have the structure of functional 16S mRNAs. Complementation analysis as well as immunoprecipitation showed, however, that deletion of the intervening sequences from this mutant prevented the expression of VP1. The nature of this failure appears to be a defect in the posttranscriptional processing of the viral RNA. These results indicate that splicing is an essential function in the biogenesis of certain mRNAs.

Animals↗
PubMed1980

Cellulose biogenesis: Polymerization and crystallization are coupled processes in Acetobacter xylinum.

Calcofluor White ST, stilbene derivative used commerically as an optical brightener for cellulose, increased the rate of glucose polymerization into cellulose by resting cells of the gram-negative bacterium Acetobacter xylinum. This bacterium normally produces a ribbon of cellulose that is a composite of crystalline microfibrils. In concentrations above 0.1 mM, Calcofluor disrupts the assembly of crystalline cellulose I microfibrils and their integration into a composite ribbon by stoichiometric binding to glucose residues of newly polymerized glucan chains. Under these conditions, the rate of glucose polymerization increases up to 4 times the control rate, whereas oxygen uptake increases only 10-15%. These observed effects are readily reversible. If free Calcofluor is washed away or depleted below the threshold value by binding to cellulose as polymerization continues, ribbon production and the normal rate of polymerization resume. It is concluded that polymerization and crystallization are cell-directed, coupled processes and that the rate of crystallization determines the rate of polymerization. It is suggested that coupling must be maintained for biogenesis of crystalline cellulose I.

Journal Article↗
PubMed1982

Animal cells dependent on exogenous phosphatidylcholine for membrane biogenesis.

A Chinese hamster ovary cell (CHO) mutant (strain 58), defective in CDP-choline synthetase (cholinephosphate cytidylyltransferase; CTP:cholinephosphate cytidylyltransferase, EC 2.7.7.15), is temperature sensitive for growth and contains less than half of the normal amount of phosphatidylcholine under nonpermissive conditions [Esko, J. D. & Raetz, C. R. H. (1980) Proc. Natl. Acad. Sci. USA 77, 5192-5196]. We now report that the addition of 40 microM egg phosphatidylcholine or lysophosphatidylcholine to the medium suppresses the temperature sensitivity of mutant 58 and permits the growth of colonies at the restrictive temperature. Phospholipids with different polar headgroups, lipoprotein-bound phospholipids, sphingomyelin, and glycerophosphocholine do not support prolonged growth at 40 degrees C, whereas phosphatidylcholine analogs such as phosphatidyldimethylethanolamine, D-phosphatidylcholine, and beta-phosphatidylcholine are quite effective. A broad range of saturated phosphatidylcholines, especially those with fatty acids 12-18 carbons in length, suppresses the phenotype. Phospholipids containing ether-linked hydrocarbons are ineffective, whereas polyunsaturated phosphatidylcholines are toxic. Residual endogenous synthesis of phosphatidylcholine by the mutant is not stimulated under conditions of phenotypic bypass, but the uptake of exogenous lipid is enhanced considerably compared to the wild type. Our findings demonstrate that exogenous phospholipid can provide at least 50% of the phosphatidylcholine required for membrane biogenesis in animal cells and that uptake of exogenous phospholipids may be regulated.

Animals↗
PubMed1984

Plasma membrane biogenesis in eukaryotic cells: translocation of newly synthesized lipid.

We examined the transfer of sterols and phospholipids from their site of synthesis to the plasma membrane of Acanthamoeba castellanii. Cells were labeled with [3H]acetate, and plasma membrane fractions were isolated under conditions that minimize the nonspecific exchange of lipids between subcellular membrane fractions. Sterols and phospholipids were purified from both whole-cell homogenates and isolated plasma membrane. In whole cells, 3H-labeled lipids were formed, with no apparent time lag, in a linear manner up to 1 hr. Labeled sterol and phospholipids appeared in the plasma membrane, after a 30-min lag, at approximately the same rate. However, the ratio of newly synthesized sterol to phospholipid was significantly enriched in the plasma membrane relative to the whole cell, even at the earlier time points. Pulse-chase experiments indicated that sterols and phospholipids are turned over in the plasma membrane with similar, rather short half-lives. The results of these studies suggest that, although sterols and phospholipids are transported to the cell surface with similar kinetics, some sorting of the lipids must occur at an early stage in membrane biogenesis. The data are consistent with a model of lipid translocation by vesicular transport.

Acetates↗
PubMed1986

Biogenesis of the nuclear lamina: in vivo synthesis and processing of nuclear protein precursors.

Utilizing antibodies against lamins A, B1, and B2, we have studied the biogenesis of the nuclear lamina in chicken embryo fibroblasts. (Lamins B1 and B2 have been identified recently as structurally distinct "lamin B" proteins.) We demonstrate that, unique among the nuclear proteins studied to date, lamin A is synthesized as a higher molecular mass precursor. A short-lived higher molecular mass variant (t 1/2 approximately equal to 3 min) accompanying the mature-size protein was also detected in the case of lamin B2 biosynthesis, but no precursor was found for lamin B1. By combining pulse-chase experiments with subcellular fractionation, we provide evidence that synthesis of lamin proteins occurs on free polysomes; subsequently, the newly synthesized proteins become rapidly associated with a crude nuclear fraction. The lamin A precursor is processed within the nucleus with a half-time of about 30 min. Concomitantly, lamin proteins acquire a characteristic resistance to detergent extraction, suggesting their insertion into a submembraneous protein network. The described biogenetic pathway involving precursor synthesis and processing is very unusual for nuclear proteins; it may have interesting implications for the mechanisms of transport and assembly of poorly soluble nuclear proteins.

Animals↗
PubMed1987

Sources of propionate for the biogenesis of ethyl-branched insect juvenile hormones: Role of isoleucine and valine.

Corpora allata from adult female Manduca sexta biosynthesize the sesquiterpenoid juvenile hormone (JH) III and the unusual ethyl-branched homologue JH II in vitro. We maintained corpora allata in medium 199 using [methyl-(3)H]methionine as the source of the JH methyl ester moiety and as a mass marker. This allowed measurement of the relative contributions of (14)C-labeled precursors to the biogenesis of JH II and III carbon skeletons. We showed efficient incorporation of a propionate equivalent, from isoleucine or valine catabolism, into the ethyl-branched portion of JH II, using double-label liquid scintillation counting of isolated JHs and gas chromatography/mass spectrometry with selected ion monitoring of JH deuteromethoxyhydrin derivatives. Methionine was a poor source of propionate for JH II biosynthesis, while glucose, succinate, threonine, and beta-alanine did not contribute propionate at all. Leucine, isoleucine, and glucose incorporated into JH III and the acetate-derived portion of JH II.

Journal Article↗