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PubMed2001

Characterization of the CsfC and CsfD proteins involved in the biogenesis of CS5 pili from enterotoxigenic Escherichia coli.

The region required for biosynthesis of CS5 pili consists of six csf genes, with csfA encoding the major subunit. In this study, we describe the characterization of two of the genes constituting the region, csfC and csfD, but also identify the true morphology of the CS5 pilus by high resolution electron microscopy. CsfD was shown to be essential in the initiation of CS5 pilus biogenesis, did not possess any chaperone-like activity for the major subunit, and was an integral minor component of the pilus structure. Studies on CsfD translocation across the outer membrane in Escherichia coli K-12 using a csfA mutant also showed that CsfD is likely to be the first pilin subunit assembled. A specific in-frame deletion in the csfC gene resulted in the complete absence of cell surface CS5 pili and prevented the translocation of CsfA and CsfD pilins across the outer membrane. Specific cell localization studies showed an accumulation of CsfC in the outer membranes of E. coli K-12, while complementation experiments with homologous outer membrane assembly genes from CS1 and CFA/I pili systems were unable to restore assembly of CS5 pili. The CS5 pilus was shown to be a 2 nm flexible fibrillar structure, which adopted a predominantly open helical conformation under the electron microscope.

Bacterial Outer Membrane Proteins↗
PubMed2001

Oxidation of Abeta and plaque biogenesis in Alzheimer's disease and Down syndrome.

The processes involved with beta-amyloid (Abeta) degradation and clearance in human brain are not well understood. We hypothesized that the distribution of oxidatively modified Abeta, as determined by an affinity-purified antibody in the entorhinal and frontal cortices of Alzheimer's disease (AD), Down syndrome (DS), nondemented elderly control cases, and canine brain, would provide insight into the mechanisms of Abeta accumulation. Based upon plaque counts, oxidized Abeta was present within 46-48% of diffuse and primitive plaques and 98% of cored plaques. Dense punctate deposits of oxidized Abeta were distributed throughout the neuropil in AD and DS brains but were also present within controls with mild neuropathology and isolated cognitive impairments. Confocal studies indicate that punctate oxidized Abeta deposits were within activated microglia. Oxidatively modified Abeta may reflect the efforts of microglial cells to take up and degrade Abeta. Oxidative modification of Abeta may be an early event in Abeta pathogenesis and may be important for plaque biogenesis.

Alzheimer Disease↗
PubMed1993

The 70 kDa peroxisomal membrane protein: an ATP-binding cassette transporter protein involved in peroxisome biogenesis.

The 70 kDa peroxisomal membrane protein (PMP70) is a major component of peroxisomal membranes. cDNAs for human and rat PMP70 have been cloned and sequenced and the gene mapped to human chromosome 1p21-22. The predicted amino acid sequence showed homology to members of the ATP-binding cassette transporter family. In humans, mutations in the PMP70 gene have been found in a subset of patients with Zellweger syndrome, a lethal inborn error of peroxisome biogenesis. These results suggest that PMP70 functions in transporting molecules or possibly peptides across the peroxisomal membrane and has an important role in peroxisome assembly.

ATP-Binding Cassette Transporters↗
PubMed1994

The highly edited orf206 in Oenothera mitochondria may encode a component of a heme transporter involved in cytochrome c biogenesis.

A highly transcribed region in Oenothera mitochondria codes for a reading frame (orf206) which shows high homology to the Marchantia encoded mitochondrial open reading frame orf277 and is also conserved in the mitochondrial genomes of Arabidopsis thaliana and Daucus carota. Transcripts of orf206 are modified by cytidine to uridine changes in 46 positions by RNA editing, affecting 30% of all cytidines and 15% of the total encoded amino acids. This ORF is cotranscribed with an upstream reading frame and with the downstream rps 14 gene. The orf206 deduced protein shows high similarity to polypeptides which are proposed to be part of an ABC-type heme transporter involved in cytochrome c biogenesis in Bradyrhizobium and Rhodobacter.

Amino Acid Sequence↗
PubMed1982

Pigment biogenesis in freshwater shrimp ventral nerve chord chromatophores.

The possible biogenesis of two pigment granule types present in the monochromatic, brown chromatosomes enveloping the ventral nerve chord of the freshwater palaemonid shrimps Macrobrachium acanthurus, M. heterochirus and M. olfersii is examined by transmission electron microscopy in thin section and freeze fracture replicas. Prominent, membrane limited granules are suggested to have their origin in a complex, juxtanuclear, smooth endoplasmic reticulum labyrinth, continuous with the nuclear envelope. Amembranous, lipocarotenoid granules possibly derive from the external surface of the smooth endoplasmic reticulum. Nuclear envelope and SER membranes contain numerous 11 nm diameter intramembranous particles while pigment granule membranes exhibit fewer particles. A dictyosomal origin for the lipocarotenoid granules is discounted. Granulogenesis is suggested to be a continuous process in crustacean chromatophores.

Animals↗
PubMed1992

The influence of congo red on the cell wall and (1----3)-beta-D-glucan microfibril biogenesis in Saccharomyces cerevisiae.

Congo red was applied to growing yeast cells and regenerating protoplasts in order to study its effects on wall biogenesis and cell morphogenesis. In the presence of the dye, the whole yeast cells grew and divided to form chains of connected cells showing aberrant wall structures on both sides of the septum. The wall-less protoplasts in solid medium with the dye exhibited an abnormal increase in volume, regeneration of aberrant cell walls and inability to carry out cytokinesis or protoplast reversion to cells. In liquid medium, the protoplasts synthesized glucan nets composed mainly of thin fibrils orientated at random, whereas normally, in the absence of dye, the nets consist of rather thick fibrils, 10 to 20 nm in width, assembled into broad ribbons. These fibrils are known to consist of triple 6/1 helical strands of (1----3)-beta-D-glucan aggregated laterally in crystalline packing. The thin fibrils (c. 4 to 8 nm wide) can contain only a few triple helical strands (c. 1.6 nm wide) and are supposed to be prevented from further aggregation and crystallization by complexing with Congo red on their surfaces. Some loose triple 6/1 helical strands (native elementary fibrils) are also discernible. They represent the first native (1----3)-beta-D-glucan elementary fibrils depicted by electron microscopy. The effects of Congo red on growth and the wall structure in normal cells and regenerating protoplasts in solid medium can be explained by the presence of a complex which the dye forms with (helical) chain parts of the glucan network and which results in a loss of rigidity by a blocked lateral interaction between the helices.

Cell Division↗
PubMed1993

A plant mitochondrial gene encodes a protein involved in cytochrome c biogenesis.

Analysis of a transcribed region in the mitochondrial genome of Oenothera revealed an open reading frame (ORF) of 577 codons (orf577) that is also conserved in carrot, here encoding a protein of 579 amino acids (orf579). RNA editing alters the mRNA sequence of orf577 in Oenothera with 46 C to U transitions, many of which improve sequence similarity with the homologous Marchantia gene orf509. The deduced polypeptides show significant similarity with the ccl1-encoded protein involved in cytochrome c biogenesis in the photosynthetic bacterium Rhodobacter capsulatus. A highly conserved domain is also found in plastid ORFs, suggesting that these bacterial, chloroplast and mitochondrial genes encode polypeptides with analogous functions in assembly and maturation of cytochromes c.

Amino Acid Sequence↗
PubMed1995

The novel nuclear gene DSS-1 of Saccharomyces cerevisiae is necessary for mitochondrial biogenesis.

A previously unknown nuclear gene DSS-1 from Saccharomyces cerevisiae was cloned and sequenced. The gene was isolated as a multicopy suppressor of a disruption of the SUV-3 gene coding for a DEAD/H box protein involved in processing and turnover of mitochondrial transcripts. The DSS-1 gene codes for a 970 amino-acid protein of molecular weight 111 kDa and is necessary for mitochondrial biogenesis. Amino-acid sequence analysis indicates the presence of motifs characteristic for Escherichia coli RNase II, the dis3 protein from Schizosaccharomyces pombe, the cyt4 protein participating in RNA processing and turnover in Neurospora crassa mitochondria, and the vacB protein from Shigella flexneri. We suggest that the DSS-1 protein may be a component of the mitochondrial 3'-5' exoribonuclease complex.

Amino Acid Sequence↗
PubMed1987

Effects of linker insertions on the biogenesis and functioning of the Escherichia coli outer membrane pore protein PhoE.

To study the effects of small insertions on the biogenesis and functioning of outer membrane pore protein PhoE of Escherichia coli K12, oligonucleotides were inserted at five different sites in the phoE gene. The proteins encoded by the mutant alleles all appeared to be incorporated into the outer membrane since cells producing these proteins bound either phages specific for the PhoE protein or monoclonal antibodies or both. However, one mutant protein was apparently not incorporated normally since expression of this protein was lethal and the protein did not function as a pore. Amino acid residues 75 and 280 of the PhoE protein appear to be exposed on the cell surface because insertions at these sites interfere with the binding of PhoE-specific phages or monoclonal antibodies to whole cells, respectively.

Bacterial Outer Membrane Proteins↗
PubMed1993

A gene involved in the biogenesis of c-type cytochromes is co-transcribed with a ribosomal protein gene in wheat mitochondria [corrected].

Sequence analysis of a transcribed region of the wheat mitochondrial (mt) genome revealed two open reading frames (orfs) coding for proteins of 589 and 174 amino acids. Both genes are co-transcribed in a 2.6-kb RNA. The largest orf codes for a hydrophobic protein which bears similarity to a bacterial protein involved in the biogenesis of c-type cytochromes. Its corresponding RNA sequence is fully edited at 34 positions. The second orf encodes a protein homologous to the amino-terminal third of E. coli ribosomal protein S1, corresponding to the ribosome-binding domain of this protein. Its RNA sequence is edited at four positions, one of the edits creating a stop codon. The presence of both proteins in wheat mitochondria was demonstrated using specific antibodies raised against fusion proteins obtained in E. coli from the corresponding cDNAs.

Amino Acid Sequence↗
PubMed1995

The cycHJKL genes of Rhizobium meliloti involved in cytochrome c biogenesis are required for "respiratory" nitrate reduction ex planta and for nitrogen fixation during symbiosis.

We report the genetic and biochemical analysis of Rhizobium meliloti mutants defective in symbiotic nitrogen fixation (Fix-) and "respiratory" nitrate reduction (Rnr-). The mutations were mapped close to the ade-1 and cys-46 chromosomal markers and the mutated locus proved to be identical to the previously described fix-14 locus. By directed Tn5 mutagenesis, a 4.5 kb segment of the chromosome was delimited in which all mutations resulted in Rnr- and Fix- phenotypes. Nucleotide sequence analysis of this region revealed the presence of four open reading frames coding for integral membrane and membrane-anchored proteins. Biochemical analysis of the mutants showed that the four proteins were necessary for the biogenesis of all cellular c-type cytochromes. In agreement with the nomenclature proposed for rhizobial genes involved in the formation of c-type cytochromes, the four genes were designated cycH, cycJ, cycK, and cycL, respectively. The predicted protein product of cycH exhibited a high degree of similarity to the Bradyrhizobium japonicum counterpart, while CycK and CycL shared more than 50% amino acid sequence identity with the Rhodobacter capsulatus Cc11 and Cc12 proteins, respectively. cycJ encodes a novel membrane anchored protein of 150 amino acids. We suggest that this gene cluster codes for (parts of) a multisubunit cytochrome c haem lyase. Moreover, our results indicate that in R. meliloti c-type cytochromes are required for respiratory nitrate reduction ex planta, as well as for symbiotic nitrogen fixation in root nodules.

Amino Acid Sequence↗
PubMed1981

Biogenesis of the C20 polyketide, aflatoxin. A review.

Aflatoxin B2 is a secondary metabolite produced by the ubiquitous molds Aspergillus flavus and Aspergillus parasiticus. The toxin was first characterized in 1963 as the etiological agent responsible for the infamous "Turkey X' disease. Since that time, much information on its chemistry, toxicity and biological activity has accumulated. A significant amount of work has been done to elucidate its biosynthesis. Evidence indicates the polyketide route as its point of origin. The steps involved in the polyketide pathway, the six identified intermediated compounds, and the experimental techniques and analytical instrumentation used to procure information on aflatoxin biogenesis are included in this review.

Acetates↗
PubMed1977

[Lipid metabolism in Aspergillus versicolor (Vuill.) Tiragoschi. Relation to biogenesis of sterigmatocystin].

Aspergillus versicolor is cultivated in a synthetic medium for 22 days. Bioproduction of lipids and sterigmatocystin are compared. The fatty acids of the neutral lipid and polar lipids fractions are mainly: C 16:0, C 18:0, C 18:1, C 18:2, C 18:3. Maximal yields of dry weight, neutral lipids and sterigmatocystin occur, respectively, on the 4th, the 7th and the 20th days. These results and their comparison with other works emphasize that a fall of concentration in lipids precedes the phase of highest concentration in secondary metabolites of polyketide type; it appears that fats and particularly palmitic acid are present in biogenesis of these derivatives.

Aspergillus↗
PubMed1992

Peroxisome biogenesis in Saccharomyces cerevisiae.

The observation that peroxisomes of Saccharomyces cerevisiae can be induced by oleic acid has opened the possibility to investigate the biogenesis of these organelles in a biochemically and genetically well characterized organism. Only few enzymes have been identified as peroxisomal proteins in Saccharomyces cerevisiae so far; the three enzymes involved in beta-oxidation of fatty acids, enzymes of the glyoxylate cycle, catalase A and the PAS3 gene product have been unequivocally assigned to the peroxisomal compartment. However, more proteins are expected to be constituents of the peroxisomes in Saccharomyces cerevisiae. Mutagenesis of Saccharomyces cerevisiae cells gave rise to mutants unable to use oleic acid as sole carbon source. These mutants could be divided in two groups: those with defects in structural genes of beta-oxidation enzymes (fox-mutants) and those with defects in peroxisomal assembly (pas-mutants). All fox-mutants possess morphologically normal peroxisomes and can be assigned to one of three complementation groups (FOX1, 2, 3). All three FOX genes have been cloned and characterized. The pas-mutants isolated are distributed among 13 complementation groups and represent 3 different classes: peroxisomes are either morphologically not detectable (type I) or present but non-proliferating (type II). Mislocalization concerns all peroxisomal proteins in cells of these two classes. The third class of mutants contains peroxisomes normal in size and number, however, distinct peroxisomal matrix proteins are mislocalized (type III). Five additional complementation groups were found in the laboratory of H.F. Tabak. Not all PAS genes have been cloned and characterized so far, and only for few of them the function could be deduced from sequence comparisons. Proliferation of microbodies is repressed by glucose, derepressed by non-fermentable carbon sources and fully induced by oleic acid. The regulation of four genes encoding peroxisomal proteins (PAS1, CTA1, FOX2, FOX3) occurs on the transcriptional level and reflects the morphological observations: repression by glucose and induction by oleic acid. Moreover, trans-acting factors like ADR1, SNF1 and SNF4, all involved in derepression of various cellular processes, have been demonstrated to affect transcriptional regulation of genes encoding peroxisomal proteins. The peroxisomal import machinery seems to be conserved between different organisms as indicated by import of heterologous proteins into microbodies of different host cells. In addition, many peroxisomal proteins contain C-terminal targeting signals. However, more than one import route into peroxisomes does exist.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

Cytosolic compartmentalization of hepatic alanine:glyoxylate aminotransferase in patients with aberrant peroxisomal biogenesis and its effect on oxalate metabolism.

Two patients with atypical manifestations of aberrant peroxisomal biogenesis are described. Contrary to previous studies, which had shown that Zellweger syndrome patients usually have normal levels of urinary oxalate excretion, the patients in the present study had evidence of abnormal oxalate metabolism in the form of hyperoxaluria and, in one of the patients, calcium oxalate urolithiasis. Activity of the liver-specific peroxisomal enzyme alanine:-glyoxylate aminotransferase (AGT), which is a major determinant of the level of endogenous oxalate synthesis in humans, was normal in one patient and markedly supranormal in the other. Using the technique of post-embedding protein A-colloidal gold immunoelectron microscopy, AGT was found to be mainly cytosolic in the livers of both patients, with significant amounts also localized in the nuclei. In a small minority of the hepatocytes of one patient, who was homozygous for the more common (major) AGT allele, large numbers of unidentified fibrillar arrays were found in the cytosol, which labelled heavily for immunoreactive AGT. The background cytosolic AGT labelling was markedly reduced in such cells when compared to the majority of cells that did not contain fibrils. In the other patient, who was heterozygous for the major and minor AGT alleles, there appeared to be low levels of mitochondrial AGT labelling. In the light of these data, the possible metabolic function of cytosolic AGT in the livers of panperoxisomal disease patients is discussed.

Alanine Transaminase↗
PubMed1994

Developmental regulation of mitochondrial biogenesis in Trypanosoma brucei.

The metabolism of Trypanosoma brucei undergoes a significant change as the parasite differentiates from the mammalian bloodstream form to the form found in the tse-tse fly vector. Because the mitochondria of bloodstream form cells lack cytochromes and several key citric acid cycle enzymes, the metabolism of these cells is mostly limited to glycolysis. The reducing equivalents generated by this process are passed to oxygen by a plant-like alternative oxidase. As cells differentiate to the insect form, they begin to oxidatively metabolize proline. The mitochondria of insect form cells contain functional, cytochrome-mediated electron transport chains and have complete complements of citric acid cycle enzymes. Although the characterization is far from complete, the nuclear and mitochondrial genes involved in the expression of these mitochondrial functions appear to be developmentally regulated at posttranscriptional and posttranslational levels. This review outlines some of the molecular processes that are associated with the developmental regulation of mitochondrial biogenesis and suggests some possible mechanisms of regulation.

Animals↗
PubMed1985

Effect of hypothyroidism on the biogenesis of free mitochondria in the cerebral hemispheres and in cerebellum of rat during postnatal development.

The effect of propylthiouracil-induced neonatal hypothyroidism on some aspects of the biogenesis of free (non-synaptosomal) mitochondria in the cerebral hemispheres and in the cerebellum of developing rat has been studied. The results obtained show that in hypothyroid rats mitochondrial DNA synthesis is delayed, mitochondrial RNA synthesis is not affected and cytochrome aa3 content of mitochondria is lower than in controls. Furthermore ultrathin sections of 14- and 21-day old hypothyroid rat cerebella show mitochondria with an altered ultrastructural organization and large intracristal spaces.

Animals↗