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F Gibson

Publications and source records attributed to F Gibson.

At least 55 records · Page 3Linked to original sources
PubMed1994

The cydD gene product, component of a heterodimeric ABC transporter, is required for assembly of periplasmic cytochrome c and of cytochrome bd in Escherichia coli.

The cydD gene of Escherichia coli encodes a protein which, together with the CydC protein, probably constitutes a heterodimeric, ABC-family membrane transporter, necessary for biosynthesis of the cytochrome bd quinol oxidase. Here, we demonstrate that a cydD mutant also fails to synthesise periplasmic c-type cytochrome(s), suggesting that the transporter exports haem or some other component involved in assembly of cytochromes that are found in, or exposed to, the periplasm. The CydDC system appears to be the first example of a transporter required for periplasmic cytochrome assembly processes requiring more than one type of haem. A mutant defective in trxB (adjacent to the cydDC operon, and encoding thioredoxin reductase) was unaffected in cytochrome c or bd assembly.

Adenosine Triphosphatases↗
PubMed1994

Effects of pituitary-gonadal suppression with a gonadotrophin-releasing hormone agonist on fetal gonadotrophin secretion, fetal gonadal development and maternal steroid secretion in the sheep.

In order to investigate the regulation of the hypothalamo-pituitary-gonadal axis during fetal development, sheep fetuses at day 70 of gestation were implanted subcutaneously with a biodegradable implant containing the long-acting gonadotrophin-releasing hormone (GnRH) agonist, buserelin. The treatment of fetuses with a GnRH agonist throughout the last half of gestation (term = 145 days) abolished the increase in plasma LH concentrations that was seen in 2-day-old control lambs in response to an injection of GnRH. This attenuated response was associated with corresponding reductions in the pituitary content of LH and FSH. Immunolocalization studies revealed that pituitary glands from newborn lambs implanted with a GnRH agonist during fetal development were devoid of immunopositive LH- and FSH-containing cells. At birth the testicular weights of GnRH agonist-treated ram lambs were significantly decreased by 40% when compared with controls. This was associated with a 45% reduction in the total number of Sertoli cells per testis. In newborn ewe lambs GnRH agonist treatment had no effect on ovarian weight or on the morphological appearance of the ovaries. GnRH agonist treatment had no effect on the plasma concentrations of progesterone and oestrone in the maternal circulation or on the length of gestation. These results show (1) that GnRH positively regulates the synthesis and secretion of gonadotrophins in the fetus, (2) that reduced fetal gonadotrophic support during the last half of gestation results in a reduction in testicular growth, and (3) that fetal gonadotrophins do not affect maternal steroid secretion.

Animals↗
PubMed1994

Isolation of conserved sequences from yeast artificial chromosomes by exon amplification.

Exon amplification is a technique designed to solve a central problem in mammalian molecular genetics--specifically, the isolation of genes from large regions of genomic DNA. This technique allows exons to be isolated from genomic DNA following the selective removal of introns by the eukaryotic splicing mechanism. It is a relatively rapid procedure and can theoretically be applied to test the coding potential of very long stretches of genomic DNA. In this paper we describe the application of exon amplification to a mouse yeast artificial chromosome (YAC) 175 kb in length. A number of potential coding sequences were amplified, and two sequences were shown to be conserved across a wide variety of species representing potential genes.

Animals↗
PubMed1993

The role of arginine in the conserved polar loop of the c-subunit of the Escherichia coli H(+)-ATPase.

The Arg-41 of the c-subunit of the F0F1-ATPase of Escherichia coli has been changed by site-directed mutagenesis to Glu, Leu or Lys. None of the mutants can carry out oxidative phosphorylation. No detectable F1-ATPase activity is found on the membranes and only small amounts in the cytoplasm. Two-dimensional gel electrophoresis shows that in all three mutant strains the assembly of the F0F1-ATPase has been affected. When plasmids carrying the mutant genes, together with other normal unc genes, were inserted into strains each carrying a mutation in one of the unc genes other than uncE their capacity for oxidative phosphorylation was reduced or eliminated, the effect being most pronounced with the uncG and uncC mutants and least pronounced with the plasmid giving the Arg-->Lys substitution. The c-subunit is a multimer in the ATP synthase complex and it appears that a mixture of normal and mutant gene products allows assembly of a functional complex.

Arginine↗
PubMed1993

Mutants of Escherichia coli affected in respiration: the cloning and nucleotide sequence of ubiA, encoding the membrane-bound p-hydroxybenzoate:octaprenyltransferase.

A mutant of Escherichia coli has been isolated that is unable to grow aerobically on non-fermentable substrates, but able to grow anaerobically on glycerol with alternative electron acceptors such as fumarate. Nitrate as electron acceptor supports anaerobic growth on glycerol, but not on succinate or lactate. Oxygen consumption rates by cell-free extracts with succinate, lactate or glycerol 3-phosphate as substrates were low relative to activities in an isogenic control strain but were restored in vitro by adding ubiquinone-1. Transformation of the mutant with a cloned 2.6 kb ClaI-PvuII fragment of chromosomal DNA restored cellular quinone levels and growth on succinate. The plasmid also complemented a previously isolated ubiA mutant for aerobic growth on non-fermentable substrates. The nucleotide sequence of the cloned fragment revealed a fragment of plsB (91.7 min on the E. coli chromosome map) and three open reading frames (ORFs), one of which (ORF3) encodes a protein with a predicted molecular mass of 32511 Da. The hydrophobicity profile of the ORF3 protein is characteristic of a membrane protein with five hydrophobic regions and is very similar to that of the Saccharomyces cerevisiae COQ2 gene product (p-hydroxybenzoate:polyprenyltransferase, required for the second step of ubiquinone biosynthesis) and to the product of the E. coli cyoE gene. Complementation of ubi mutants with various deletion derivatives of the cloned DNA fragment confirms that ORF3 is ubiA. ORF3 is closely linked to ubiC (ORF2), which encodes chorismate lyase.

Alkyl and Aryl Transferases↗
PubMed1993

Cytochrome bd biosynthesis in Escherichia coli: the sequences of the cydC and cydD genes suggest that they encode the components of an ABC membrane transporter.

At least four genes are known to affect formation of the cytochrome bd-type terminal oxidase of Escherichia coli. In addition to the genes (cydA and cydB) encoding the two constituent subunits of this complex, a further two genes (cydC and cydD) map near 19 min on the E. coli chromosome. We report here the cloning of both genes on a 5.3 kb ClaI-HindIII restriction fragment, which, when used to transform either a cydC or cydD mutant, restored the ability of these mutants to grow on a selective medium containing azide and zinc ions and also restored the spectral signals associated with the cytochrome components of the oxidase complex. A subcloned 1.8 kb DdeI fragment similarly restored growth and cytochrome content of a cydD mutant, but not a cydC mutant. The complete nucleotide sequence of the ClaI-HindIII fragment reveals three open reading frames, one being trxB (19.3 min on the E. coli chromosome map, encoding thioredoxin reductase), confirming the mapping position of cydD previously established by P1-mediated transduction. Two ORFs identified by complementation experiments as cydD and cydC encode proteins with predicted molecular masses, respectively, of 65,103 and 62,946 Da. The hydropathy profile of each protein reveals an N-terminal hydrophobic domain and a C-terminal hydrophilic domain containing a putative nucleotide-binding site. The gene products probably constitute an ABC (ATP-binding cassette) family membrane transporter, the function of which is necessary for the formation of the cytochrome bd quinol oxidase. The CydDC system appears to be the first prokaryotic example of a heterodimeric ABC transport system in which each polypeptide contains both hydrophobic and ATP-binding domains.

ATP-Binding Cassette Transporters↗
PubMed1992

Isolation and characterization of Escherichia coli mutants affected in aerobic respiration: the cloning and nucleotide sequence of ubiG. Identification of an S-adenosylmethionine-binding motif in protein, RNA, and small-molecule methyltransferases.

We report the isolation and characterization of a mutant of Escherichia coli unable to grow aerobically on non-fermentable substrates, except for very slow growth on glycerol. The mutant contains cytochrome oxidases o and d, and grows anaerobically with alternative electron acceptors. Oxygen consumption rates of cell-free extracts were low relative to activities in an isogenic control strain, but were restored in vitro by adding ubiquinone-1 to cell-free extracts. Transformation with a cloned 2.8 kb ClaI-EcoRV fragment of chromosomal DNA restored the ability of this mutant (AN2571) to grow on succinate and also restored cellular quinone levels in this strain. The plasmid also complemented a previously isolated ubiG mutant (AN151) for aerobic growth on succinate. The nucleotide sequence revealed a 0.7 kb portion of gyrA. Unidirectional nested deletions from this fragment and complementation analysis identified an open reading frame encoding a protein with a predicted molecular mass of 26.5 kDa. This gene (ubiG) encodes the enzyme 2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone methyltransferase, which catalyses the terminal step in the biosynthesis of ubiquinone. The open reading frame is preceded by a putative Shine-Dalgarno sequence and followed by three palindromic unit sequences. Comparison of the inferred amino acid sequence of UbiG with the sequence of other S-adenosylmethionine (AdoMet)-dependent methyltransferases reveals a highly conserved AdoMet-binding region. The cloned 2.8 kb fragment also contains a sequence encoding the C-terminus of a protein with 42-44% identity to fungal acetyl-CoA synthetases.

Aerobiosis↗
PubMed1992

Prostaglandin E2 enhances AVP-stimulated but not CRF-stimulated ACTH secretion from cultured fetal sheep pituitary cells.

This study examined the ability of prostaglandin E2 (PGE2) to regulate ACTH secretion from cultured anterior pituitary cells of fetal sheep between days 130 and 140 of gestation (term = 145 days). Corticotrophin-releasing factor (CRF) and arginine vasopressin (AVP) induced dose-dependent (0.1-1000 nmol/l) increases in ACTH secretion from fetal sheep pituitary cells maintained in culture for 6 days, with AVP being significantly (P less than 0.01) more potent than CRF. PGE2 (1000 nmol/l) significantly (P less than 0.05) enhanced the ability of AVP, but not CRF, to stimulate ACTH secretion. However, PGE2 given alone (0.1-1000 nmol/l) had no effect on ACTH secretion. Concomitant administration of CRF and AVP induced a greater release of ACTH than after treatment with either peptide alone, a synergistic interaction which was unaffected by simultaneous administration of PGE2. These results provide evidence for a direct action of PGE2 on ACTH secretion from the fetal sheep pituitary gland via a specific interaction with AVP. This interaction may allow increased fetal plasma concentrations of PGE2, seen during late gestation, to stimulate fetal pituitary-adrenal maturation.

Adrenocorticotropic Hormone↗
PubMed1992

Neuroendocrine regulation of sheep fetuses.

During fetal development the neuroendocrine system plays a pivotal role in the regulation of normal intrauterine development, growth and differentiation and the onset of birth. Studies on the ontogenic development of neuroendocrine function in sheep fetuses are discussed with particular reference to the differential regulation of the pituitary-gonadal and pituitary-adrenal axis. Fetal pituitary-gonadal activity increases to a maximum at mid-gestation and is suppressed just before birth. Using immunocytochemistry, we have examined the ontogeny of gonadotroph development in the pituitary of female sheep fetuses. At day 70 of gestation (term = 145 days) only immunopositive luteinizing hormone beta (LH beta) cells were present. The number and intensity of staining of these LH beta cells increased by day 100 and declined again by day 130. Immunopositive alpha-subunit and follicle-stimulating hormone beta (FSH beta) cells appeared by day 100 of gestation and had further increased in number and staining intensity by day 130. Treatment of fetuses with the gonadotrophin-releasing hormone (GnRH) agonist, buserelin, from day 70 of gestation results in desensitization of the fetal pituitary gonadotrophs, suppression of pituitary gonadotrophin mRNA and a reduction in the number of immunopositive gonadotrophin-containing cells. Thus, in sheep fetuses the development of cells containing LH and FSH depends critically on an appropriate GnRH signal from the fetal hypothalamus. In contrast, hypothalamo-pituitary-adrenal activity increases during gestation to reach a maximum before birth. This is characterized by a progressive increase in fetal plasma adrenocorticotrophic hormone (ACTH) and cortisol concentrations, and a high frequency of ACTH and cortisol pulses in the final hours before parturition. Steady state concentrations of pro-opiomelanocortin (POMC) mRNA increase throughout fetal development but decline dramatically in the final days before birth, when ACTH concentrations are at a maximum. This decline in POMC expression is probably the result of the negative feedback effects of high cortisol concentrations. The neuroendocrine mechanisms that mediate the pulsatile secretion of ACTH at this crucial time are complex and as yet incompletely defined. However, the opioid antagonist, naloxone, suppresses the secretion of ACTH during the final days before birth, thus providing evidence for the tonic regulation of ACTH secretion by stimulatory endogenous opioids. Prostaglandins that are secreted from the placenta during late gestation stimulate fetal ACTH, but not gonadotrophin secretion, whereas placental steroids are thought to inhibit fetal gonadotrophin secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocorticotropic Hormone↗
PubMed1991

The chloroplast beta-subunit allows assembly of the Escherichia coli F0 portion of the energy transducing adenosine triphosphatase.

The effect of the expression of the chloroplast F1-ATPase beta-subunit in two Escherichia coli beta-subunit mutant strains was investigated. The amount of chloroplast beta-subunit formed in E. coli was increased by introducing a 'Shine-Dalgarno' sequence upstream from the translation start site. The chloroplast beta-subunit was membrane bound but was unable to functionally replace the mutant beta-subunit in a strain carrying the uncD409 allele [corrected]. However, in an E. coli mutant strain unable to form the beta- and epsilon-subunits the presence of the chloroplast beta-subunit enabled the assembly of a functional proton pore [corrected]

Base Sequence↗
PubMed1990

The chloroplast CF0I subunit can replace the b-subunit of the F0F1-ATPase in a mutant strain of Escherichia coli K12.

The amino acid sequence of the CF0I subunit from the chloroplast F0F1-ATPase has only a low similarity to the amino acid sequence of the b-subunit of the E. coli F0F1-ATPase. However, secondary and tertiary structure predictions plus the distribution of hydrophobic and hydrophilic amino acids have indicated that these two subunits serve a similar function. This proposition was investigated directly. A cDNA clone for the chloroplast atpF gene, encoding the CF0I subunit, was altered by site-directed mutagensis such that the translation start site corresponded to the N-terminus of the mature protein. An E. coli mutant strain carrying a chain-terminating mutation in the uncF gene, encoding the b-subunit, was transformed with the plasmid carrying the altered atpF gene. The resultant transformant was able to grow on succinate and gave a growth yield similar to that of a wild-type control. Assays on membrane preparations from the transformant also clearly indicated that the mature CF0I subunit from spinach chloroplasts was able to replace the E. coli b-subunit in the E. coli F0F1-ATPase.

Amino Acid Sequence↗
PubMed1990

Mutational analysis of the function of the a-subunit of the F0F1-APPase of Escherichia coli.

In a model proposed for the structure of the a-subunit of the Escherichia coli F0F1-ATPase (Howitt, S.M., Gibson, F. and Cox, G.B. (1988) Biochim. Biophys. Acta 936, 74-80), a cluster of charged residues, including one arginine and four aspartic acid residues, lie on the periplasmic side of the membrane. On the cytoplasmic side, three pairs of lysine residues and an arginine residue are present. Site-directed mutagenesis was used to investigate the roles of these residues. It was found that none was directly involved in the proton pore. However, the substitutions of Asp-124 or Asp-44 by asparagine or Arg-140 by glutamine had similar effects in that the membranes from such mutants from which the F1-ATPase was removed were proton-impermeable. A combination of the Asp-44 mutation with either the Asp-124 or Arg-140 mutations in the same strain resulted in complete loss of oxidative phosphorylation. It was tentatively concluded that Asp-124 and Arg-140 form a salt bridge, as did Asp-44 with an unknown residue, and these salt bridges were concerned with the maintenance of correct a-subunit structure. Further support for this conclusion was obtained when second site revertants of a Glu-219 to histidine mutant were found to have either histidine or leucine replacing Arg-140. Thus, the lack of the Asp-124/Arg-140 salt bridge might enable repositioning of the helices of the a-subunit such that His-219 becomes a functional component of the proton pore.

Base Sequence↗
PubMed1990

Pre-eclampsia is associated with HLA-DR4 sharing between mother and fetus.

Full HLA-A,B and DR typing was carried out on 92 women with proteinuric pre-eclampsia, 80 of their husbands and 46 of their babies. The results were compared with corresponding data from 65 normotensive pregnancies involving primiparous women. The frequency of HLA-DR4 was increased in the pre-eclamptic women (RR 3.1; p less than 0.005) and in the babies of pre-eclamptic pregnancies (RR 2.6; p less than 0.03). The strongest association, however, was with sharing of HLA-DR4 between mother and fetus (RR 4.2; p = 0.01). There was no increase in HLA antigen sharing in general between spouses or maternal-fetal pairs in pre-eclampsia. Nor did pre-eclamptic women exhibit increased homozygosity in general at any HLA locus. We conclude that genetic susceptibility to pre-eclampsia depends at least partly on fetomaternal compatibility for a gene or genes associated with HLA-DR4.

Female↗
PubMed1989

Association between susceptibility to pre-eclampsia within families and HLA DR4.

56 women who had had proteinuric pre-eclampsia and who had parous sisters were studied. In first pregnancy, proteinuric pre-eclampsia was more common in the sisters than in the maternity hospital population (8/71 [11%] vs 41/1978 [2%]); the relative risk was 6.0. The frequency of HLA DR4 was higher in sisters with pregnancy-induced hypertension than in sisters with normotensive pregnancies (8/18 [44%] vs 10/54 [19%]) and more of them shared HLA DR4 with their spouses (4/14 [29%] vs 0/29). Genetic susceptibility to pre-eclampsia is associated with HLA DR4; it may be conferred by fetomaternal sharing of a single recessive HLA-linked gene.

Adult↗
PubMed1989

The cytochrome oxidases of Bacillus subtilis: mapping of a gene affecting cytochrome aa3 and its replacement by cytochrome o in a mutant strain.

A mutant of Bacillus subtilis has been isolated that fails to grow on succinate as the source of carbon, yet grows on glucose. Intact cells of the mutant and cytoplasmic membranes derived therefrom lack cytochromes a and a3 but contain a cytochrome o-like pigment, which forms a photodissociable compound with CO and is reactive with oxygen. The mutation in the genome has been located and lies at about 130 degrees on the chromosomal map between the metC and pyrD loci. The designation cox is suggested for this gene.

Bacillus subtilis↗
PubMed1989

Mutations affecting the cytochrome d-containing oxidase complex of Escherichia coli K12: identification and mapping of a fourth locus, cydD.

A mutant of Escherichia coli K12 has been isolated affected in a gene, designated cydD, distinct from the three previously described loci involved in the synthesis of assembly of the cytochrome bd oxidase complex. The mutant, obtained by nitrosoguanidine mutagenesis, lacks the spectroscopically detectable components of this oxidase, namely cytochromes b558, b595 and d. Cytochrome oxidase o is the sole CO-binding cytochrome in membranes of the mutant, but the soluble haemoprotein b-590 and catalase activity appear unaffected. Discrimination between Cyd+ and Cyd- strains is facilitated by the development of a defined low-phosphate medium that allows the inclusion of Zn2+ as well as azide, inhibitors of respiratory electron transfer particularly via cytochrome o. Mapping with F-prime factors and by P1 cotransductional frequencies shows the mutation to map near 19.3 min on the E. coli chromosome, distinct from cydC, which maps at 18.9 min. The gene order in this region was tested in a three-factor cross and demonstrates the order zbj::Tn10(YYC199)-cydD-aroA, consistent with cotransduction frequencies.

Bacterial Proteins↗