Three-dimensional structure of tubular networks, presumably Golgi in nature, in various yeast strains: a comparative study.

Background: In the yeast Saccharomyces cerevisiae, the Golgi apparatus consists of discrete units distributed throughout the cytoplasm. When such units are examined in three dimensions, in relatively thick sections prepared for the electron microscope, they usually appear as small tubular networks with a stained material accumulating in dilations located at the junctions of membranous tubules. To see whether such tubular networks are observed in other yeast species, the three-dimensional structure of organelles in eight additional yeast strains, endowed with diverse biological properties, are examined.

A self-included cyclomaltoheptaose derivative studied by NMR spectroscopy and molecular modelling.

The 3D structure of 6-deoxy-6-L-tyrosinylamidocyclomaltoheptaose, a self-complexing beta-cyclodextrin derivative, was determined by NMR and molecular modelling. The aminoacyl side-chain is included in the cavity and induces chemical-shift variations in the CD proton signals, allowing their complete assignment. Dipolar interactions between protons of the tyrosine ring and internal protons of the cyclodextrin were used to obtain distance constraints.

Nonnative capping structure initiates helix folding in an annexin I fragment. A 1H NMR conformational study.

A 21-residue peptide, P1AQFD5ADELR10AAMKG15LGTDE20D, corresponding to the (helix A)-loop motif of the second repeat of human annexin I, was synthesized and studied by 2D proton NMR. The conformational properties of the peptide were characterized at different temperatures in pure aqueous solution and in a TFE/H2O (1:4 v/v) mixture. In pure aqueous solution, the peptide adopts a preferred conformation, comprising both elements of native and nonnative structures.

Multihormonal regulation of nephron epithelia: achieved through combinational mode?

The kidney is the main organ regulating composition of body fluids. A considerable number of hormones control the activity of renal cells to maintain hydromineral equilibrium. It becomes more and more difficult to interpret this multihormonal control in terms of regulatory processes.

Dam methylase from Escherichia coli: kinetic studies using modified DNA oligomers: hemimethylated substrates.

We have measured steady-state kinetics of the N6-adenine methyltransferase Dam Mtase using as substrates non-selfcomplementary tetradecamer duplexs (d[GCCGGATCTAGACG]-d[CGTCTAGATCC-GGC]) containing the hemimethylated GATC target sequence in one or the other strand and modifications in the GATC target sequence of the complementary strands. Modifications included substitution of guanine by hypoxanthine (I), thymine by uracil (U) or 5-ethyl-uracil (E) and adenine by 2,6-diamino-purine (D). Thermodynamic parameters were obtained from the concentration dependence of the melting temperature (Tm) of the duplexes.

Symmetric structural features and binding site of the primary electron donor in the reaction center of Chlorobium.

The protein binding interactions of the constituent bacteriochlorophyll a molecules of the primary electron donor, P840, in isolated reaction centers from Chlorobium limicola f thiosulphatophilum and the electronic symmetry of the radical cation P840+. were determined using near-infrared Fourier transform (FT) Raman spectroscopy excited at 1064 nm. The FT Raman vibrational spectrum of P840 indicates that it is constituted of a single population of BChl a molecules which are spectrally indistinguishable.

Lumenal Ca2+ dissociation from the phosphorylated Ca(2+)-ATPase of the sarcoplasmic reticulum is sequential.

Once two radioactive Ca2+ coming from the cytoplasm are bound to the transport sites of the nonphosphorylated ATPase, excess EGTA induces rapid dissociation of both ions, whereas excess nonradioactive Ca2+ only reaches one of the two bound Ca2+. This difference has been explained assuming that the two Ca2+ sites are in a single file channel in which the superficial Ca2+ is freely exchangeable from the cytoplasm, whereas the deeper Ca2+ is exchangeable only when the superficial site is vacant. The same experiment was done using phosphorylated ATPase to determine whether Ca2+ dissociation toward the lumen is sequential as well.

Immunogenicity of T epitope-containing cyclic peptides. Increasing neutralizing antibody responses by introducing fine chemical changes.

We showed previously that the disulfide-containing T peptide 24-41 C from a highly structured snake toxin elicits, in a free state, Abs that neutralize the toxin, and only a turn structure commonly exists in 24-41 C and the corresponding toxin region. To tentatively increase the neutralizing capacity of antipeptide Abs, we 1) replaced Gly-40 by an aminoisobutyric moiety (24-41 Aib), 2) substituted the half cystines 24 and 41 by penicillamine moieties (24-41 Pen), and 3) introduced an amide bond between the epsilon NH2 of Lys-27 and the gamma-COOH of Glu-38 (24-41 K-E). A solution ELISA made with antitoxin Abs revealed that 24-41 Pen is more antigenic than 24-41 Aib and 24-41 C, which are more antigenic than 24-41 K-E, suggesting that the conformation of 24-41 Pen is most closely related to the corresponding region in the native toxin.

Pulsed EPR studies of the binuclear Mn(III)Mn(IV) center in catalase from Thermus thermophilus.

The nature of possible protein ligands to the binuclear metal core in manganese catalase from Thermus thermophilus has been addressed by EPR and ESEEM (pulsed EPR) spectroscopies. The three-pulse ESEEM spectrum of the superoxidized Mn(III)Mn(IV) enzyme obtained at 3429 G shows a frequency pattern with peaks at 0.60, 1.

G1 cyclin turnover and nutrient uptake are controlled by a common pathway in yeast.

Entry into a new cell cycle is triggered by environmental signals at a point called Start in G1 phase. A key regulator of this transition step in yeast is the CDC28 kinase together with its short-lived regulatory subunits called G1-cyclins or CLN proteins. To identify genes involved in G1-cyclin degradation, we employed a genetic screen by selecting for stable CLN1-beta-galactosidase fusion proteins.

A second nitrogen permease regulator in Saccharomyces cerevisiae.

We describe a Saccharomyces cerevisiae mutant affected in its urea and proline transport capacities, and a gene coding for a protein complementing this mutation. This protein is not membrane-embedded and contains two PEST sequences, often found in regulatory factors. The mRNA is not down-regulated under nitrogen catabolite repression, and is induced by urea and proline.

Solution structure of an oncogenic DNA duplex, the K-ras gene and the sequence containing a central C.A or A.G mismatch as a function of pH: nuclear magnetic resonance and molecular dynamics studies.

The DNA duplex 5' d(GCCACCAGCTC)-d(GAGCTGGTGGC) corresponds to the sequence 29 to 39 of the K-ras gene, which contains a hot spot for mutations. This has been studied by one and two-dimensional nuclear magnetic resonance, energy minimization and molecular dynamics. The results show that it adopts a globally B-DNA type structure.

[Aggrephores and aquaporins].

The high water permeability of some specialized cells is accounted for by the presence of specific water channels in their plasma membranes. These channels, that play an important role in water homeostasis are now known as aquaporins. Mammalian kidney, in particular contains several forms of aquaporins.

[Functional expression of vasopressin receptors V1a and V2 along the mammalian nephron].

In vitro studies on single microdissected segments have been extensively used during the 20 past years to localize V1 and V2 vasopressin receptors within the mammalian kidney, and define their role in the control of water balance. Based on vasopressin-dependent adenylate cyclase activity measurements and quantitative RT-PCR studies, it is now clear that V2 receptors are present along the whole collecting duct from cortex to papilla, and, in most species, in the ascending limb of Henle's loop (thick and thin limb); occasionally in the distal tubule but not in the other segments. The stimulation by cyclic AMP of sodium chloride reabsorption in the thick ascending limb, and of urea reabsorption in the papillary collecting duct indicates that vasopressin--in addition to its well known hydroosmotic effect--also participates in the building up of the corticopapillary gradient of osmotic pressure.

Effects of brefeldin A on the three-dimensional structure of the Golgi apparatus in a sensitive strain of Saccharomyces cerevisiae.

Background: Brefeldin A (BFA), when added to the medium of cultured mammalian cells, induces a reversible block of secretion and disrupts the Golgi apparatus whereas Golgi enzyme markers appear to redistribute into the endoplasmic reticulum (ER). It has been shown in addition that in mammalian cells, BFA would prevent the assembly of coatomer proteins (COP) onto membranes by inhibiting the GTP-dependent interaction of the ADP-ribosylation factor (ARF) with such membranes. The purpose of the present study is to analyze, by stereoelectron microscopy, the structural modifications of Golgi elements and of the ER-Golgi relationship in a BFA-sensitive yeast mutant, S.

Rapid kinetics of myo-inositol trisphosphate binding and dissociation in cerebellar microsomes.

Using sheep cerebellum microsomes adsorbed on a filter, we measured the kinetics of [3H]inositol 1,4,5-trisphosphate (InsP3) binding and dissociation on the subsecond time scale during rapid perfusion of the filter with [3H]InsP3-containing or InsP3-free media. At 20 degrees C and pH 7.1, in a cytosol-like medium containing MgCl2, the half-time for InsP3 dissociation was as short as 125 ms.

SSS1 encodes a stabilizing component of the Sec61 subcomplex of the yeast protein translocation apparatus.

The yeast SSS1 gene has been isolated as an extragenic high copy suppressor of sec61, a mutant displaying defects in protein translocation into the endoplasmic reticulum (ER). We found that SSS1 is an essential gene required for transfer of secretory precursors through the ER membrane. Here we demonstrate that the SSS1 product (Sss1p) is firmly bound to the ER membrane and exposes its amino-terminal half on the cytosolic side.

A liquid crystalline phase in spermidine-condensed DNA.

Over a large range of salt and spermidine concentrations, short DNA fragments precipitated by spermidine (a polyamine) sediment in a pellet from a dilute isotropic supernatant. We report here that the DNA-condensed phase consists of a cholesteric liquid crystal in equilibrium with a more concentrated phase. These results are discussed according to Flory's theory for the ordering of rigid polymers.

A mutation in the largest subunit of yeast TFIIIC affects tRNA and 5 S RNA synthesis. Identification of two classes of suppressors.

We report the characterization of a mutation affecting tau 138, the largest subunit of yeast transcription factor IIIC (TFIIIC). A previously described thermosensitive mutation (tsv115), tightly linked to the centromere of chromosome I (Harris, S.D.

A diversified family of 12-kDa proteins with a high amino acid sequence similarity to macrophage migration-inhibitory factor (MIF).

Two isoforms of a bovine-brain-derived 12-kDa protein (designated p12a and p12b) whose N-termini have a high amino acid sequence similarity with the glycosylation-inhibiting factor (GIF) and macrophage migration-inhibitory factor (MIF) were purified to homogeneity. The complete amino acid sequence of bovine p12a (pI 9.5) was determined by Edman degradation of the intact molecule and overlapping fragments generated by proteolytic cleavage.

Ultrastructural modifications of vesicular and Golgi elements in the Saccharomyces cerevisiae sec21 mutant at permissive and non-permissive temperatures.

Background: The secretory protein transit between cisternae of endoplasmic reticulum (ER) and Golgi elements is blocked when the yeast Saccharomyces cerevisiae sec21 mutant is shifted from the permissive (24 degrees C) to a non-permissive (37 degrees C) temperature, but 30-50 nm vesicles accumulate in the cytoplasm. At the semi-permissive temperature of 33 degrees C there is no complete block but rather a slowdown of the protein transport between ER and Golgi. The purpose of the present investigation is to analyze the structural expression of these events.

Structure and binding site of the primary electron acceptor in the reaction center of Chlorobium.

In isolated, chlorosome-free reaction centers from Chlorobium limicola f thiosulphatophilum, a chlorin pigment exhibits a Qy absorption band at 672 nm (Feiler, U., Nitschke, W., & Michel, H.

Angular orientation of the stable tyrosyl radical within photosystem II by high-field 245-GHz electron paramagnetic resonance.

The 4 K 245-GHz/8.7-T electron paramagnetic resonance spectrum of the stable tyrosyl radical in photosystem II, known as TyrD., has been measured.

BFR1, a multicopy suppressor of brefeldin A-induced lethality, is implicated in secretion and nuclear segregation in Saccharomyces cerevisiae.

Brefeldin A (BFA) blocks protein transport out of the Golgi apparatus and causes disassembly of this organelle in mammalian cells. The primary effect of BFA is the release of the non-clathrin coat from Golgi membranes and vesicles. We sought to elucidate the mechanism of BFA action using a genetic approach in Saccharomyces cerevisiae.