Organization of Xenopus histone gene variants within clusters and their transcriptional expression

Using previously cloned Xenopus nucleosomal core histone genes as hybridization probes, a genomic DNA library of Xenopus laevis was screened for histone gene clusters. From over 200 histone-gene containing clones identified, 36 were selected as possibly containing H1 histone genes by hybridization to a probe derived from a sea urchin H1 histone gene. These 36 clones were further analyzed by hybrid-selected translation for the definitive presence of H1 histone genes. The genes for three different H1 histone variants were found: H1A , H1B and H1C . Mapping of the histone genes within each clone showed that at least three different gene arrangements can occur within a cluster and that the type of H1 histone variant present in a cluster may be related to the cluster type. S1-mapping experiments indicated that histone genes found in different cluster-types can be expressed in oocytes. Also, the H1 gene found in one cluster-type was expressed in at least three different cell-types: oocytes, gastrula-stage embryos, and erythroblasts.     

Calcium and glucose uptake in rat small intestinal brush-border membrane vesicles. Modulation by exogenous hypercortisolism and 1.25-dihydroxyvitamin D-3

The effect of exogenous hypercortisolism and 1,25-dihydroxyvitamin D-3 on small-intestinal calcium and glucose transport in the rat was studied at the level of brush-border membrane vesicles generated from isolated villous cells by a freeze-thaw procedure. At 5 · 10^?5 M extravesicular calcium, initial uptake rates in vesicles prepared from triamcinolone-treated adult rats were decreased by 30% after 5 days. Since calcium ionophore A23187 virtually abolished the difference in calcium uptake, triamcinolone appeared to affect calcium channel density or activity rather than intravesicular binding capacity. Kinetic analysis showed that a decrease in V_max of a saturable calcium transport system could entirely account for the diminished rate of vesicular calcium uptake. Calcium transport rates could be partially restored by in vivo administration of 1,25-dihydroxyvitamin D-3 at a dosage which did not affect vesicular calcium uptake in control animals. Conversely, sodium-driven glucose accumulation in brush-border vesicles from triamcinolone-treated rats was stimulated by 50–70% after 36 h and appeared insensitive to vitamin D. A specific triamcinolone action on the glucose carrier itself rather than on the driving force of the sodium gradient was indicated by (i) a similar stimulation of glucose transport under equilibrium exchange conditions and (ii) an opposite effect of triamcinolone on sodium-driven alanine transport. The triamcinolone-induced changes in calcium and glucose uptake were not accompanied by a gross alteration of membrane integrity in vitro or by major alterations in vesicular protein composition, intravesicular glucose space and sucrase or alkaline phosphatase activity. The modification of vesicular transport properties is discussed in relation to the vitamin D-antagonized inhibition of intestinal calcium uptake and the stimulation of glucose absorption in response to supraphysiologic amounts of glucocorticoids observed in intact epithelium.     

Anion secretion by the isolated rabbit pancreas

The isolated rabbit pancreas secretes a fluid containing chloride and bicarbonate in about equal concentrations. Replacement of bicarbonate by acetate, phosphate or isethionate, replacement of Na⁺ by Li⁺ and addition of ouabain to the bathing medium of the pancreas inhibit the secretion of fluid, chloride and bicarbonate in a similar fashion and by maximally 100%. Replacement of chloride by isethionate inhibits fluid secretion by maximally 50%, chloride secretion by 90% and bicarbonate secretion by 20%. It is concluded that fluid secretion is based on a Na⁺-gradient-dependent bicarbonate influx or proton efflux in the ductular cell, and that the secretion of chloride is secondary to that of bicarbonate.     

Binding of simple carbohydrates and some N-acetyllactosamine-containing oligosaccharides to Erythrina cristagalli agglutinin as followed with a fluorescent indicator ligand

Erythrina cristagalli agglutinin, a dimeric lectin [J. L. Iglesias, et al. (1982) Eur. J. Biochem.123, 247–252] was shown by equilibrium dialysis to be bivalent for 4-methylumbelliferyl-β-d-galactoside. Upon binding to the lectin, this ligand showed a difference absorption spectrum with two maxima (at 322 and 336 nm) of equal intensity (Δ? = 1.2 × 10³m^?1 cm^?1). A similar spectrum with a comparable value of Δ? was obtained with 4-methylumbelliferyl-N-acetyl-β-d-galactosaminide. Binding of methyl-α-d-galactoside, lactose, and N-acetyllactosamine all produced small but equally intense protein difference spectra with a maximum (Δ? = 2.8 × 10² M^?1 cm^?1) at 291.6 nm. Upon binding of N-dansyl-d-galactosamine to the lectin, there was a fivefold increase in fluorescence intensity of this ligand. The association constant for N-dansyl-d-galactosamine was caused by a very favorable ΔS° of the dansyl group without affecting the strictly carbohydrate-specific character of binding. N-Dansyl-d-galactosamine was employed as a fluorescent indicator ligand in substitution titrations. This involved the use of simple carbohydrates, N-acetyllactosamine, and oligosaccharides which occur in the carbohydrate units of N-glycoproteins; the latter were Gal(β → 4)GlcNAc(β1 → 2)Man, Gal(β1 → 4)GlcNAc(β1 → 6)Man, and Gal(β1 → 4)GlcNAc(β1 → 6)[Gal(β1 → 4)GlcNAc(β1 → 2)]Man. The titrations were performed at two temperatures to determine the thermodynamic parameters. In the series N-acetyl-d-galactosamine, methyl-α-d-galactoside, and lactose, ?ΔH° increased from 24 to 41 kJ mol^?1; it increased further for N-acetyllactosamine and then remained unchanged for the N-acetyllactosamine-containing oligosaccharides (55 ± 1 kJ mol^?1). This indicated that the site specifically accommodated the disaccharide structure with an important contribution of the 2-acetamido group in the penultimate sugar. Beyond this, no additional contacts seemed to be formed. This conclusion also followed from considerations of ΔS° values which became more unfavorable in the above series (?23 to ?101 ± 4 J mol^?1 K^?1); the most negative value of ΔS° was observed with N-acetyllactosamine and the three N-acetyllactosamine-containing oligosaccharides.     

Action of veratridine on acetylcholinesterase in cultures of rat muscle cells

Studies on cultures of embryonic rat muscle cells have suggested that the presence of collagen-tailed forms may be correlated with spontaneous contractile activity: these forms disappear in the presence of tetrodotoxin which blocks the sodium channels involved in the propagation of action potentials. The effect of veratridine, a drug which maintains the sodium channels in the open state, was studied. It is shown here that in young cultures veratridine provoked a dramatic increase in total acetylcholinesterase activity and changed the distribution of the molecular forms of the enzyme, increasing the proportion and absolute amount of the A12 form. In order to elucidate the mechanism of action of this drug, the effects of various ions, ionophores, or other agents that modify the ionic permeabilities of membranes were also investigated.     

The biosynthesis of the ubiquinol-cytochrome c reductase complex in yeast. DNA sequence analysis of the nuclear gene coding for the 14-kDa subunit

The nuclear gene coding for the imported 14-kDa subunit of the ubiquinol-cytochrome c reductase of yeast mitochondria has been sequenced in an attempt to define regulatory and protein topogenic elements. The gene has a length of 381 base pairs and is potentially capable of encoding a polypeptide of 14561 Da. It is transcribed into a single low-abundance RNA of 680 nucleotides whose 5' and 3' termini map, respectively, 30-35 nucleotides upstream and 180-190 nucleotides downstream of the initiator and termination codons. Consistent with the estimated low level of the mRNA, codon usage in the gene is not strongly biased and other features, characteristic of highly expressed genes in yeast, are absent. The 14-kDa protein is predicted to be a predominantly hydrophilic protein, with only a single, short hydrophobic stretch located between positions 19-38. Comparison with other imported mitochondrial proteins so far sequenced has failed to reveal unifying features that might serve as targeting elements. Steady-state levels of the 14-kDa and 11-kDa subunits are reduced in mit- mutants which synthesize truncated forms of apocytochrome b and in these, newly synthesized subunits exhibit a specifically increased turnover rate. We suggest that association of these two subunits with the complex may be mediated or enhanced by interaction with other subunits, in particular cytochrome b.     

Phase behavior of isolated photoreceptor membrane lipids is modulated by bivalent cations

The phase behavior of isolated photoreceptor membrane lipids is further investigated by ³¹P-NMR, in view of earlier discrepant results [(1979) Biochim. Biophys. Acta 558, 330–337; (1982) FEBS Lett. 124, 93–99]. We present evidence that the discrepancy is due to bivalent cations. When resuspended in aqueous media at neutral pH in the absence of bivalent cations, the isolated photoreceptor membrane lipids largely adopt the bilayer configuration. However, upon addition of such cations (Ca²⁺ Mg²⁺) or when resuspended in their presence, the formation of other phases (hexagonal H_II, lipidic particles) results. The rate of this transition depends on cation concentration and temperature. The transition is not easily reversed by addition of EDTA. Implications with regard to photoreceptor membrane structure and function need further study.     

Biomechanical models of the human skull: stability of various segments in three simulations

Three simulations by a computer model of human skull, implemented on finite elements and virtual works principles, were performed by a 15 Kg loading of the structure according rules of mechanical stresses of chewing. First model had all elements in place, second was without vault and third was without orbital walls. Stability of the structure was evaluated in terms of "instability coefficient" as an index of sum of moduli and number of considered nodes such moduli give spatial displacement of nodes after loading and deformation of shell elements. All parts of the structure are involved in ensuring stability so that it decreases as different segments or elements are not considered during simulation. The vault plays a great role in total stability of the model while orbital walls appear as a mechanical link between anterior (frontal) and posterior (occipital) parts of the model.     

An improved medium for the isolation of Cryptococcus neoformans from pigeon droppings

Isolation of Cryptococcus neoformans is enhanced when methyl violet at 2 mg l-1 is added to the usual Guizotia abyssinica medium. In preliminary tests the medium has also proved useful for isolating C. neoformans from other sources.     

Anti-thirst action of propranolol

A reduction of the thirst was observed one hour after intramuscolar injection of 0.3 mg/kg propranolol in the rat; this effect was not observed with higher doses. According to work hypotheses, small doses could act blocking renal beta-adrenergic receptors: the stopped renin emission reduces angiotensin production that is the basic factor of thirst. The AA hypothesize that the lack of the effect in response to higher doses of propranolol can be explained through a different action of this drug which antagonizes the first one.