Proteins of the human placental microvillar cytoskeleton. alpha-Actinin.

The human placental syncytiotrophoblast microvilli are supported by an underlying cytoskeleton consisting mainly of actin microfilaments. The major proteins associated with the actin have Mr values of 105 000, 80 000 and 68 000. The 105 000-Mr protein is recognized by an antibody preparation raised to purified chicken gizzard alpha-actinin. Electron microscopy has shown that the human placental protein has dimensions similar to those reported for muscle alpha-actinin. About half of the placental microvillar alpha-actinin is released from the cytoskeleton in the presence of Ca2+. This effect occurs at concentrations of Ca2+ greater than 0.3 muM and has been used as the basis of a method for the purification of the placental alpha-actinin. This sensitivity to Ca2+ is not affected by trifluoperazine and is therefore likely to be a property of the alpha-actinin as such rather than being mediated via calmodulin.     

Primary structure of a structural protein from the cuticle of the migratory locust, Locusta migratoria.

The complete amino acid sequence of a structural protein isolated from pharate cuticle of the locust Locusta migratoria was determined. The protein has an unusual amino acid composition: 42% of the residues are alanine and only 14 of the 20 common amino acid residues are present. The primary structure consists of regions enriched in particular amino acid residues. The N-terminal region and a region close to the C-terminus are enriched in glycine. The rest of the protein is dominated by alanine, except for two short regions enriched in hydrophilic residues. Almost all the proline residues are situated in the alanine-rich regions in a conserved sequence 'A-A-P-A/V'. An internal duplication has taken place covering most of the protein except for the glycine-rich regions. Owing to the unusual features of the protein a combination of automated Edman degradations and plasma-desorption m.s. was used to determine the complete sequence. The protein does not show sequence homology to other proteins, but proteins divided into regions enriched in the same kind of amino acid residues have been isolated from other insect structures.     

Electron microscopic study of Saccharomyces cerevisiae rDNA chromatin replication.

An electron microscopic study was made of the replication of rDNA chromatin of Saccharomyces cerevisiae. Two different methods were used to synchronize cells. cdc7-1 cells were raised to a restrictive temperature, whereas A364a cells were blocked with mating factor. Replication bubbles typically opened in the nontranscribed spacers of rDNA repeats in both cell types. The mean position of the center of these bubbles corresponds closely to a position where an autonomously replicating sequence previously has been mapped in an rDNA repeat. Clusters of replication bubbles containing up to four bubbles spaced one to three genes apart were seen opening in early S phase.     

Translational regulation of light-induced ribulose 1,5-bisphosphate carboxylase gene expression in amaranth.

The regulation of the genes encoding the large and small subunits of ribulose 1,5-bisphosphate carboxylase was examined in amaranth cotyledons in response to changes in illumination. When dark-grown cotyledons were transferred into light, synthesis of the large- and small-subunit polypeptides was initiated very rapidly, before any increase in the levels of their corresponding mRNAs. Similarly, when light-grown cotyledons were transferred to total darkness, synthesis of the large- and small-subunit proteins was rapidly depressed without changes in mRNA levels for either subunit. In vitro translation or in vivo pulse-chase experiments indicated that these apparent changes in protein synthesis were not due to alterations in the functionality of the mRNAs or to protein turnover, respectively. These results, in combination with our previous studies, suggest that the expression of ribulose 1,5-bisphosphate carboxylase genes can be adjusted rapidly at the translational level and over a longer period through changes in mRNA accumulation.     

Relaxation studies on the interaction of hexamethonium with acetylcholine-receptor channels inAplysia neurons

The mode of action of the cholinergic antagonist hexamethonium on the excitatory responses of voltage-clamped Aplysia neurons to acetylcholine (ACh) has been examined by voltage- and concentration-jump relaxation analysis. At steady-state concentrations of ACh hyperpolarizing command steps induced inward current relaxations to a new steady-state level (Iss). The time constants of these inward relaxations, tau f, which approximate the mean single-channel lifetime, were increased both by increasing the membrane potential and by lowering the bath temperature (Q10 = 3) but were not affected by increasing the ACh concentration over the dose range employed. In the presence of hexamethonium hyperpolarizing command steps produced biphasic relaxations of the agonist-induced current. tau f was reduced in a voltage-dependent manner, the degree of reduction increasing with hyperpolarization. Slow, inverse relaxations were also triggered in the presence of hexamethonium. The time constant of this relaxation was reduced by increasing membrane potential and hexamethonium concentration. Both the estimated association (kf = 5 X 10(4) M-1 . sec-1) and the estimated dissociation (kb = 0.24-0.29 sec-1) rate constants derived from a three-state sequential model for block by hexamethonium were independent of the membrane potential. Similar rate constants were estimated from experiments with the concentration-jump technique, which were also independent of the membrane potential over the range -50 to -110 mV. It is suggested that the voltage-dependent actions of hexamethonium may originate either from an alteration of the channel opening and closing rate constants through an allosteric interaction with the ACh receptor, rather than through an influence of the transmembrane electric field on the rate of drug binding, or through a fast reaction which is rate-limited by voltage-independent diffusion.     

Thermotoga maritima sp. nov. represents a new genus of unique extremely thermophilic eubacteria growing up to 90°C

A novel type of bacterium has been isolated from various geothermally heated locales on the sea floor. The organisms are strictly anaerobic, rod-shaped, fermentative, extremely thermophilic and grow between 55 and 90°C with an optimum of around 80°C. Cells show a unique sheath-like structure and monotrichous flagellation. By 16S rRNA sequencing they clearly belong to the eubacteria, although no close relationship to any known group could be detected. The majority of their lipids appear to be unique in structure among the eubacteria. Isolate MSB8 is described as Thermotoga maritima, representing the new genus Thermotoga.Dedicated to Otto Kandler on the occasion of his 65th birthday Present addresses: University of South Dakota, Vermillion, USA; University of Illinois, Urbana, USA; Universität für Bodenkultur, Wien, Austria     

Pyrococcus furiosus sp. nov. represents a novel genus of marine heterotrophic archaebacteria growing optimally at 100°C

Ten strains representing a novel genus of marine thermophilic archaebacteria growing at between 70 and 103°C with an optimal growth temperature of 100°C and a doubling time of only 37 min were isolated from geothermally heated marine sediments at the beach of Porto di Levante, Vulcano, Italy. The organisms are spherical-shaped, 0.8 to 2.5 m in width and exhibit monopolar polytrichous flagellation. They are strictly anaerobic heterotrophs, growing on starch, maltose, peptone and complex organic substrates. Only CO₂ and H₂ could be detected as metabolic products, the latter being inhibitory to growth at high concentrations. Hydrogen inhibition can be prevented by the addition of S^o, whereupon H₂S is formed in addition, most likely as the result of a detoxification reaction. The GC-content of the DNA of isolate Vc 1 is 38 mol%. The new genus is named Pyrococcus, the fireball. Type species and strain is Pyrococcus furiosus Vc 1 (DSM 3638).     

Characterization of 3''----5'' exonuclease associated with DNA polymerase of silkworm nuclear polyhedrosis virus.

3'----5' Exonuclease specific for single-stranded DNA copurified with DNA polymerase of nuclear polyhedrosis virus of silkworm Bombyx mori (BmNPV Pol). BmNPV Pol has no detectable 5'----3' exonuclease activity on single-stranded or duplex DNA. Analysis of the products of 3'----5' exonucleolytic reaction showed that deoxynucleoside monophosphates were released during the hydrolysis of single-stranded DNA. The exonuclease activity cosedimented with the polymerase activity during ultracentrifugation of BmNPV Pol in glycerol gradient. The polymerase and the exonuclease activities of BmNPV Pol were inactivated by heat with nearly identical kinetics. The mode of the hydrolysis of single-stranded DNA by BmNPV Pol-associated exonuclease was strictly distributive. The enzyme dissociated from single-stranded DNA after the release of a single dNMP and then reassociated with a next polynucleotide being degradated.