Construction and characterization of two infectious molecular clones of encephalomyocarditis virus.

We constructed and characterized two infectious molecular clones of encephalomyocarditis (EMC) virus. Both constructs, pDL and pDA, were assembled from five overlapping cDNA clones derived from the diabetogenic variant of EMC virus (EMC-D) and from two synthetic oligonucleotide cartridges. pDA contained a single point mutation at position 1720 within the "puff" region of capsid protein 1AB that was derived from the nondiabetogenic variant of EMC virus (EMC-B). This point mutation resulted in an amino acid substitution of arginine (EMC-B) for lysine (EMC-D). Our construction illustrates two novel findings: (i) that the problem of stably cloning long poly(C) tracts of EMC virus can be circumvented by the use of a shortened, synthetic, poly(dC-dG) oligonucleotide cartridge, and (ii) that a single point mutation in the puff region of the capsid protein 1AB leads to change in its electrophoretic mobility and to a change in the plaque size of recombinant virus.     

Ion flow in the bath and flux interactions between channels.

We present an exact solution to the linearized Nernst-Planck-Poisson equation for spherically symmetric current flow. This solution differs from Levitt's solution (Levitt, D. G. 1992. Biophys. J., Eq. A5) by its dependence on an additional parameter, which is equal to the net ion flux for monovalent ion-selective channels. For ion-selective channels, this solution may provide better boundary conditions to modelling the flow in the channel pore itself, although only at low salt concentrations. We use the solution to estimate the effects of flux interaction between closely packed channels.     

Leaf dynamics and standing stocks of intertidal Zostera noltii Hornem. and Cymodocea nodosa (Ucria) Ascherson on the Banc d'Arguin (Mauritania)

Leaf dynamics and standing stocks of intertidal seagrasses were studied in the Baie d'Aouatif (Parc National du Banc d'Arguin, Mauritania) in April and September 1988. Standing stocks of Zostera noltii Hornem. suggest a unimodal seasonal curve similar to what is found for populations at higher latitudes. Also, leaf growth rates (0.03 cm² cm^–2 day^–1 on average) were similar to those found at higher latitudes in these months. Variation in leaf loss over tidal depth, time and different locations in the Baie d'Aouatif was larger and more often significant than variation in leaf growth. In general, Z. noltii beds in the Baie d'Aouatif had comparable leaf growth rates and standing stocks. In both months losses were almost always higher than or equal to growth.Variation in leaf loss over time was much higher in the plots that were situated high in the intertidal than in lower plots. This is explained by differences in susceptibility to sloughing, which is presumably higher in periods with low tide around noon for shallow depths.In an experiment using artificial shading nets, in situ leaf growth was affected negatively from 94% shading onwards. This shading was observed to reduce the light intensity reaching the seagrass bed to a level below the reported range of light compensation points for Z. noltii. Cymodocea nodosa (Ucria) Ascherson on average had higher leaf area and relative growth rates than Z. noltii and much lower loss rates, resulting in a positive net increase in September. Standing stocks were also higher than for Z. noltii. A mixed seagrass bed containing the above two species and Halodule wrightii Ascherson had the highest observed total biomass: 335 g m^–2 ash-free dry weight.     

The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum

Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.     

Population,formal genetics,and linkage relations of the phosphoglycolate phosphatase (PGP)—E.C.3.1.3.18

Summary One hundred and sixty-seven blood donors, 26 families with 72 offspring and 12 motherchild couples were studied for the phosphoglycolate phosphatase polymorphism. In hemolysates, the isozymes are stable for at least five weeks. The distribution of observed phenotypes in the population study did pot diverge from the expected values according to Hardy-Weinberg law. In the family study, the formal genetic model of three alleles—PGP ¹, PGP ² and PGP ³ at one autosomal locus-could be confirmed. Among 33 individuals from a Mongoloid population PGP 1 was observed in 100%. This observation lead us to the conclusion, based also on recent data in Negroid populations (Barker and Hopkinson 1978), that phosphoglycolate phosphatase may be a more recent polymorphism of Caucasoid populations. Linkage studies with the hp locus an chromosome 16 resulted in 19 meiotic divisions of 4 informative families in a lod score peak of 0.23 at =0.25 being inconclusive. The inclusion of the PGP system in paternity testing is also discussed.