A novel product of the Duchenne muscular dystrophy gene which greatly differs from the known isoforms in its structure and tissue distribution.

In Swiss 3T3 cells, depletion of protein kinase C (PKC) by prolonged incubation with phorbol esters potentiates the formation of total inositol phosphates in response to bombesin or vasopressin [Blakeley, Corps & Brown (1989) Biochem. J. 258, 177-185]. The characteristics of the accumulation of inositol phosphates in control and PKC-depleted cells stimulated by bombesin, vasopressin or prostaglandin F2 alpha (PGF2 alpha) have now been compared. The potentiation of the PGF2 alpha response was greater than that of the vasopressin response which was, in turn, greater than that of the bombesin response. The time courses of the responses to all three agonists were biphasic, and both phases of the response were amplified in the PKC-depleted cells. These results provide further evidence for the involvement of a PKC-mediated negative-feedback loop regulating phosphoinositide hydrolysis in response to several 3T3 cell mitogens. The differential potentiation of the response to these agonists suggests that PKC might act at multiple sites within the signal transduction pathway.     

Prebiotic synthesis of diaminopyrimidine and thiocytosine

The reaction of guanidine hydrochloride with cyanoacetaldehyde gives high yields (40–85%) of 2,4-diaminopyrimidine under the concentrated conditions of a drying lagoon model of prebiotic synthesis, in contrast to the low yields previously obtained under more dilute conditions. The prebiotic source of cyanoacetaldehyde, cyanoacetylene, is produced from electric discharges under reducing conditions. The effect of pH and concentration of guanidine hydrochloride on the rate of synthesis and yield of diaminopyrimidine were investigated, as well as the hydrolysis of diaminopyrimidine to cytosine, isocytosine, and uracil. Thiourea also reacts with cyanoacetaldehyde to give 2-thiocytosine, but the pyrimidine yields are much lower than with guanidine hydrochloride or urea. Thiocytosine hydrolyzes to thiouracil and cytosine and then to uracil. This synthesis would have been a significant prebiotic source of 2-thiopyrimidines and 5-substituted derivatives of thiouracil, many of which occur in tRNA. The applicability of these results to the drying lagoon model of prebiotic synthesis was tested by dry-down experiments where dilute solutions of cyanoacetaldehyde, guanidine hydrochloride, and 0.5m NaCl were evaporated over varying periods of time. The yields of diaminopyrimidine varied from 1 to 7%. These results show that drying lagoons and beaches may have been major sites of prebiotic syntheses.     

The envelope gp120 gene of human immunodeficiency virus type 1 determines the rate of CD4-positive T-cell depletion in SCID mice engrafted with human peripheral blood leukocytes.

We have used envelope recombinant viruses generated between two molecular clones of human immunodeficiency virus type 1 (HIV-1), T-cell-tropic HIV-1SF2 and macrophage-tropic HIV-1SF162, to assess pathogenic potential in the human peripheral blood leukocyte-reconstituted severe combined immune deficiency mouse model. Recombinant HIV-1SF2 viruses expressing the envelope gp120 gene of HIV-ISF162 caused as rapid a CD4+ T-cell depletion as did HIV-1SF162. The reciprocal HIV-1SF162 recombinant virus with the HIV-1SF2 envelope caused slower CD4+ T-cell loss. Although changing the V3 loop sequence of HIV-1SF162 to that of HIV-1SF2 did not change the rate of CD4+ T-cell depletion, replacing the V3 of HIV-1SF2 with the sequence of HIV-1SF162 resulted in virus that was poorly infectious in vivo but not in vitro. These studies suggest that the envelope gene determines properties important for pathogenesis in vivo as well as for cell tropism in vitro. HIV-1 infection in vivo may have more stringent requirements for envelope conformation.     

Intrinsic pKas of ionizable residues in proteins: An explicit solvent calculation for lysozyme

Molecular dynamics simulations of triclinic hen egg white lysozyme in aqueous solution were performed to calculate the intrinsic pK_as of 14 ionizable residues. An all-atom model was used for both solvent and solute, and a single 180 ps simulation in conjunction with a Gaussian fluctuation analysis method was used. An advantage of the Gaussian fluctuation method is that it only requires a single simulation of the system in a reference state to calculate all the pK_as in the protein, in contrast to multiple simulations for the free energy perturbation method. pK_int shifts with respect to reference titratable residues were evaluated and compared to results obtained using a finite difference Poisson-Boltzmann (FDPB) method with a continuum solvent model; overall agreement with the direction of the shifts was generally observed, though the magnitude of the shifts was typically larger with the explicit solvent model. The contribution of the first solvation shell to the total charging free energies of the titratable groups was explicitly evaluated and found to be significant. Dielectric shielding between pairs of titratable groups was examined and found to be smaller than expected. The effect of the approximations used to treat the long-range interactions on the pK_int shifts is discussed. © 1994 Wiley-Liss, Inc.     

Seasonal growth activity of local and foreign gracilarioid strains in Israel

Six gracilarioid strains originating from different climatical environments were cultured in two cultivation systems: a short-term indoor one with a cross gradiant table, and a long-term outdoor one. Seasonal growth performances of the different strains were determined. The growth results in the two culture systems showed similar trends. The tropical species.Gracilaria cornea andG. cornea mutant, showed highest growth rates during summer and no growth at all during winter. The temperate species,Gracilaria verrucosa andGracilariopsis lemaneiformis, showed best growth performances during winter with small fluctuations between seasons. The subtropical speciesGracilaria conferta (local) showed seasonal growth fluctuations all over the year. The foreign species definitely did not acclimate under local conditions, but successfully preserved their original response to temperature. Regression equations confirmed that temperature was the dominant environmental variable in most of the gracilarioid strains. The growth rate results obtained showed encouraging prospects for high algal productivity as compared to other cultivation systems. Seasonal cultivation strategy ofGracilaria spp. in Israel is discussed.     

Electron microscope tomography of Balbiani Ring hnRNP substructure

Three-dimensional (3-D) reconstructions, by electron microscope tomography, of selectively stained, contrast enhanced Balbiani Ring (BR) hnRNP granules reveal a complex spatial arrangement of RNA-rich domains. This particulate substructure was examined by volume rendering computer graphics. Modeling the arrangement of RNA-rich domains is made difficult by apparent structural flexibility and/or heterogeneity of composition. Formulation of a consensus 3-D arrangement of RNA-rich domains will require an expanded data base of reconstructed BR granules and the development of new image manipulation and analysis techniques. This study demonstrates the potential for ultra-structural cell biology of combining several new techniques: selective nucleic acid staining, electron spectroscopic imaging to enhance contrast, electron microscope tomography and volume rendering computer graphics.Abbreviations BR Balbiani Ring - EMT electron microscope tomography - ESI electron spectroscopic imaging - hnRNP heterogeneous nuclear ribonucleoprotein - OA-B osmium ammine-B - kb kilobases by P.B. Moens     

The dynamics of sparse random networks

Recurrent neural networks with full symmetric connectivity have been extensively studied as associative memories and pattern recognition devices. However, there is considerable evidence that sparse, asymmetrically connected, mainly excitatory networks with broadly directed inhibition are more consistent with biological reality. In this paper, we use the technique of return maps to study the dynamics of random networks with sparse, asymmetric connectivity and nonspecific inhibition. These networks show three qualitatively different kinds of behavior: fixed points, cycles of low period, and extremely long cycles verging on aperiodicity. Using statistical arguments, we relate these behaviors to network parameters and present empirical evidence for the accuracy of this statistical model. The model, in turn, leads to methods for controlling the level of activity in networks. Studying random, untrained networks provides an understanding of the intrinsic dynamics of these systems. Such dynamics could provide a substrate for the much more complex behavior shown when synaptic modification is allowed.     

Cloning and comparative mapping of a gene from the commonly deleted region of DiGeorge and Velocardiofacial syndromes conserved in C. elegans

We have identified and cloned a gene, ES2, encoding a putative 476 amino acid protein with a predicted M _r of 52,568. The gene is localized within the DiGeorge/Velocardiofacial syndrome locus on 22q11.2 and is deleted in all the patients in which a deletion within 22q11 could be demonstrated, with the exception of one patient. ES2 is expressed in all the tissues studied. Sequence comparison showed identity with five ESTs and at the amino acid level the sequence was highly similar to, and collinear with, a hypothetical C. elegans protein of unknown function. Mutation analysis was performed in 16 patients without deletion, but no mutation has been found. The cDNA sequence is conserved in mouse and is localized on MMU16B1-B3, known to contain a syntenic group in common with HSA 22q11.2. Received: 25 March 1996 / Accepted: 15 May 1996