AdaptivSearch: A Novel Iterative Algorithm for the Generation of n-dimensional Hypersurfaces Using an Adaptive Numerical Strategy

AdaptivSearch is the first adaptive strategy based algorithm for the rational and economical construction of n-dimensional hypersurfaces. AdaptivSearch works iteratively: At each step it parcels out the definition range into several triangles, evaluates the worst according to a built-in error criterion, and refines the approximation to the unknown function by choosing the barycenter of this partial area as the node to be calculated next. Based upon the error criterion, AdaptivSearch selectively approaches those parts of the hypersurface in which the curvature exhibits the strongest changes. Some examples of AdaptivSearch applications for both analytical functions and chemical model surfaces are given in order to demonstrate the behavior of the algorithm. These show its broad applicability and the usefulness, especially for chemical problems.     

A mutant cysteinyl-tRNA synthetase affecting timing of chromosomal replication initiation in B. subtilis and conferring resistance to a protein kinase C inhibitor.

A Bacillus subtilis mutant spnA95 was isolated as resistant at 30 degrees C to the protein kinase C (PKC) inhibitor, sphinganine, and temperature sensitive for growth. As deduced by flow cytometry measurements, the mutant has a 35% reduced initiation mass at permissive temperature, resulting in initiation of DNA replication much earlier in the cell cycle than in the wild type. This modification is accompanied by a change in cell size, as determined by phase-contrast microscopy and flow cytometry. Therefore, this strain displays the characteristics of a novel cell clock mutant. spnA is a newly identified gene in B.subtilis and was shown to encode a cysteinyl-tRNA synthetase. At non-permissive temperature, the mutant was defective in the synthesis of P70, a protein with several characteristics of PKC (a cysteine-rich protein). As one possibility, we propose that the altered timing of replication may be due to the reduced synthesis of specific cysteine-rich proteins normally involved in controlling chromosomal replication initiation in B. subtilis.     

Succinate-ethanol fermentation in Clostridium kluyveri: purification and characterisation of 4-hydroxybutyryl-CoA dehydratase/vinylacetyl-CoA Δ3-Δ2-isomerase

Anaerobically prepared cell extracts of Clostridium kluyveri grown on succinate plus ethanol contained high amounts of 4-hydroxybutyryl-CoA dehydratase, which catalyzes the reversible dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA. The enzyme was purified 12-fold under strictly anaerobic conditions to over 95% homogeneity and had a specific activity of 123 nkat mg^-1. The finding of this dehydratase means that all of the enzymes necessary for fermentation of succinate plus ethanol by C. kluyveri have now been demonstrated to exist in this organism and confirms the proposed pathway involving a reduction of succinate via 4-hydroxybutyrate to butyrate. Interestingly, the enzyme is almost identical to the previously isolated 4-hydroxybutyryl-CoA dehydratase from Clostridium aminobutyricum. The dehydratase was revealed as being a homotetramer (m=59 kDa/subunit), containing 2±0.2 mol FAD, 13.6±0.8 mol Fe and 10.8±1.2 mol inorganic sulfur. The enzyme was irreversibly inactivated after exposure to air. Reduction by sodium dithionite also yielded an inactive enzyme which could be reactivated, however, up to 84% by oxidation with potassium hexacyanoferrate(III). The enzyme possesses an intrinsic vinylacetyl-CoA isomerase activity which was also found in 4-hydroxybutyryl-CoA dehydratase from C. aminobutyricum. Moreover, the N-terminal sequences of the dehydratases from both organisms were found to be 63% identical.     

Attempts to define functional domains of gap junction proteins with synthetic peptides.

To map the binding sites involved in channel formation, synthetic peptides representing sequences of connexin 32 were tested for their ability to inhibit cell-cell channel formation. Both large peptides representing most of the two presumed extracellular loops of connexin32 and shorter peptides representing subsets of these larger peptides were found to inhibit cell-cell channel formation. The properties of the peptide inhibition suggested that the binding site is complex, involving several segments of both extracellular loops. One of the peptides (a 12-mer) did not inhibit but instead was found to form channels in membranes. Both in oocyte membranes and in bilayers, the channels formed by the peptide were asymmetrically voltage dependent. Their unit conductances ranged from 20 to 160 pS. These data are discussed in the form of a model in which the connexin sequence represented by the peptide is part of a beta structure providing the lining of the channel pore.     

Early helper T-cell dysfunction in simian immunodeficiency virus but not in human immunodeficiency virus type-2-infected macaques

Both naive and vaccinated macaques acquired a virus-specific proliferative helper T-cell reactivity in response to infection with the nonpathogenic human immunodeficiency virus type 2 (HIV-2). In contrast, macaques infected with the pathogenic simian immunodeficiency virus of the macaque strain (SIV_mac) did not develop a helper T-cell response. Furthermore, a vaccine-induced preexisting T-cell reactivity was abrogated after SIV_mac infection in vaccine failures. These differences may reflect the different pathogenicity of the two closely related viruses.     

BrdU incorporation reveals DNA replication in non dividing glial cells in the larval abdominal CNS ofDrosophila

Glial cells are of significant importance for central nervous system development and function. In insects, knowledge of the types and development of CNS glia is rather low. This is especially true for postembryonic glial development. Using bromodeoxyuridine incorporation and enhancer trap lines we identified a reproducible spatial and temporal pattern of DNA replicating cells in the abdominal larval CNS (A3-7 neuromeres) ofDrosophila melanogaster. These cells correspond to embryonically established glial cells in that region. Except for a specific subfraction, these cells apparently do not divide during larval life. Similar patterns were found in two otherDrosophila species,D. virilis andD. hydei.     

Cell surface adhesion receptors

Several new structural motifs found in cell surface adhesion receptors have been described in the past few years. Also, several two-domain structures of extracellular portions of cell surface proteins have been reported. Structural models for complexes between receptors and counter-receptors have been proposed. The first reports on carbohydrate conformation in intact glycoprotein domains have recently appeared. These new data are presented within a more general review of the field of cell adhesion receptors.