Molecular genetic basis of the histo-blood group ABO system

The histo-blood group ABO, the major human alloantigen system, involves three carbohydrate antigens (ABH). A, B and AB individuals express glycosyltransferase activities converting the H antigen into A or B antigens, whereas O(H) individuals lack such activity. Here we present a molecular basis for the ABO genotypes. The A and B genes differ in a few single-base substitutions, changing four amino-acid residues that may cause differences in A and B transferase specificity. A critical single-base deletion was found in the O gene, which results in an entirely different, inactive protein incapable of modifying the H antigen.     

Co-localization of molecules involved in antigen processing and presentation in an early endocytic compartment

The pathways of intracellular traffic involved in antigen processing and presentation have been defined by immunoelectron microscopy. The export pathway for class II histocompatibility molecules and the antigen import pathway meet in a peripheral endocytic compartment having all the molecular machinery believed to be required for antigen processing and presentation, including internalized surface immunoglobulins, proteolytic enzymes and invariant chains. This compartment defines a site where peptides from endocytosed antigen can bind class II molecules en route to the cell surface for presentation to T cells.     

No evidence for illegitimate young in monogamous and polygynous warblers

In animals with internal fertilization, paternity is uncertain. In birds, the occurrence of copulations outside the pair-bond has been documented in a number of species, but the extent to which these result in illegitimate young is largely unknown, and constitutes a major deficiency in our understanding of avian mating systems. The analysis of tandemly repeated sequences (minisatellites), has enhanced our ability to make individual identifications and paternity determinations. Here we describe the use of a bird minisatellite DNA probe in assigning paternity in natural populations of the monogamous willow warbler Phylloscopus trochilus and of the polygynous wood warbler Phylloscopus sibilatrix. In both species this probe detects a multiple locus pattern and a single locus that exhibits a variable number of tandem repeats. Although we observed intrusions by non-resident males into the territories of paired males and extra-pair copulations, no illegitimate offspring were detected among 176 young from 32 families of both species, implying that extra-pair copulations have little or no genetic impact.     

Structure of Arc repressor in solution: evidence for a family of beta-sheet DNA-binding proteins

The Arc repressor, which is involved in the switch between lysis and lysogeny of Salmonella bacteriophage P22, does not belong to any of the known classes of DNA-binding proteins. Mutagenesis studies show that the DNA-binding region is located in the 15 N-terminal amino-acid residues. We have now determined the three-dimensional structure of the Arc dimer from an extensive set of interproton-distance data obtained from 1H NMR spectroscopy. A priori, intra- and inter-monomer nuclear Overhauser effects (NOEs) cannot be distinguished for a symmetric dimer. But by using the homology with the Escherichia coli Met repressor we could interpret the NOEs unambiguously in an iterative structure refinement procedure. The final structure satisfies a large set of NOE constraints (1,352 for the dimer). It shows a strongly intertwined dimer, in which residues 8-14 of different monomers form an antiparallel beta-sheet. A model for the Arc repressor-operator complex can account for all available biochemical and genetic data. In this model two Arc dimers bind with their beta-sheet regions in successive major grooves on one side of the DNA helix, similar to the Met repressor interaction. Thus, Arc and Met repressors are members of the same family of proteins, which contain an antiparallel beta-sheet as the DNA-binding motif.     

Small G proteins are expressed ubiquitously in lymphoid cells and do not correspond to Bcl-2

The bcl-2 gene is consistently associated with t(14; 18) chromosomal translocations observed in a large fraction of human B-cell lymphomas. The t(14; 18) translocation results in deregulated expression of the bcl-2 gene and synthesis of inappropriately high levels of the Bcl-2 protein. Gene transfer studies suggest a role for Bcl-2 in cell survival, growth enhancement and oncogenic transformation. To test the suggestion that GTP-binding by Bcl-2 may mediate its biological effects we characterized the GTP-binding proteins in lymphoid cells expressing Bcl-2. Expression of several small GTP-binding proteins was found to be ubiquitous and did not vary with levels of Bcl-2. By using immunological, electrophoretic and cell-fractionation techniques, we separated Bcl-2 from G proteins of small relative molecular mass (Mr) and showed that it is incapable of binding GTP. Our results show that small Mr G proteins are widely expressed in lymphoid cells and that Bcl-2 is not a novel member of this GTP-binding protein family.     

Voltage-dependent InsP3-insensitive calcium channels in membranes of pancreatic endoplasmic reticulum vesicles.

Stimulus-secretion coupling in exocrine glands involves Ca2+ release from intracellular stores. In endoplasmic reticulum vesicle preparations from rat exocrine pancreas, an inositol 1,4,5-trisphosphate(InsP3)-sensitive, as well as an InsP3-insensitive, Ca2+ pool has been characterized. But Ca2+ channels in the endoplasmic reticulum of rat exocrine pancreas have not been demonstrated at the level of single-channel current. We have now used the patch-clamp technique on endoplasmic reticulum vesicles fused by means of the dehydration-rehydration method. In excised patches, single Ba2(+)- and Ca2(+)-selective channels were recorded. The channel activity was markedly voltage-dependent. Caffeine increased channel open-state probability, whereas ruthenium red and Cd2+ blocked single-channel currents. Ryanodine, nifedipine and heparin had no effect on channel activity. The channel activity was not dependent on the free Ca2+ concentration, the presence of InsP3, or pH. We conclude that this calcium channel mediates Ca2+ release from an intracellular store through an InsP3-insensitive mechanism.     

Expression of cystic fibrosis transmembrane conductance regulator corrects defective chloride channel regulation in cystic fibrosis airway epithelial cells.

The cystic fibrosis transmembrane conductance regulator (CFTR) was expressed in cultured cystic fibrosis airway epithelial cells and Cl- channel activation assessed in single cells using a fluorescence microscopic assay and the patch-clamp technique. Expression of CFTR, but not of a mutant form of CFTR (delta F508), corrected the Cl- channel defect. Correction of the phenotypic defect demonstrates a causal relationship between mutations in the CFTR gene and defective Cl- transport which is the hallmark of the disease.     

Synthetic analogues of fumagillin that inhibit angiogenesis and suppress tumour growth.

Neovascularization is critical for the growth of tumours and is a dominant feature in a variety of angiogenic diseases such as diabetic retinopathy, haemangiomas, arthritis and psoriasis. Recognition of the potential therapeutic benefit of controlling unabated capillary growth has led to a search for safe and effective angiogenesis inhibitors. We report here the synthesis of a family of novel inhibitors that are analogues of fumagillin, a naturally secreted antibiotic of Aspergillus fumigatus fresenius. We first isolated this fungus from a contaminated culture of capillary endothelial cells. Purified fumagillin inhibited endothelial cell proliferation in vitro and tumour-induced angiogenesis in vivo; it also inhibited tumour growth in mice, but prolonged administration was limited because it caused severe weight loss. Synthesis of fumagillin analogues yielded potent angiogenesis inhibitors ('angioinhibins') which suppress the growth of a wide variety of tumours with relatively few side-effects.     

Expression and characterization of the cystic fibrosis transmembrane conductance regulator.

Cystic fibrosis (CF) is a common lethal genetic disease that manifests itself in airway and other epithelial cells as defective chloride ion absorption and secretion, resulting at least in part from a defect in a cyclic AMP-regulated, outwardly-rectifying Cl- channel in the apical surface. The gene responsible for CF has been identified and predicted to encode a membrane protein termed the CF transmembrane conductance regulator (CFTR). Identification of a cryptic bacterial promoter within the CFTR coding sequence led us to construct a complementary DNA in a low-copy-number plasmid, thereby avoiding the deleterious effects of CFTR expression on Escherischia coli. We have used this cDNA to express CFTR in vitro and in vivo. Here we demonstrate that CFTR is a membrane-associated glycoprotein that can be phosporylated in vitro by cAMP-dependent protein kinase. Polyclonal and monoclonal antibodies directed against distinct domains of the protein immunoprecipitated recombinant CFTR as well as the endogenous CFTR in nonrecombinant T84 cells. Partial proteolysis fingerprinting showed that the recombinant and non-recombinant proteins are indistinguishable. These data, which establish several characteristics of the protein responsible for CF, will now enable CFTR function to be studied and will provide a basis for diagnosis and therapy.