Human glucokinase gene: isolation, characterization, and identification of two missense mutations linked to early-onset non-insulin-dependent (type 2) diabetes mellitus

DNA polymorphisms in the glucokinase gene have recently been shown to be tightly linked to early-onset non-insulin-dependent diabetes mellitus in approximately 80% of French families with this form of diabetes. We previously identified a nonsense mutation in exon 7 in one of these families and showed that it was the likely cause of glucose intolerance in this dominantly inherited disorder. Here we report the isolation and partial sequence of the human glucokinase gene and the identification of two missense mutations in exon 7, Thr-228----Met and Gly-261----Arg, that cosegregate with early-onset non-insulin-dependent diabetes mellitus. To assess the molecular mechanism by which mutations at these two sites may affect glucokinase activity, the crystal structure of the related yeast hexokinase B was used as a simple model for human beta-cell glucokinase. Computer-assisted modeling suggests that mutation of Thr-228 affects affinity for ATP and mutation of Gly-261 may alter glucose binding. The identification of mutations in glucokinase, a protein that plays an important role in hepatic and beta-cell glucose metabolism, indicates that early-onset non-insulin-dependent diabetes mellitus may be primarily a disorder of carbohydrate metabolism.

Apolipoprotein AI mutation Arg-60 causes autosomal dominant amyloidosis

A mutation in the gene for apolipoprotein AI (apoAI) was identified in an English family with autosomal dominant non-neuropathic systemic amyloidosis. The plasma of all affected individuals contained a variant apoAI with one additional charge, as well as normal apoAI. The propositus was heterozygous; the coding region of his apoAI gene contained both the normal sequence and a single-base substitution changing the codon for residue 60 of the mature protein from CTG (leucine) to CGG (arginine). Allele-specific oligonucleotide hybridization showed that the other affected individuals were also heterozygotes and that there was concordance of the mutant allele with the presence of variant plasma apoAI. Amyloid fibrils isolated from the spleen of the propositus consisted of proteins that ran as a doublet with an apparent mass of approximately 10 kDa in SDS/PAGE and a trace band at 28 kDa. Electrospray mass spectrometry of the purified 10-kDa material revealed components with mass corresponding to the N-terminal 88, 92, 93, and 94 residues of apoAI each with substitution of arginine for leucine. These observations were confirmed by direct protein sequencing and laser desorption time-of-flight mass analysis. No material with the normal apoAI sequence was detected. The trace band at 28 kDa yielded the N-terminal sequence of mature apoAI, indicating that intact or minimally degraded apoAI was also present in the fibril preparation. Discovery of this mutation and the detailed characterization of the apoAI fragments that form the amyloid fibrils open additional avenues for investigation of amyloidogenesis.

Stochastic rearrangement of immunoglobulin variable-region genes in chicken B-cell development

The molecular mechanism by which immunoglobulin (Ig) gene rearrangement occurs is highly conserved between mammalian and avian species. However, in avian species, an equivalent to the mammalian pre-B cell, which has undergone Ig heavy-chain gene rearrangement and expresses mu heavy chains in the absence of Ig light-chain rearrangement, has not been convincingly demonstrated. It is consequently unclear whether an ordered progression of gene rearrangement events leading to functional Ig expression occurs in avian species. To examine the sequence of Ig gene rearrangement events in chicken B-cell development, we transformed day 12 embryo bursal cells with the REV-T(CSV) retrovirus. More than 100 clones were analyzed by Southern blotting and polymerase chain reaction for the presence of Ig gene rearrangements. The majority of these clones contained only germline Ig sequences. Several clones contained complete heavy- and light-chain rearrangements and 13 clones contained only heavy-chain rearrangements analogous to stages of mammalian B-cell development. However, 5 clones contained rearrangements of light-chain genes in the absence of complete heavy-chain rearrangement. Consequently, we conclude that rearrangement of chicken Ig light-chain genes does not require heavy-chain variable-region rearrangement. This observation suggests that chicken Ig gene rearrangement events required for Ig expression occur stochastically rather than sequentially.

Long-term expression of human adenosine deaminase in rhesus monkeys transplanted with retrovirus-infected bone-marrow cells

Gene transfer into hemopoietic stem cells could offer a lasting cure for a variety of congenital disorders. As a preclinical test for such a gene therapy, rhesus monkeys were transplanted with autologous bone-marrow cells infected with helper-free recombinant retroviruses carrying the human adenosine deaminase gene. The in vivo regenerative capacity of the infected bone marrow could be conserved, suggesting survival of repopulating hemopoietic stem cells. In the hemopoietic system of transplanted animals the foreign gene could be observed for as long as the animals were analyzed (in two monkeys greater than 1 yr after transplantation). Genetically modified cell types and tissues included peripheral blood mononuclear cells, granulocytes, bone-marrow cells of various densities, and spleen and lymph nodes. The presence of the provirus in the short-living granulocytes greater than 1 yr after bone-marrow transplantation provided evidence for the transduction of very primitive hemopoietic progenitors. Moreover, the gene transfer resulted in sustained production of functional human adenosine deaminase enzyme in peripheral blood mononuclear cells. These results demonstrate the feasibility of bone-marrow gene-therapy approaches, in particular for treating adenosine deaminase deficiency.

The effects of catalase gene overexpression on life span and resistance to oxidative stress in transgenic Drosophila melanogaster

Oxygen free radicals and hydroperoxides have been postulated to play a causal role in the aging process, implying that antioxidant enzymes may act as longevity determinants. Catalase (H2O2:H2O2 oxidoreductase; EC1.11.1.6) is the sole enzyme involved in the elimination of H2O2 in Drosophila melanogaster; glutathione peroxidase being absent. A genomic fragment containing the Drosophila catalase gene was used to construct transgenic Drosophila lines by means of P element-mediated transformation. Enhanced levels of catalase (up to 80%) did not prolong the life span of flies, nor did they provide improved protection against oxidative stress induced by hyperoxia or paraquat treatment. However, enhanced resistance to hydrogen peroxide was observed in the overexpressors.

Classification and evolution of alpha-amylase genes in plants

The DNA sequences for 17 plant genes for alpha-amylase (EC 3.2.1.1) were analyzed to determine their phylogenetic relationship. A phylogeny for these genes was obtained using two separate approaches, one based on molecular clock assumptions and the other based on a comparison of sequence polymorphisms (i.e., small and localized insertions) in the alpha-amylase genes. These polymorphisms are called "alpha-amylase signatures" because they are diagnostic of the gene subfamily to which a particular alpha-amylase gene belongs. Results indicate that the cereal alpha-amylase genes fall into two major classes: AmyA and AmyB. The AmyA class is subdivided into the Amy1 and Amy2 subfamilies previously used to classify alpha-amylase genes in barley and wheat. The AmyB class includes the Amy3 subfamily to which most of the alpha-amylase genes of rice belong. Using polymerase chain reaction and oligonucleotide primers that flank one of the two signature regions, we show that the AmyA and AmyB gene classes are present in approximately equal amounts in all grass species examined except barley. The AmyB (Amy3 subfamily) genes in the latter case are comparatively underrepresented. Additional evidence suggests that the AmyA genes appeared recently and may be confined to the grass family.

Isolation and sequencing of the cDNA coding for spinach 10-formyltetrahydrofolate synthetase. Comparisons with the yeast, mammalian, and bacterial proteins

The one-carbon metabolism enzymes 10-formyltetrahydrofolate synthetase (EC 6.3.4.3), 5,10-methenyltetrahydrofolate cyclohydrolase (EC 3.5.4.9), and 5,10-methylenetetrahydrofolate dehydrogenase (EC 1.5.1.5) can be found on a single trifunctional protein in the eukaryotes examined. The one exception is in spinach leaves where 10-formyltetrahydrofolate synthetase is monofunctional (Nour, J. M., and Rabinowitz, J. C. (1991) J. Biol. Chem. 266, 18363-18369). In the prokaryotes examined, 10-formyltetrahydrofolate synthetase is either absent or is monofunctional. A cDNA clone encoding spinach leaf 10-formyltetrahydrofolate synthetase was isolated through the use of antibodies to the purified enzyme. This clone had an open reading frame of 1914 base pairs and encoded for a protein containing 636 amino acids with a calculated M(r) of 67,727. The percentage identity between spinach 10-formyltetrahydrofolate synthetase and the synthetase domains in the four trifunctional eukaryotic enzymes and the two monofunctional prokaryotic enzymes that have been cloned and sequenced was: 64.9% human, 63.8% rat, 55.6% yeast cytoplasm, 53.8% yeast mitochondria, 47.8% Clostridium acidi-urici, and 47.9% Clostridium thermoaceticum. Clearly the spinach monofunctional protein had greatest homology with the mammalian proteins. The spinach protein is longer than the two other monofunctional prokaryotic proteins. Possible reasons for this are presented. The codon usage and the putative translation initiation sites are examined and compared with other spinach proteins.

Gastric procathepsin E and progastricsin from guinea pig. Purification, molecular cloning of cDNAs, and characterization of enzymatic properties, with special reference to procathepsin E

Procathepsin E and progastricsin were purified from the gastric mucosa of the guinea pig. They were converted to the active form autocatalytically under acidic conditions. Each active form hydrolyzed protein substrates maximally at around pH 2.5. Pepstatin inhibited cathepsin E very strongly at an equimolar concentration, whereas the inhibition was much weaker for gastricsin. Molecular cloning of the respective cDNAs permitted us to deduce the complete amino acid sequences of their pre-proforms; preprocathepsin E and preprogastricsin consisted of 391 and 394 residues, respectively. Procathepsin E has unique structural and enzymatic features among the aspartic proteinases. Lys at position 37, which is common to various aspartic proteinases and is thought to be important for stabilizing the activation segment, was absent at the corresponding position, as in human procathepsin E. The rate of activation of procathepsin E to cathepsin E is maximal at around pH 4.0. It is very different from the pepsinogens and may be correlated with the absence of Lys37. Native procathepsin E is a dimer, consisting of two monomers covalently bound by a disulfide bridge between 2 Cys37. Interconversion between the dimer and the monomer was reversible and regulated by low concentrations of a reducing reagent. Although the properties of the dimeric and monomeric cathepsins E are quite similar, a marked difference was found between them in terms of their stability in weakly alkaline solution: monomeric cathepsin E was unstable at weakly alkaline pH whereas the dimeric form was stable. The generation of the monomer was thought to be the process leading to inactivation, hence degradation of cathepsin E in vivo.

Chloroplast DNA inversions and the origin of the grass family (Poaceae)

The phylogenetic affinities of the grass family (Poaceae) have long been debated. The chloroplast genomes of at least some grasses have been known to possess three inversions relative to the typical gene arrangement found in most flowering plants. We have surveyed for the presence of these inversions in grasses and other monocots by polymerase chain reaction amplification with primers constructed from sequences flanking the inversion end points. Amplification phenotypes diagnostic for the largest inversion (28 kilobase pairs) were found in genera representing all grass subfamilies, and in the nongrass families Restionaceae, Ecdeiocoleaceae, and Joinvilleaceae, but not in any other monocots--notably, Flagellariaceae, Anarthriaceae, Cyperaceae, or Juncaceae. This finding is consistent with one of the two principal views of grass phylogeny in suggesting that Poaceae and Cyperaceae (sedges) are not closest relatives. A second (approximately 6 kilobases) inversion appears to occur in a subset of the families possessing the 28-kilobase inversion and links Joinvilleaceae and Poaceae, while the smallest inversion appears unique to grasses. These inversions thus provide a nested set of phylogenetic characters, indicating a hierarchy of relationships in the grasses and allies, with Joinvilleaceae identified as the likely sister group to the Poaceae.

HPLC separation of 32P-postlabelled benzo[b]fluoranthene-DNA adducts

Analysis using 32P-postlabelling and a recently developed HPLC method resolved the adduct formed by reaction of the benzo[b]fluoranthene (BbF) anti-bay-region diol-epoxide with DNA from the more polar major adduct produced by the hydrocarbon in three different biological systems. In each case, the adduct formed from the anti-bay-region diol-epoxide constituted only a minor proportion of the total DNA modification. Comparisons of the DNA adducts formed from the hydrocarbon with those formed in microsomal incubations from the putative metabolites BbF-9,10-diol, anti-BbF-9,10-diol-11,12-oxide and the 5,9,10- and 6,9,10-BbF-triols indicate that the predominant pathway for BbF activation in skin probably involves a bay-region triol-epoxide possessing a phenolic OH-group on the peninsula ring.

Genes for bone morphogenetic proteins are differentially transcribed in early amphibian embryos

We have previously demonstrated that activin, a member of the TGF-beta family, has a potent mesoderm-inducing activity in Xenopus embryos. In the course of screening for activin-related genes from Xenopus, we have cloned cDNAs for Xenopus homologue of BMP-2, -4 and -7. Northern blot analysis revealed that these BMP genes are maternally encoded and differentially regulated after fertilization. Alkaline phosphatase-inducing assay using the recombinant BMP proteins has shown that at least BMP-2 and -4 have similar activity to mammalian counterparts.

Molecular cloning and chromosomal mapping of a human protein-tyrosine phosphatase LC-PTP

We isolated cDNA clones encoding a protein-tyrosine phosphatase (PTP) from a human T cell PEER cDNA library. The predicted open reading frame encodes a approximately 40-kDa protein composed of 360 amino acids and has no apparent hydrophobic segments, suggesting that it is a nontransmembrane PTP, which was designated as LC-PTP (leukocyte PTP). Northern blot analysis revealed that the LC-PTP mRNA was preferentially expressed in a variety of hematopoietic cells and the transcriptional sizes were approximately 4.0 kilobases and approximately 2.9 kilobases. Fluorescent in situ hybridization revealed that the human LC-PTP gene is located on the chromosome region 1q32.1, which is known to be a site associated with chromosomal deletion in malignant lymphomas, where candidate tumor suppressor genes might be present.

DNA electrophoresis in microlithographic arrays

We have used optical microlithography to fabricate capped quasi-two-dimensional obstacle courses in SiO2. We report here observations using epifluorescence microscopy of the electrophoresis and length fractionation of large DNA molecules confined in arrays. Simple reptation theory, based on the work of deGennes, predicts that at low electric fields the electrophoretic mobility of a polymer of length L much greater than the persistence length p scales inversely with L (ref. 2). But elongation of the coil in the matrix at sufficiently strong electric fields results in a length-independent electrophoretic mobility. The application of suitably timed pulsed electric fields restores the fractionating power of gels for long molecules but the protocols of pulsed-field electrophoresis are semi-empirical because the complex and ill-understood gel matrix plays a critical role in fractionation. Microlithographically constructed obstacle arrays, with their low dimensionality, small volume and extremely reproducible topography, will make it possible to understand the motion and fractionation of large polymer molecules in complex but well characterized topologies.

The SH2 and SH3 domain-containing protein GRB2 links receptor tyrosine kinases to ras signaling

A cDNA clone encoding a novel, widely expressed protein (called growth factor receptor-bound protein 2 or GRB2) containing one src homology 2 (SH2) domain and two SH3 domains was isolated. Immunoblotting experiments indicate that GRB2 associates with tyrosine-phosphorylated epidermal growth factor receptors (EGFRs) and platelet-derived growth factor receptors (PDGFRs) via its SH2 domain. Interestingly, GRB2 exhibits striking structural and functional homology to the C. elegans protein sem-5. It has been shown that sem-5 and two other genes called let-23 (EGFR like) and let-60 (ras like) lie along the same signal transduction pathway controlling C. elegans vulval induction. To examine whether GRB2 is also a component of ras signaling in mammalian cells, microinjection studies were performed. While injection of GRB2 or H-ras proteins alone into quiescent rat fibroblasts did not have mitogenic effect, microinjection of GRB2 together with H-ras protein stimulated DNA synthesis. These results suggest that GRB2/sem-5 plays a crucial role in a highly conserved mechanism for growth factor control of ras signaling.

Regulated expression of syndecan in vascular smooth muscle cells and cloning of rat syndecan core protein cDNA

cDNA encoding the core protein of rat syndecan was cloned from a neonatal rat aortic cDNA library by polymerase chain reaction amplification. Expression of syndecan mRNA in rat aortic vascular smooth muscle (VSM) cells was demonstrated by reverse transcriptase-linked polymerase chain reaction amplification of syndecan sequences using total RNA from rat aortic VSM cells as templates. Polyclonal antibodies against rat syndecan core protein were produced by immunizing rabbits with a recombinant fusion protein containing a fragment of the extracellular domain. The anti-syndecan antibodies immunoprecipitated a large 35SO4-labeled molecule synthesized by cultured rat aortic VSM cells. The immunoprecipitated molecule was identified as a hybrid proteoglycan, based on results of alkaline, nitrous acid, and chondroitinase ABC digestions. On immunoblots the antibodies recognized a proteoglycan of greater than 200 kDa, with a core protein size after deglycosylation of approximately 50 kDa. The anti-syndecan antibodies stained cultured rat aortic VSM cells as well as tissue sections of neonatal and adult rat aortas in the medial, smooth muscle layer. On Northern blots of RNA isolated from cultured VSM cells, a syndecan cDNA probe hybridized to a major RNA species of 2.6 kilobases. Quantitative Northern blot analysis of total RNA isolated from VSM cells harvested at different cell densities revealed a decrease in syndecan mRNA levels with increased cell density. These results demonstrate the regulated synthesis of syndecan by rat VSM cells.

Myosin light chain-2 luciferase transgenic mice reveal distinct regulatory programs for cardiac and skeletal muscle-specific expression of a single contractile protein gene

To examine the relationship between the cardiac and skeletal muscle gene programs, the current study employs the regulatory (phosphorylatable) myosin light chain (MLC-2) as a model system. Northern blotting, primer extension, and RNase protection studies documented the high level expression of the cardiac MLC-2 mRNA in both mouse cardiac and slow skeletal muscle (soleus). Transgenic mouse lines harboring a 2100- or a 250-base pair rat cardiac MLC-2 promoter/luciferase fusion gene were generated, demonstrating high levels of luciferase activity in cardiac muscle, and only background luminescence in slow skeletal muscle and non-muscle tissues. As assessed by in situ hybridization, immunofluorescence, and luminescence assays of luciferase reporter activity in various regions of the heart, both the endogenous MLC-2 gene and the MLC-2 luciferase fusion gene were expressed exclusively in the ventricular compartment, with expression in the atrium at background levels. Point mutations within the conserved regulatory sites HF-1a and HF-1b significantly cripple ventricular muscle specificity, while mutation of the single E-box site was without effect, suggesting that ventricular muscle-specific expression occurs through an E-box-independent pathway. This study provides direct evidence that the cis regulatory sequences in the cardiac/slow twitch MLC-2 gene which confer cardiac and skeletal muscle-specific expression can be clearly segregated, suggesting that distinct regulatory programs may have evolved to control the tissue-specific expression of this single contractile protein gene in cardiac and skeletal muscle.

Characterization of a gene family encoding abscisic acid- and environmental stress-inducible proteins of alfalfa

The phytohormone abscisic acid (ABA) has been proposed as a common mediator controlling adaptive plant responses to a variety of environmental stresses, including water deficit, salinity, wounding, and low temperature. We have recently isolated three cDNAs, pUM90-1, pUM90-2, and pUM91-4, from a cDNA library of ABA-induced mRNAs of alfalfa. These cDNA clones exhibit a very high degree of sequence homology with one another and sequence similarities with certain regions of several stress- and ABA-inducible genes. The polypeptides encoded by these cDNAs are very rich in glycine (35-40%), histidine (7-15%), asparagine (8-14%), and tyrosine (5-10%) and have no tryptophan and proline. All of the encoded polypeptides contain characteristic tandem repeats comprising glycine residues intercepted with histidine and/or tyrosine. The RNAs corresponding to a representative cDNA, pUM90-1, were induced after treatment of seedlings with low temperature, drought, salt, and wounding stress, but not by heat; the induction was maximal under low temperature treatment. ABA and ABA analog rapidly induced the expression of these genes, whereas gibberellic acid treatment exhibited no induction whatsoever. These genes appear to be specifically induced in the shoot tissues. Analysis of ABA induction of genes corresponding to pUM90-1 in alfalfa seedlings of different age groups demonstrated that these genes were inducible in seedlings/plants of all age groups examined. Taken together these results suggest that these cDNA clones encode a group of proteins that are inducible by ABA and multiple environmental stresses and correspond to a new family of genes of plants, designated as ABA- and environmental stress-inducible genes.

cDNA cloning of a novel human ubiquitin carrier protein. An antigenic domain specifically recognized by endemic pemphigus foliaceus autoantibodies is encoded in a secondary reading frame of this human epidermal transcript

Autoantibodies from a patient suffering from endemic pemphigus foliaceus (EPF), a blistering skin disease, were used to screen a lambda gt11 human keratinocyte cDNA library. One immunoreactive cDNA clone (lambda EPF5) containing a 900-base pair insert was isolated and subjected to further analysis. Eight of 25 EPF sera were shown to react with the EPF5 fusion protein on immunoblots. The EPF5 cDNA insert hybridized with a 1.2-kilobase epidermal RNA transcript on a Northern blot. Sequence analysis revealed that lambda EPF5 contained the complete coding sequence for a 24-kDa polypeptide exhibiting significant sequence homology with a family of enzymes known as ubiquitin carrier proteins, or E2s, which are an essential component of the ubiquitin-protein conjugation system. The homology was particularly high in the core region containing the active site cysteine. The keratinocyte ubiquitin carrier protein expressed in bacteria, and isolated either intact or as a glutathione S-transferase fusion protein, exhibited the ability to form a thiol ester linkage with ubiquitin in a ubiquitin activating enzyme (E1)-dependent manner, a characteristic property of ubiquitin carrier proteins. The E2 enzyme encoded by clone EPF5 is the first member of this protein family to be cloned from an epidermal source. Interestingly, the EPF autoantibody-reactive epitope and the ubiquitin carrier protein were shown to be encoded in two different translational reading frames. The relevance of the cloned EPF epitope in the pathogenesis of this autoimmune disorder remains to be determined.

Inverse modulation of steady-state messenger RNA levels of two non-integrin laminin-binding proteins in human colon carcinoma

BACKGROUND

Interactions between cells and the basement membrane glycoprotein laminin are altered during colon cancer progression. Colon carcinoma and normal mucosa cells express a variety of laminin-binding proteins, including the 67-kd laminin receptor (67 LR) and a 31-kd human laminin-binding protein (HLBP31) homologous to the 31-kd human IgE-binding protein/galactoside-binding lectin.

PURPOSE

To investigate whether various laminin-binding proteins are differentially expressed in human colon carcinoma, we studied messenger RNA (mRNA) levels of the 67 LR and HLBP31 in matched tumor and adjacent normal mucosa samples from a series of 21 patients.

METHODS

Total cellular RNA from tumor and normal mucosa was isolated and analyzed by Northern and slot blot hybridization. In addition, HLBP31 protein levels were assessed by the immunoblot technique. Quantitative laminin affinity chromatography was also used to measure the synthesis of HLBP31 protein in five human cancer cell lines.

RESULTS

The steady-state mRNA level of HLBP31 was downregulated (i.e., decreased) in 18 of 21 human colon carcinomas compared with the level in their corresponding normal colonic mucosa. On average, the level of HLBP31 mRNA was decreased 50% +/- 30% (+/- SD) in the colon cancers. The mean ratio of colon cancer HLBP31 mRNA to adjacent normal mucosa HLBP31 mRNA was twofold lower in primary tumors of patients with metastases (0.3 +/- 0.2 SD) than in primary tumors of patients free of metastatic lesions (0.6 +/- 0.2 SD). The differences between the two groups of patients were statistically significant (P less than .05, Wilcoxon-Mann-Whitney test). We have previously shown that the ratio of colon cancer 67 LR mRNA to corresponding normal mucosa 67 LR mRNA was increased in the same patient population. When the two ratios (ratio of cancer to normal HLBP31 mRNA and ratio of cancer to normal 67 LR mRNA) were compared, HLBP31 mRNA/67 LR mRNA was significantly lower (P less than .05) in primary tumors with metastases (mean +/- SD, 0.3 +/- 0.2) than in primary cancers without metastases (mean +/- SD, 0.7 +/- 0.5). The steady-state level of HLBP31 mRNA was directly correlated with the amount of HLBP31 protein in both colon tissue samples and human cancer cell lines.

CONCLUSION

HLBP31 mRNA expression in colon cancer tissues is modulated inversely to that of 67 LR mRNA expression. The down-regulation of HLBP31 appears to be associated with the metastatic capabilities of colon cancer cells.

IMPLICATIONS

Prospective studies on a large cohort should determine if the systematic detection of HLBP31 and 67 LR protein and/or mRNA can be a valuable adjunct in the prognostic evaluation of primary colon cancers.

Histamine N-methyltransferase from rat kidney. Cloning, nucleotide sequence, and expression in Escherichia coli cells

Complementary DNA clones encoding rat kidney histamine N-methyltransferase have been isolated using synthetic oligonucleotide probes based on partial amino acid sequences of tryptic peptides of the purified enzyme. The 1.3-kilobase cDNA consisted of a 5'-noncoding region of 8 nucleotides, a coding region of 885 nucleotides, and a 3'-noncoding region of 369 nucleotides. The encoded protein of 295 amino acid residues had a calculated molecular weight of 33,940.2. After introduction of a prokaryotic expression vector containing the isolated cDNA, Escherichia coli cells expressed histamine N-methyltransferase activity. The enzyme expressed in these cells was isolated and purified as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, whose mobility was identical to the natural enzyme purified from rat kidney. The recombinant enzyme had Vmax and Km values for both histamine and S-adenosylmethionine identical to those of the natural enzyme. All of the inhibitors of the natural enzyme tested showed similar Ki values on both recombinant and natural enzyme.

Three genes for the human high affinity Fc receptor for IgG (Fc gamma RI) encode four distinct transcription products

Three distinct but closely related classes of receptors that bind the Fc portion of immunoglobulin G (Fc gamma RI, -II, and -III) have been identified in humans. Only Fc gamma RI has high affinity for ligand and has a unique third extracellular domain (EC3). We have characterized three genes for human Fc gamma RI (A, B, and C). Each gene consists of six exons, spans 9.4 kilobase pairs, and localizes to chromosome 1. Although they are remarkably similar, genes B and C are notably different from A; in-frame stop codons are present in the EC3 domain of genes B and C, and deletions occur in a splice donor sequence of gene B. Four distinct Fc gamma RI transcripts were analyzed. One transcript, from gene A, would encode a transmembrane receptor with three external domains. A second transcript, an alternatively spliced product of gene B, would encode a two-external domain transmembrane receptor. Two transcripts, from genes B and C, have stop codons in EC3 and would be predicted to generate secreted receptors.

Molecular cloning and expression of a cDNA encoding endothelial cell nitric oxide synthase

Endothelium-derived relaxing factor (EDRF), identified as nitric oxide (NO), is derived from a guanidino nitrogen of L-arginine via its metabolism by nitric oxide synthase (NOS). Herein, we report the molecular cloning of a cDNA encoding the constitutive calcium-calmodulin (Ca2+/CaM)-regulated nitric oxide synthase (ECNOS). A full-length ECNOS clone was isolated by screening a bovine aortic endothelial cell cDNA library using a fragment of rat brain NOS (bNOS) cDNA. This cDNA has an open reading frame of 3615 nucleotides encoding a 1205-amino acid protein. Membranes prepared from COS cells transfected with the ECNOS cDNA demonstrated NADPH- and Ca2+/CaM- dependent conversion of L-, but not D-, arginine to NO and citrulline that was inhibited by NG-nitro-L-arginine methyl ester. Comparison of the deduced amino acid sequence of ECNOS to the bNOS and macrophage NOS (Mac-NOS) sequences revealed 57 and 50% identity, respectively. In addition, ECNOS contains a unique N-myristylation consensus sequence (not shared by bNOS or Mac-NOS) that may explain its membrane localization.

Regulation of gene expression of rat skeletal muscle/liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Isolation and characterization of a glucocorticoid response element in the first intron of the gene

At least two genes encode isoenzymes of rat 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Alternative splicing of one of these genes generates a skeletal muscle-specific transcript from an upstream promoter and a liver-specific transcript from a downstream promoter. A potent glucocorticoid response element was identified in the first intron of the gene, i.e. between liver exon I and exon II. The element is approximately 3.5 kilobase pairs (kb) downstream of the liver isoenzyme transcription start site and 13 kb upstream of exon II of the gene and confers dexamethasone-sensitive expression of chloramphenicol acetyltransferase (CAT) activity from a heterologous thymidine kinase promoter and from both homologous 5'-flanking regions of the gene. This glucocorticoid response element also exhibits androgen- but not estrogen-sensitive expression of CAT activity in HeLa cells cotransfected with the appropriate receptor expression vector. DNase footprint and sequence analysis revealed that the element is comprised minimally of two adjacent 15-mer glucocorticoid receptor dimer binding sites situated in opposite orientations. Glucocortcoid regulation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression in liver and skeletal muscle is mediated by a single complex glucocorticoid response element located in the first intron of the skeletal muscle/liver gene.

Chromosomal localization and organization of the murine genes encoding the beta subunits (AIC2A and AIC2B) of the interleukin 3, granulocyte/macrophage colony-stimulating factor, and interleukin 5 receptors

Chromosomal genes for two mouse homologous beta subunits (AIC2A and AIC2B) of the interleukin-3, granulocyte/macrophage colony-stimulating factor, and interleukin-5 receptors were characterized. Both AIC2A and AIC2B genes were present on a 250-kilobase MluI restriction fragment and were mapped on murine chromosome 15 (these loci were provisionally designated as Il3rb-1 (AIC2A) and Il3rb-2 (AIC2B)), closely linked to the c-sis locus. Both genes consist of 14 exons and span about 28 kb each. The major transcription initiation sites of both genes were mapped at 194 bp from the initiation codon. These genes are 95% identical up to 700 bp from the transcription initiation sites. Potential recognition sequences for hemopoietic transcription factors including GATA-1 and PU.1 in addition to a TATA-like sequence are present in the 5'-flanking region. A stretch of 20 bp including the initiation site is homologous to the corresponding region of the erythropoietin receptor and the interleukin-7 receptor genes and to the initiator sequence of the adeno-associated virus P5 promoter, suggesting a possible role in transcription initiation. Comparison of the exon/intron boundaries of AIC2A and AIC2B genes with those of other members of the cytokine receptor superfamily reveals a conserved evolutionary structure. Isolation of various forms of AIC2 cDNAs reveals differential splicing of the transcripts.