DOS, a novel pleckstrin homology domain-containing protein required for signal transduction between sevenless and Ras1 in Drosophila

The specification of the R7 photoreceptor cell in the developing eye of Drosophila is dependent upon activation of the Sevenless (SEV) receptor tyrosine kinase. By screening for mutations that suppress signaling via a constitutively activated SEV protein, we have identified a novel gene, daughter of sevenless (dos). DOS is required not only for signal transduction via SEV but also in other receptor tyrosine kinase signaling pathways throughout development. The presence of an amino-terminally located pleckstrin homology domain and many potential tyrosine phosphorylation sites suggests that DOS functions as an adaptor protein able to interact with multiple signaling molecules. Our genetic analysis demonstrates that DOS functions upstream of Ras1 and defines a signaling pathway that is independent of direct binding of the DRK SH2/SH3 adaptor protein to the SEV receptor tyrosine kinase.

Daughter of sevenless is a substrate of the phosphotyrosine phosphatase Corkscrew and functions during sevenless signaling

The SH2 domain-containing phosphotyrosine phosphatase Corkscrew (CSW) is an essential component of the signaling pathway initiated by the activation of the sevenless receptor tyrosine kinase (SEV) during Drosophila eye development. We have used genetic and biochemical approaches to identify a substrate for CSW. Expression of a catalytically inactive CSW was used to trap CSW in a complex with a 115 kDa tyrosine-phosphorylated substrate. This substrate was purified and identified as the product of the daughter of sevenless (dos) gene. Mutations of dos were identified in a screen for dominant mutations which enhance the phenotype caused by overexpression of inactive CSW during photoreceptor development. Analysis of dos mutations indicates that DOS is a positive component of the SEV signaling pathway and suggests that DOS dephosphorylation by CSW may be a key event during signaling by SEV.

Suppression of proinflammatory cytokines in monocytes by a tetravalent guanylhydrazone

An overproduction of proinflammatory cytokines by activated macrophages/monocytes mediates the injurious sequelae of inflammation, septic shock, tissue injury, and cachexia. We recently synthesized a tetravalent guanylhydrazone compound (CNI-1493) that inhibits cytokine-inducible arginine transport and nitric oxide (NO) production in macrophages, and protects mice against lethal endotoxemia and carrageenan-induced inflammation. During these investigations we noticed that CNI-1493 effectively prevented lipopolysaccharide (LPS)-induced NO production, even when added in concentrations 10-fold less than required to competitively inhibit L-arginine uptake, suggesting that the suppressive effects of this guanylhydrazone compound might extend to other LPS-induced responses. Here, we report that CNI-1493 suppressed the LPS-stimulated production of proinflammatory cytokines (tumor necrosis factor [TNF], interleukins 1beta and 6, macrophage inflammatory proteins 1alpha and 1beta) from human peripheral blood mononuclear cells. Cytokine suppression was specific, in that CNI-1493 did not inhibit either the constitutive synthesis of transforming growth factor beta or the upregulation of major histocompatibility complex class II by interferon gamma (IFN-gamma). In contrast to the macrophage suppressive actions of dexamethasone, which are overridden in the presence of IFN-gamma, CNI-1493 retained its suppressive effects even in the presence of IFN-gamma. The mechanism of cytokine-suppressive action by CNI-1493 was independent of extracellular L-arginine content and NO production and is not restricted to induction by LPS. As a selective inhibitor of macrophage activation that prevents TNF production, this tetravalent guanylhydrazone could be useful in the development of cytokine-suppressive agents for the treatment of diseases mediated by overproduction of cytokines.

Human immunodeficiency virus type 1 infection alters chemokine beta peptide expression in human monocytes: implications for recruitment of leukocytes into brain and lymph nodes

Two chemokine (chemoattractant cytokines) beta peptides, macrophage inflammatory proteins 1 alpha and 1 beta (MIP-1 alpha and MIP-1 beta), were induced in human monocyte cultures following infection with the human immunodeficiency virus type 1 (HIV-1). Induction depended on productive viral infection: not only did the kinetics of MIP-1 peptide induction closely follow those of viral replication, but monocyte cultures inoculated with heat-inactivated virus or infected in the presence of AZT failed to produce these chemokine beta peptides. In addition, HIV infection markedly altered the pattern of beta chemokine expression elicited by tumor necrosis factor (TNF), itself a potent proinflammatory cytokine upregulated during the development of AIDS. Reverse transcription (RT)-PCR and RT-in situ PCR studies on brain tissue from patients with AIDS dementia demonstrated elevated MIP-1 alpha and MIP-1 beta mRNA expression relative to comparable samples from HIV-1-infected patients without dementia. Cells expressing chemokines in HIV-1-infected brains were identified morphologically as microglia and astrocytes. As MIP-1 alpha and MIP-1 beta are potent chemoattractants for both monocytes and specific subpopulations of lymphocytes, this dysregulation of beta chemokine expression may influence the trafficking of leukocytes during HIV infection. These data, taken together, suggest a mechanism by which HIV-1-infected monocytes might recruit uninfected T cells and monocytes to sites of active viral replication or inflammation, notably the brain and lymph nodes.

Detection of human coronavirus 229E-specific antibodies using recombinant fusion proteins

Human coronaviruses are known to be a common cause of respiratory infections in man. However, the diagnosis of human coronavirus infections is not carried out routinely, primarily because the isolation and propagation of these viruses in tissue culture is difficult and time consuming. The aim of this study was to evaluate the use of recombinant, bacterial expressed proteins in the serodiagnosis of coronavirus infections. Two proteins were examined: the human coronavirus 229E nucleocapsid protein (N), expressed as a fusion protein in the vector pUR and the coronavirus 229E surface glycoprotein (S), expressed as a fusion protein in the vector pROS. The recombinant proteins were used as antigens in Western blot (WB) assays to detect the 229E-specific IgG antibodies and the results were compared with a standard serological method, indirect immunofluorescence. Serum samples of 51 paediatric patients, suffering from acute respiratory illness, and 10 adults, voluntarily infected with human coronavirus, were tested. The serum samples of the adult group had coronavirus-specific IgG antibodies in both test systems. In contrast, only 8/51 sera of the paediatric group were positive for coronavirus-specific IgG by both WB and IF and 20/51 sera were positive by WB, but not by IF. The overall incidence of human coronavirus infections in the paediatric age group was 55% evaluated by WB analysis and 16% evaluated by IF. This study shows that recombinant human coronavirus 229E proteins are suitable reagents for the epidemiological screening of coronavirus 229E infections.

Biochemical and genetic analysis of the Drk SH2/SH3 adaptor protein of Drosophila

The Drk SH3-SH2-SH3 adaptor protein has been genetically identified in a screen for rate-limiting components acting downstream of the Sevenless (Sev) receptor tyrosine kinase in the developing eye of Drosophila. It provides a link between the activated Sev receptor and Sos, a guanine nucleotide release factor that activates Ras1. We have used a combined biochemical and genetic approach to study the interactions between Sev, Drk and Sos. We show that Tyr2546 in the cytoplasmic tail of Sev is required for Drk binding, probably because it provides a recognition site for the Drk SH2 domain. Interestingly, a mutation at this site does not completely block Sev function in vivo. This may suggest that Sev can signal in a Drk-independent, parallel pathway or that Drk can also bind to an intermediate docking protein. Analysis of the Drk-Sos interaction has identified a high affinity binding site for Drk SH3 domains in the Sos tail. We show that the N-terminal Drk SH3 domain is primarily responsible for binding to the tail of Sos in vitro, and for signalling to Ras in vivo.

Poly(A) polymerase contains multiple functional domains

Poly(A) polymerase (PAP) contains regions of similarity with several known protein domains. Through site-directed mutagenesis, we provide evidence that PAP contains a functional ribonucleoprotein-type RNA binding domain (RBD) that is responsible for primer binding, making it the only known polymerase to contain such a domain. The RBD is adjacent to, and probably overlaps with, an apparent catalytic region responsible for polymerization. Despite the presence of sequence similarities, this catalytic domain appears to be distinct from the conserved polymerase module found in a large number of RNA-dependent polymerases. PAP contains two nuclear localization signals (NLSs) in its C terminus, each by itself similar to the consensus bipartite NLS found in many nuclear proteins. Mutagenesis experiments indicate that both signals, which are separated by nearly 140 residues, play important roles in directing PAP exclusively to the nucleus. Surprisingly, basic amino acids in the N-terminal-most NLS are also essential for AAUAAA-dependent polyadenylation but not for nonspecific poly(A) synthesis, suggesting that this region of PAP is involved in interactions both with nuclear targeting proteins and with nuclear polyadenylation factors. The serine/threonine-rich C terminus is multiply phosphorylated, including at sites affected by mutations in either NLS.

Genetic dissection of signal transduction mediated by the sevenless receptor tyrosine kinase in Drosophila

The specification of the R7 photoreceptor cell fate in the developing eye of Drosophila depends on the local activation of the sevenless (sev) receptor tyrosine kinase by boss, a protein expressed on the membrane of the neighboring R8 cell. Constitutive activation of the sev receptor results in a dosage dependent increase in the number of R7 cells per ommatidium. Genetic screens have been used to identify mutations that alter the efficiency of signal transduction. Subsequent molecular characterization of the corresponding genes has led to the identification of a number of proteins involved in transducing the signal from the receptor to the nucleus. In contrast to the receptor and its ligand, these components are shared between different signal transduction pathways not only in Drosophila but are also homologous to components involved in signal transduction in other organisms.

Characterization of the human coronavirus 229E (HCV 229E) gene 1

The sequence of the HCV 229E gene 1 has been determined and compared with the homologous sequences of the murine hepatitis virus and the avian infectious bronchitis virus. The coding sequence of gene 1 is 20,273 nucleotides in length. Within this coding region are two large open reading frames, ORF 1a (4,086 codons) and ORF 1b (2,687 codons) which overlap by 40 nucleotides. In the overlapping region, the genomic RNA can be folded into a pseudoknot structure, an element which is known to mediate -1 ribosomal frame-shifting in other coronaviruses. Assuming that -1 frame-shifting occurs at the HCV sequence UUUAAAC (nucleotides 12,514-12,520), the ORF 1a - ORF 1b product is predicted to be 6,758 amino acids in length. Our sequence analysis of the HCV 229E gene 1 has revealed a high degree of similarity within the ORF 1b of HCV, MHV and IBV, whereas ORF 1a is much less conserved. Elements which are believed to be necessary for specific (e.g. frame-shifting) and general (e.g. NTP-binding/helicase) transcriptional functions have been identified. This study completes the genomic sequence of HCV 229E which is 27.27 kb long and one of the largest known RNA genomes.

Nucleotide sequence of the human coronavirus 229E RNA polymerase locus

The nucleotide sequence of the human coronavirus 229E (HCV 229E) RNA polymerase gene and the 5' region of the genome has been determined. The polymerase gene is comprised of two large open reading frames, ORF1a and ORF1b, that contain 4086 and 2687 codons, respectively. ORF1b overlaps ORF1a by 43 bases in the (-1) reading frame. The in vitro translation of SP6 transcripts which include HCV 229E sequences encompassing the ORF1a/ORF1b junction show that expression of ORF1b can be mediated by ribosomal frame-shifting. The predicted translation products of ORF1a (454,200 molecular weight) and ORF1a/1b (754,200 molecular weight) have been compared to the predicted RNA polymerase gene products of infectious bronchitis virus (IBV) and murine hepatitis virus (MHV) and conserved structural features and putative functional domains have been identified. This analysis completes the nucleotide sequence of the HCV 229E genome.

Genetic dissection of signal transduction mediated by the sevenless receptor tyrosine kinase in Drosophila

The specification of the R7 photoreceptor cell fate in the developing eye of Drosophila depends on the local activation of the sevenless (Sev) receptor tyrosine kinase by Boss, a protein expressed on the membrane of the neighbouring R8 cell. Constitutive activation of the Sev receptor results in a dosage-dependent increase in the number of R7 cells per ommatidium. Genetic screens have been used to identify mutations that alter the efficiency of signal transduction. Subsequent molecular characterization of the corresponding genes has led to the identification of a number of proteins involved in transducing the signal from the receptor to the nucleus. In contrast to the receptor and its ligand, these components are shared between different signal transduction pathways not only in Drosophila but are also homologous to components involved in signal transduction in other organisms.

A Drosophila SH2-SH3 adaptor protein implicated in coupling the sevenless tyrosine kinase to an activator of Ras guanine nucleotide exchange, Sos

A Drosophila gene (drk) encodes a widely expressed protein with a single SH2 domain and two flanking SH3 domains, which is homologous to the Sem-5 protein of C. elegans and mammalian GRB2. Genetic analysis suggests that drk function is essential for signaling by the sevenless receptor tyrosine kinase. Drk biological activity correlates with binding of its SH2 domain to activated receptor tyrosine kinases and concomitant localization of drk to the plasma membrane. In vitro, drk also binds directly to the C-terminal tail of Sos, a Ras guanine nucleotide-releasing protein (GNRP), which, like Ras1 and drk, is required for sevenless signaling. These results suggest that drk binds autophosphorylated receptor tyrosine kinases with its SH2 domain and the Sos GNRP through its SH3 domains, thereby coupling receptor tyrosine kinases to Ras activation. The conservation of these signaling proteins during evolution indicates that this is a general mechanism for linking tyrosine kinases to Ras.

Molecular analysis of the human coronavirus (strain 229E) genome

The nucleotide sequence of the human coronavirus strain 229E (HCV 229E) has been determined. This article describes the organization of the virus genome, the predicted viral gene products and the mechanisms which regulate viral gene expression. This information provides a basis to investigate the biology and pathogenesis of HCV.

Primary structure and expression of bovine poly(A) polymerase

Poly(A) polymerase has a critical role in the synthesis of messenger RNA in eukaryotic cells. The isolation and characterization of complementary DNAs encoding bovine poly(A) polymerase is described here. The predicted sequences of the mRNA and protein reveal features that provide insights into how the enzyme functions and how it might be regulated. Poly(A) polymerase expressed from a cloned cDNA is fully functional in in vitro assays, and mutational analyses have identified a putative regulatory domain that enhances, but is not essential for, activity.

The rat interleukin-5 gene: characterization and expression by retroviral gene transfer and polymerase chain reaction

The rat interleukin-5 (IL-5) gene was isolated from a genomic lambda phage library and a fragment containing all four exons was inserted into the retroviral vector pXT1, resulting in pXTRIL5. Upon retroviral gene transfer into two IL-5-dependent mouse cell lines, B13 and T88M, autonomously growing cells were established and B-cell growth factor activity was detected in the supernatants of the infected cells. "cDNA" versions of the rat IL-5 gene were rescued by the polymerase chain reaction (PCR) with primers specific for the flanking regions of the cloning site in pXT1. Restriction or DNA sequence analysis of five different clones revealed precise splicing in two cases, while three of the clones had retained the first intron. In addition, in two of these about 400 bp of rat IL-5 5' flanking regions were deleted. The sequence comparison of rat, mouse, and human IL-5 genes revealed a high degree of conservation (e.g., mouse and rat were 92% homologous at the amino acid level). The combination of retroviral gene transfer and PCR may offer an alternative, efficient method for the cloning of cDNAs.

Characterization of a nucleic acid probe for the diagnosis of human coronavirus 229E infections

A cDNA copy of the HCV229E nucleocapsid protein gene was isolated and characterized. Sequence analysis predicts a nucleocapsid polypeptide of 389 amino acids with a molecular weight (mol. wt.) of 43,450. Single strand RNA probes derived from the cDNA copy hybridize specifically to HCV229E RNA and approximately 50 pg of intracellular viral RNA can be readily detected. The application of nucleic acid hybridization as a routine procedure for the diagnosis of HCV229E infection is discussed.

Nucleotide sequence of the gene encoding the spike glycoprotein of human coronavirus HCV 229E

The gene encoding the spike glycoprotein of the human coronavirus HCV 229E has been cloned and sequenced. This analysis predicts an S polypeptide of 1173 amino acids with an Mr of 128,600. The polypeptide has 30 potential N-glycosylation sites. A number of structural features typical of coronavirus S proteins can be recognized, including a signal sequence, a membrane anchor, heptad repeat structures and a carboxy-terminal cysteine cluster. A detailed, computer-aided comparison with the S proteins of infectious bronchitis virus, feline infectious peritonitis virus, transmissible gastroenteritis virus and murine hepatitis virus, strain JHM is presented. We have also done a Northern blot analysis of viral RNAs in HCV 229E-infected cells using synthetic oligonucleotides. On the basis of this analysis, and by analogy to the replication strategy of other coronaviruses, we are able to propose a model for the organization and expression of the HCV 229E genome.

Nucleotide sequence of the gene encoding the membrane protein of human coronavirus 229 E

The sequence of the gene encoding the membrane protein of human coronavirus 229 E (HCV 229 E) has been determined. The primary translation product, deduced from the DNA sequence, is a polypeptide of 225 amino acids with a predicted molecular weight of 26,000. The polypeptide has 3 potential N-glycosylation sites. Many structural similarities with the membrane proteins of other coronaviruses can be recognized.

A selection cartridge for rapid detection and analysis of spontaneous mutations including insertions of transposable elements in Enterobacteriaceae

We present a method that allows positive selection and rapid analysis of mutations in Enterobacteriaceae. Mutations are detected in a 2630 bp selection cartridge inserted in two different bacterial multicopy plasmid vectors. Spontaneous mutations in Escherichia coli, Enterobacter cloacae and Citrobacter freundii include insertions, deletions and point mutations. The small size of the target sequence facilitates rapid analysis of DNA rearrangements by cleavage with restriction enzymes and of any type of mutation by DNA sequence analysis. While in E. coli insertions of the mobile elements IS1, IS2 and IS5 were readily found, insertions of putative new transposable elements were detected in Enterobacter cloacae. The selection cartridge can thus serve as a tool for studying the spectrum of insertion mutations in Enterobacteriaceae and probably other Gram-negative bacteria, and the dependency of this spectrum on physiological and environmental factors and the host's genetic background can be investigated.

Identification of the coronavirus MHV-JHM mRNA 4 product

A bacterial expression vector was constructed to encode a fusion protein which had, at its carboxy terminus, a polypeptide encoded within the 5' proximal open reading frame of the coronavirus MHV-JHM mRNA 4. This polypeptide was isolated and used to produce an antiserum. The antiserum reacted specifically with a 15,000 Mr polypeptide synthesized in MHV-JHM-infected cells, or in vitro translations of infected cell poly(A) RNA enriched for mRNA 4. These results demonstrate the translational activity of mRNA 4 during infection, identify conclusively the translation product and provide a means to investigate the synthesis and function of this protein.