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Sequence of the phosphoprotein gene of pneumonia virus of mice: expression of multiple proteins from two overlapping reading frames.

The gene encoding the phosphoprotein of the pneumovirus pneumonia virus of mice (PVM) has been cloned and sequenced. The gene is 903 nucleotides in length and contains a long open reading frame (ORF) capable of encoding a polypeptide of 295 amino acid residues. A smaller, second, overlapping ORF encoding a polypeptide 137 amino acids in length was also present. The large ORF directed the synthesis of a 39-kDa polypeptide and four additional polypeptides with masses of 37 kDa, 26 kDa, 23 kDa, and 16 kDa in vitro. The smaller polypeptides were generated by internal initiation on in-frame AUG initiation codons to generate carboxy co-terminal products. Western immunoblot analysis indicated that at least two of these proteins and several other related polypeptides are present in infected cells, and the possible origins of these are discussed. Western blot analysis using antiserum raised against a synthetic peptide and specific for the predicted second ORF product identified a polypeptide of 23 kDa in PVM-infected cells. The pattern of PVM P gene expression is unlike that of the closely related respiratory syncytial virus and is reminiscent of that of paramyxoviruses such as Sendai virus. This is the first example of a pneumovirus encoding multiple polypeptide products from a single mRNA in vivo.

Amino Acid Sequence↗

Construction and characterization of a humanized single chain Fv antibody fragment against the main immunogenic region of the acetylcholine receptor.

The single chain Fv fragment of mAb198 (scFv198) directed against the main immunogenic region (MIR) of the nicotinic acetylcholine receptor (AChR), can efficiently protect the AChR in muscle cell cultures against the destructive activity of human myasthenic autoantibodies. Humanization of the scFv198 antibody fragment should prove useful for therapeutic application by reducing its immunogenicity. Framework sequences from human immunoglobulins homologous to the rat scFv198 sequences were selected and a totally synthetic humanized scFv198 antibody fragment was constructed in vitro. Humanized VH and VL domains were synthesized using two overlapping sets of 225 bases long oligonucleotides overlap extension and polymerase chain reaction (PCR), then assembled into a full-length gene by overlap extension of single-stranded DNA (ssDNA) fragments and PCR. The initial humanized antibody fragment had a very low affinity for the AChR. Molecular modeling was then performed and four residues from the framework regions (FR) of the humanized VH domain were selected to be replaced by the corresponding amino acid from the rat sequence. Three mutants were constructed by overlap extension, using PCR. The humanized variant containing replacements at VH residues 27, 29, 30 and 71 showed very good recovery of AChR binding activity; its binding affinities for Torpedo or human AChR (K(D): 8.5 or 323 nM, respectively) being only four times lower than those of the parental scFv198 (K(D): 2 or 80 nM, respectively). This variant was able to protect the human AChR against the binding of anti-MIR mAb and anti-alpha autoantibodies from a myasthenic patient. It was also able to protect AChR against antigenic modulation induced by the anti-MIR mAb198.

Animals↗

Overlapping expression of amphioxus homologs of the thyroid transcription factor-1 gene and thyroid peroxidase gene in the endostyle: insight into evolution of the thyroid gland.

The endostyle is a pharyngeal organ of uro- chordates, cephalochordates, and primitive vertebrates. This organ has iodine-concentrating and iodine-metabolism activities, and therefore the endostyle is considered to be homologous to the follicle of the thyroid gland. In higher vertebrates the genes for both thyroid transcription factor-1 (TTF-1) and thyroid peroxidase (TPO) are expressed in the thyroid gland follicle. TTF-1 regulates the expression of TPO, which encodes an iodinating enzyme associated with thyroid hormone synthesis. A recent study showed that the ascidian TTF-1 and TPO genes are specifically expressed in the endostyle, but that the expression domains of these genes are not overlapping, suggesting that ascidian TPO is not regulated by TTF-1. To investigate the molecular mechanisms involved in the formation and function of the endostyle, with special reference to the evolution of the follicle of the thyroid gland, I isolated and characterized cDNA clones for the amphioxus homologs of the TTF-1 gene (BbTTF-1) and TPO gene (BbTPO) from Branchiostoma belcheri. Reverse transcriptase-polymerase chain reaction/Southern blotting revealed that both amphioxus TTF-1 and TPO genes are expressed mainly in the adult endostyle. Spatial and temporal expression patterns assessed by in situ hybridization revealed that BbTTF-1 is expressed in the endodermal cells during early embryogenesis and is maintained in all zones of the adult endostyle. On the other hand, expression of BbTPO is chiefly in zones 5 and 6 of the adult endostyle where it overlaps with that of BbTTF-1, and to a lesser extent in zones 1 and 3. This restriction of the expression of BbTTF-1 and BbTPO to the endostyle strongly suggests that the endostyle is homologous to the follicle of the thyroid gland. Moreover, the spatial and temporal expression patterns of these genes suggest that TTF-1 regulates TPO expression. The coexpression of these genes in amphioxus suggests that regulation of TPO by TTF-1 was present in the common ancestor of cephalochordates (acraniates) and craniates.

Amino Acid Sequence↗

The multifunctional regulatory proteins ABF1 and CPF1 are involved in the formation of a nuclease-hypersensitive region in the promoter of the QCR8 gene.

The abundant DNA-binding proteins ABF1 and CPF1 are members of a family of global regulators with diverse chromosomal functions in the yeast Saccharomyces cerevisiae. Recent evidence suggests that these protein factors may be involved in establishing and maintaining well-defined chromatin in promoter regions and other genetic elements. We have investigated the involvement of ABF1 and CPF1 in chromatin organization at the QCR8 gene, encoding subunit VIII of the mitochondrial ubiquinol-cytochrome c oxidoreductase. The promoter region of the QCR8 gene contains overlapping binding sites for ABF1 and CPF1. Nucleosome positioning studies indicate that the QCR8 gene is associated with a phased array of nucleosomes under both catabolite-repressed and derepressed growth conditions. Analysis of binding site mutants reveals that both ABF1 and CPF1 are involved in maintaining a nuclease-hypersensitive region in the QCR8 promoter. The chromatin structure at QCR8 during steady-state growth is, however, mainly dependent on binding of ABF1 to the promoter region. Implications of these findings for the role played by ABF1 and CPF1 in the regulation of mitochondrial biogenesis and other processes important for cell growth and division will be discussed.

Basic Helix-Loop-Helix Leucine Zipper Transcriptio↗

Gene conversion and the evolution of three leucine-rich repeat gene families in Arabidopsis thaliana.

The high number of duplicated genes in plant genomes provides a potential template for gene conversion and unequal crossing-over. Within a gene family these two processes can render all members homogeneous or generate diversity by reassorting variants among paralogs. The latter is especially feasible in families where gene diversity confers a selective advantage and thus conversion events are likely to be retained. Consequently, the most complete record of gene conversion is expected to be most evident in gene families commonly subjected to positive selection. Here, we describe the extent and characteristics of gene conversion and unequal crossing-over in the coding and noncoding regions of nucleotide-binding site leucine-rich repeat (NBS-LRR), receptor-like kinases (RLK), and receptor-like proteins (RLP) in the plant Arabidopsis thaliana. Members of these three gene families are associated with disease resistance and their pathogen-recognition domain is a documented target of positive selection. Our bioinformatic approach to study the major family features that may influence gene conversion revealed that in these families there is a significant association between the occurrence of gene conversion and high levels of sequence similarity, close physical clustering, gene orientation, and recombination rate. We discuss these results in the context of the overlap between gene conversion and positive selection during the evolutionary expansion of the NBS-LRR, RLK, and RLP gene families.

Arabidopsis↗

Individual Mycobacterium tuberculosis resuscitation-promoting factor homologues are dispensable for growth in vitro and in vivo.

Mycobacterium tuberculosis possesses five genes with significant homology to the resuscitation-promoting factor (Rpf) of Micrococcus luteus. The M. luteus Rpf is a secreted approximately 16-kDa protein which restores active growth to cultures of M. luteus rendered dormant by prolonged incubation in stationary phase. More recently, the Rpf-like proteins of M. tuberculosis have been shown to stimulate the growth of extended-stationary-phase cultures of Mycobacterium bovis BCG. These data suggest that the Rpf proteins can influence the growth of mycobacteria; however, the studies do not demonstrate specific functions for the various members of this protein family, nor do they assess the function of M. tuberculosis Rpf homologues in vivo. To address these questions, we have disrupted each of the five rpf-like genes in M. tuberculosis Erdman, and analyzed the mutants for their growth in vitro and in vivo. In contrast to M. luteus, for which rpf is an essential gene, we find that all of the M. tuberculosis rpf deletion mutant strains are viable; in addition, all show growth kinetics similar to Erdman wild type both in vitro and in mouse organs following aerosol infection. Analysis of rpf expression in M. tuberculosis cultures from early log phase through late stationary phase indicates that expression of the rpf-like genes is growth phase-dependent, and that the expression patterns of the five M. tuberculosis rpf genes, while overlapping to various degrees, are not uniform. We also provide evidence that mycobacterial rpf genes are expressed in vivo in the lungs of mice acutely infected with virulent M. tuberculosis.

Animals↗

Molecular structure of a functional rat gene for manganese-containing superoxide dismutase.

The manganese-containing superoxide dismutase (MnSOD) constitutes one of the major cellular defense mechanisms against the toxic effects of superoxide radical. The development of tolerance in adult rats to lethal exposure of O2 (100%) after pre-exposing them to a sublethal concentration of O2 (85%) was found to be closely associated with the increased activity of this enzyme in the lungs. Further experiments have shown that the transcriptional rate of the gene coding for MnSOD in rat lungs is increased at day 3 of 85% O2 exposure. To elucidate the nature of this transcriptional activation during hyperoxic insults, we chose to first understand the structure of the rat MnSOD gene. Three overlapping rat genomic fragments were isolated, and the DNA sequence containing the whole MnSOD gene was completely determined. The rat MnSOD gene contains at least five exons and is located in one piece of 16.4-kb EcoRI genomic DNA fragment. However, Southern blot analysis of total rat genomic DNA probed with MnSOD cDNA revealed an additional hybridizing 8.6-kb EcoRI genomic fragment besides the 16.4-kb one. To clarify the origin of this unexpected hybridizing genomic fragment, three unique genomic sequences derived from the promoter, intron 2, and the 3' untranslated region of the genomic clones were used to rehybridize the same Southern blot filter and were found to only hybridize to the 16.4-kb but not 8.5-kb EcoRI genomic fragment. These data suggest: (1) two MnSOD genes are present per haploid rat genome, and (2) all three cloned genomic fragments are derived from the MnSOD gene, which is located in the 16.4-kb EcoRI genomic fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

Control of thyroglobulin gene transcription by TSH and cAMP.

The availability of the sequence of Tg promoter from three different species enabled a fruitful comparison to be made from which a general picture of the organization of the Tg gene promoter region emerged. Chromatin structure studies identified tissue-specific modifications at the level of DNA protein interactions. A DNA element has been shown to be involved in transcription control by cAMP. This sequence includes a highly conserved region of the Tg gene promoter, overlaps a domain of the promoter which becomes hypersensitive to DNase I when the gene is expressed and displays specific protein-DNA interaction. These observations are consistent with the possibility that this sequence is a target element for trans-acting factor(s) which control(s) the transcriptional activity of the gene.

Animals↗

A direct and efficient PAGE-mediated overlap extension PCR method for gene multiple-site mutagenesis.

A simple, two-step efficient method to perform multiple-site mutagenesis of a gene from bacterial genome was developed. The method was named polyacrylamide gel electrophoresis (PAGE)-mediated overlap extension polymerase chain reaction (PCR) (POEP). The first step involves synthesis of individual fragments containing mutant sites with 15- to 25-bp overlap between two adjacent fragments. Mutations were introduced into the overlapping oligonucleotide primers which ensured the particular primer-template annealing. PAGE was used to remove contaminating parental templates, mispriming fragments, and leftover primers. The second step involves synthesis of the mutant full-length fragment. All purified PCR products from the first step were combined and used as the template for a second PCR using high-fidelity DNA polymerase, with the two outermost flanking oligonucleotides as primers. Using the POEP method, we have successfully introduced eight EcoRI sites into the Escherichia coli beta-galactosidase (Lac Z) gene. The overall rate of obtaining the multiple mutant sites was 100%. The POEP method is simple, involving only two steps, and reliable for multiple-site mutagenesis and is promising to be widely used in gene modification.

DNA, Bacterial↗

Abundant adrenal-specific transcription of the human P450c21A "pseudogene".

Human adrenal steroid 21-hydroxylase (P450c21) is encoded by the CYP21A1 (21B) gene located in the class III region of the HLA locus. A tandemly duplicated gene designated CYP21A1P (21A), which lies 30 kilobases upstream, contains several point mutations and an 8-base pair deletion so that it cannot encode P450c21 protein; as a result, it is generally considered to be a pseudogene. We previously showed that two additional genes, XA and XB, lie on the opposite strand of DNA overlapping the 3'-ends of the 21A and 21B genes. We have now identified a third pair of duplicated overlapping genes in this locus, termed YA and YB, whose transcriptional orientation is the same as 21A and 21B and opposite to XA and XB. YA transcripts use the 21A promoter, have 5'-ends that are similar to 21B mRNA, and have approximately 10-20% of the abundance of 21B transcripts, but have unique 3'-ends. The YA gene encodes a 7.5-kilobase RNA that overlaps XA completely and a 3.0-kilobase RNA that excludes most of XA. The YB gene appears to be similar in size and organization to YA. The YA and YB genes extend beyond the limit of the duplication in this locus; hence, their cDNAs are distinguishable by differences in their 3'-sequences. YA and YB transcripts are expressed only in the fetal and adult adrenal glands, but their cDNAs do not contain a long open reading frame. Although the function of these genes is not yet clear, the complex genetic organization of three overlapping genes (21/X/Y) appears to be unique among higher eukaryotes. As YA transcription is initiated by the 21A 5'-flanking DNA and includes 21A sequences, the designation of 21A as a "pseudogene" merits reconsideration.

Adrenal Glands↗

Alternative non-coding splice variants of Nespas, an imprinted gene antisense to Nesp in the Gnas imprinting cluster.

The Gnas locus on mouse Chr 2 represents a unique cluster of overlapping imprinted genes. Three of these in the order Nesp--Gnasxl--Gnas are transcribed in the sense direction with Nesp having maternal-specific expression, Gnasxl having paternal expression, and Gnas as being biallelically expressed in most tissues. A fourth imprinted gene, Nespas, is paternally expressed, lies antisense to Nesp, and expresses an unspliced transcript. Large unspliced antisense transcripts are emerging as a feature of imprinted gene clusters, and such non-coding RNAs may have a cis-regulatory function. Here we show that, in addition to an unspliced form of Nepas, we can detect five alternatively spliced forms of Nespas up to 1.4 kb in length that are non-coding. The splice variants are paternally expressed; they start approximately 2 kb upstream of Gnasxl in a region of maternal methylation and end 2.5 kb beyond the ATG of Nesp. These variants do not correspond to exons of the human antisense transcript although they start in the same region; the Nespas transcript, like its human counterpart, is spliced in various alternative patterns. The identification of a set of small spliced imprinted transcripts in the human and now in the mouse suggests that these antisense transcripts are functionally important.

Alternative Splicing↗

Diverse signaling pathways activated by growth factor receptors induce broadly overlapping, rather than independent, sets of genes.

We sought to explore the relationship between receptor tyrosine kinase (RTK) activated signaling pathways and the transcriptional induction of immediate early genes (IEGs). Using global expression monitoring, we identified 66 fibroblast IEGs induced by platelet-derived growth factor beta receptor (PDGFRbeta) signaling. Mutant receptors lacking binding sites for activation of the PLCgamma, PI3K, SHP2, and RasGAP pathways still retain partial ability to induce 64 of these IEGs. Removal of the Grb2-binding site further broadly reduces induction. These results suggest that the diverse pathways exert broadly overlapping effects on IEG induction. Interestingly, a mutant receptor that restores the RasGAP-binding site promotes induction of an independent group of genes, normally induced by interferons. Finally, we compare the PDGFRbeta and fibroblast growth factor receptor 1; each induces essentially identical IEGs in fibroblasts.

3T3 Cells↗

Large-scale identification and characterization of human genes that activate NF-kappaB and MAPK signaling pathways.

We have carried out a large-scale identification and characterization of human genes that activate the NF-kappaB and MARK signaling pathways. We constructed full-length cDNA libraries using the oligo-capping method and prepared an arrayed cDNA pool consisting of 150 000 cDNAs randomly isolated from the libraries. For analysis of the NF-kappaB signaling pathway, we introduced each of the cDNAs into human embryonic kidney 293 cells and examined whether it activated the transcription of a luciferase reporter gene driven by a promoter containing the consensus NF-kappaB binding sites. In total, we identified 299 cDNAs that activate the NF-kappaB pathway, and we classified them into 83 genes, including 30 characterized activator genes of the NF-kappaB pathway, 28 genes whose involvement in the NF-kappaB pathways have not been characterized and 25 novel genes. We then carried out a similar analysis for the identification of genes that activate the MARK pathway, utilizing the same cDNA resource. We assayed 145 000 cDNAs and identified 57 genes that activate the MARK pathway. Interestingly, 27 genes were overlapping between the NF-kappaB and the MAPK pathways, which may indicate that these genes play cross-talking roles between these two pathways.

Amino Acid Sequence↗

Genome-wide analysis of ARS (autonomously replicating sequence) binding factor 1 (Abf1p)-mediated transcriptional regulation in Saccharomyces cerevisiae.

Autonomously replicating sequence-binding factor-1 (Abf1p) is an essential sequence-specific transcription factor in Saccharomyces cerevisiae that participates in multiple nuclear events including DNA replication, transcription activation, and gene silencing. Numerous gene-specific analyses have implicated Abf1p in the transcriptional control of genes involved in a diverse range of cellular functions, leading to the notion that Abf1p acts as a global transcriptional regulator. Here we report findings from a genome-wide comparison of the gene expression profiles in the wild-type and abf1-1 temperature-sensitive mutant. The study identifies a total of 86 Abf1p-regulated genes (1.4% of the genome) of which 50 are activated and 36 are repressed by Abf1p. Interestingly, Abf1p binds to its own promoter in vivo and strongly represses its own transcription, suggesting a potential negative regulatory loop in Abf1p-mediated gene regulation. A comparison of our microarray data with the available databases reveals a significant overlap of genes regulated by Abf1p and those by several general transcription factors such as Mot1p and TAFs (TATA-binding protein-associated factors). Different mutant alleles of abf1 affect Abf1p-mediated transcription in a gene-dependent manner. Furthermore, Abf1p in vivo is associated with the promoter region of most Abf1p-activated but not with that of most Abf1p-repressed genes. Taken together, these results strongly suggest distinct underlying mechanisms by which Abf1p regulates gene expression.

5' Untranslated Regions↗

The Arabidopsis R2R3 MYB proteins FOUR LIPS and MYB88 restrict divisions late in the stomatal cell lineage.

The two guard cells of a stoma are produced by a single symmetric division just before terminal differentiation. Recessive mutations in the FOUR LIPS (FLP) gene abnormally induce at least four guard cells in contact with one another. These pattern defects result from a persistence of precursor cell identity that leads to extra symmetric divisions at the end of the cell lineage. FLP is likely to be required for the correct timing of the transition from cell cycling to terminal differentiation. FLP encodes a two-repeat (R2R3) MYB protein whose expression accumulates just before the symmetric division. A paralogous gene, MYB88, overlaps with FLP function in generating normal stomatal patterning. Plants homozygous for mutations in both genes exhibit more severe defects than flp alone, and transformation of flp plants with a genomic MYB88 construct restores a wild-type phenotype. Both genes compose a distinct and relatively basal clade of atypical R2R3 MYB proteins that possess an unusual pattern of amino acid substitutions in their putative DNA binding domains. Our results suggest that two related transcription factors jointly restrict divisions late in the Arabidopsis thaliana stomatal cell lineage.

Amino Acid Substitution↗

Gene expression in splenic CD4 and CD8 cells from BALB/c mice immunized with Porphyromonas gingivalis.

BACKGROUND: T cells are fundamental in the pathogenesis of periodontal disease. Suppression of cell-mediated responses is associated with disease progression together with the concomitant increase in plaque pathogens including Porphyromonas gingivalis. The aim of the present study was to examine gene expression in T cells in response to P. gingivalis in mice. METHODS: BALB/c mice were given weekly intraperitoneal injections of P. gingivalis outer-membrane antigens with Freund's incomplete adjuvant for 3 weeks, whereas control mice received phosphate buffered saline (PBS) and adjuvant only. Splenic CD4 and CD8 subpopulations were isolated by magnetic cell separation and their responses investigated using microarray analysis. RESULTS: Most genes coded for enzymes concerned with metabolic pathways. Only five and 28 genes, respectively, were upregulated in CD4 and CD8 cells extracted from P. gingivalis-immunized mice, including immunoglobulin (Ig) heavy-chain genes for IgG1 and IgG2a in CD4 cells. In contrast, 1,141 and 1,175 genes, respectively, were downregulated. A total of 60 and 65 genes, respectively, coded for immune response proteins or those relevant to periodontal disease pathogenesis. The overlap of genes in the two subsets was 21%. One of the major effects, apart from T-cell function suppression, was the shift away from Th1 responses, although there was also a downregulation of two genes and upregulation of one Th2-response gene. Genes downregulated included those encoding cytokines, proteins involved in Ig binding, antigen presentation, innate immunity, extracellular matrix, and cell adhesion molecules that could result in dysregulation in the progressive periodontal lesion. CONCLUSIONS: Early findings in humans demonstrated that periodontopathic bacteria induce immunosuppressive effects on T cells. The present study has shown that P. gingivalis had a predominant downregulatory effect on gene expression in CD4 and CD8 T cells in mice.

Animals↗

Mechanism of translation of the hepadnaviral polymerase (P) gene.

Unlike many other reverse transcriptase genes, the polymerase (P) gene of the hepatitis B viruses is expressed by translational initiation from its own AUG codon rather than by ribosomal frameshifting during translation of the overlapping core gene (C). To explore the mechanism of its translation, we have fused the P gene of duck hepatitis B virus to the bacterial lacZ gene at a point 3' to the C-P overlap; this allows detection of the products of P translation with antisera to the lacZ-encoded protein. The C and P/Z coding regions were cloned downstream of a heterologous promoter and expressed in COS-7 cells. A single, bicistronic mRNA containing both C and P sequences is detected in these cells, and translational initiation occurs efficiently at the internally situated P AUG. Mutations affecting C translation have only minimal effects on P expression, in contrast to what would be expected from a modified scanning model for translation. We conclude that P translation depends on a mechanism other than scanning to allow internal entry of ribosomes to the region of the P initiator.

Animals↗

Orphan receptor HNF-4 and bZip protein C/EBP alpha bind to overlapping regions of the apolipoprotein B gene promoter and synergistically activate transcription.

As the sole protein component of low density lipoproteins, apolipoprotein B (apoB) plays an important role in cholesterol metabolism. Previously, we found that the proximal promoter region of apoB (-81 to -52 relative to the start site) played a critical role in hepatocyte-specific gene expression and that that region contained overlapping binding sites for nuclear factors AF-1 (-81 to -62) and C/EBP (-69 to -52) (Metzger, S., Leff, T., and Breslow, J. L. (1990) J. Biol. Chem. 265, 9978-9983). In this study, we show that HNF-4, a member of the steroid hormone receptor superfamily, binds the AF-1 site on the apoB promoter and through it activates transcription in transient transfection assays in both liver and non-liver cell lines, HepG2 and HeLa, respectively. Mutational analysis of the AF-1/HNF-4 binding site indicated a correlation of HNF-4 binding and transcriptional activity. In addition, transient co-transfection experiments with HNF-4 and C/EBP alpha expression vectors showed that the two factors can synergistically activate transcription to levels more than 3-fold above the sum of either factor alone. Finally, using gel retardation analysis we show that purified HNF-4 and C/EBP proteins can concurrently occupy their overlapping binding sites on the apoB promoter in vitro. However, since the same system showed a lack of cooperative binding, we argue that an alternative mechanism is responsible for the synergistic effect of HNF-4 and C/EBP alpha on apoB gene transcription.

Apolipoproteins B↗