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A Mergia

Publications and source records attributed to A Mergia.

31 records · Page 2Linked to original sources
PubMed1993

Functional domains of the simian foamy virus type 1 transcriptional transactivator (Taf).

The genome of simian foamy virus type 1 encodes a transcriptional transactivator (Taf) that dramatically elevates gene expression directed by the viral long terminal repeat. In this report, we describe the functional domains of simian foamy virus type 1 Taf. Several taf mutants and fusion proteins of Taf and the DNA-binding domain of the Saccharomyces cerevisiae transcriptional transactivator GAL4 were used in this study. Taf contains two potent activation domains. One of the activation domains is located at the amino terminus (positions 1 to 48, with position 1 representing the initiator amino acid methionine) and contains several acidic amino acids. The second activation domain was mapped to a region at the carboxy terminus (positions 277 to 300). These two domains activate gene expression directed by the viral long terminal repeat independently of each other. No significant amino acid sequence homology between the activation domains is noted. Thus, Taf belongs in part to the family of acidic transcriptional transactivators. The activation domain at the carboxy terminus is conserved among foamy virus transactivators but is not related to other known transcriptional activators. Therefore, the mechanism of gene activation by the carboxy terminus of Taf may be novel. In addition, a potential binding domain rich in basic amino acids (positions 179 to 222) and a highly conserved sequence among foamy virus transactivators (positions 93 to 109) were found to be critical for Taf activity.

Amino Acid Sequence↗
PubMed1992

cis-acting regulatory regions in the long terminal repeat of simian foamy virus type 1.

Simian foamy virus type 1 (SFV-1), a member of the Spumavirinae subfamily of retroviruses, encodes a transcriptional transactivator (taf) that strongly augments gene expression directed by the viral long terminal repeat (LTR) (A. Mergia, K. E. S. Shaw, E. Pratt-Lowe, P. A. Barry, and P. A. Luciw, J. Virol. 65:2903-2909, 1991). This report describes cis-acting regulatory elements in the LTR that control viral gene expression. A series of LTR mutants and hybrid promoter constructs have been analyzed in transient expression assays for responsiveness to Taf. The targets for transactivation have been mapped to two regions of the U3 domain of the LTR, between positions -1196 and -880 and between positions -403 and -125 (+1 represents the transcription initiation site). No significant nucleotide sequence homology between these two regions is noted; thus, the SFV-1 taf gene acts through at least two distinct sequence elements in the LTR. The target contained between positions -403 and -125 acts independently of orientation, in different cell types and species, and in the context of a heterologous promoter. Thus, the target element between positions -403 and -125 has properties of a transcriptional enhancer. The observation that two distinct elements in the SFV-1 LTR are targets for transcriptional transactivation is novel with respect to observations for other retroviral systems. The R-U5 region of the SFV-1 LTR down-regulates transactivation by severalfold. Computer analysis of the R-U5 region revealed a secondary structure with a free-energy level of -74 kcal (ca. -310,000 J); this structural feature may account for the inhibitory effect on gene expression directed by the LTR. Taf of SFV-1 had no effect on gene expression directed by the LTR of the related human foamy virus, whereas Taf transactivates gene expression directed by the LTRs of the human and simian immunodeficiency viruses. Comparative functional analysis of Taf on homologous and heterologous LTRs may facilitate elucidation of the mechanism of transactivation of foamy viruses.

Animals↗
PubMed1991

Identification of the simian foamy virus transcriptional transactivator gene (taf).

Simian foamy virus type 1 (SFV-1), a member of spumavirus subfamily of retroviruses, encodes a transcriptional transactivator that functions to strongly augment gene expression directed by the viral long terminal repeat (LTR). The objective of this study was to identify the viral gene responsible for transactivation. Nucleotide sequences between the env gene and the LTR of SFV-1 were determined. The predicted amino acid sequence revealed two large open reading frames (ORFs), designated ORF-1 (311 amino acids) and ORF-2 (422 amino acids). In the corresponding region of the human foamy virus, three ORFs (bel-1, bel-2, and bel-3) have been identified (R. M. Flugel, A. Rethwilm, B. Maurer, and G. Darai, EMBO J. 6:2077-2084, 1987). Pairwise comparisons of the ORF-1 and ORF-2 with bel-1 and bel-2 show small clusters of homology; less than 39% overall homology of conserved amino acids is observed. A counterpart for human foamy virus bel-3 is not present in the SFV-1 sequence. Three species of viral RNA have been identified in cells infected with SFV-1; an 11.5-kb RNA representing full-length transcripts, a 6.5-kb RNA representing the env message, and a 2.8-kb RNA from the ORF region. Analysis of a cDNA clone encoding the ORF region of SFV-1 reveals that the 2.8-kb message is generated by complex splicing events involving the 3' end of the env gene. In transient expression assays in cell lines representing several species. ORF-1 was shown to be necessary and sufficient for transactivating viral gene expression directed by the SFV-1 LTR. The target for transactivation is located in the U3 domain of the LTR, upstream from position - 125 (+ 1 represents the transcription initiation site). We propose that OFF-1 of SFV-1 be designated the transcriptional transactivator of foamy virus (taf).

Amino Acid Sequence↗
PubMed1990

Relationship of the env genes and the endonuclease domain of the pol genes of simian foamy virus type 1 and human foamy virus.

We have molecularly cloned and sequenced a portion of the simian foamy virus type 1 (SFV-1); open reading frames representing the endonuclease domain of the polymerase (pol) and the envelope (env) genes were identified by comparison with the human foamy virus (HFV). Unlike the HFV genomic organization, the SFV-1 pol gene overlaps the env gene; thus, the open reading frames reported for HFV between pol and env is not present in SFV-1. Comparisons of predicted amino acid sequences of HFV and SFV-1 reveal that the endonuclease domains of the pol genes are about 84% related. The region predicted to encode the SFV-1 extracellular env domain is 569 codons; SFV-1 and HFV have 64% amino acid similarity in this env domain. The predicted hydrophobic transmembrane env proteins of both HFV and SFV-1 show about 73% similarity. A total of 16 potential glycosylation sites are found in SFV-1 env, and 15 are found in HFV; 11 are shared. SFV-1 has 25 cysteine residues, and HFV has 23 residues; all 23 cysteine residues of HFV are conserved in SFV-1. This sequence analysis reveals that the human and simian foamy viruses are highly related.

Amino Acid Sequence↗
PubMed1990

Simian foamy virus type 1 is a retrovirus which encodes a transcriptional transactivator.

Simian foamy viruses, members of the spumavirus subfamily of retroviruses, are found in a variety of nonhuman primates and, as yet, remain to be characterized with respect to genetic structure and regulation of viral gene expression. The genome of simian foamy virus type 1 (SFV-1), an isolate from rhesus macaques, has been molecularly cloned, and the role of the viral long terminal repeat (LTR) in transcriptional control has been investigated. The SFV-1 LTR is 1,621 base pairs long, and sequence comparisons with human foamy virus revealed a pattern of clustered homology. A cap site in the LTR was identified by analysis of SFV-1 transcripts in infected cells. Transient expression assays in cell lines representing several species and different cell types showed that the SFV-1 LTR has low basal activity in uninfected cells, whereas LTR-directed expression is greatly increased in cells infected with SFV-1. This transactivation is mediated by a mechanism involving increases in steady-state levels of viral transcripts. Thus, the SFV-1 genome encodes a transactivator that functions on the LTR at the transcriptional level.

Animals↗
PubMed1989

Structural analysis of the gene for human acidic fibroblast growth factor.

Genomic clones derived from the gene for human acidic fibroblast growth factor (aFGF) have been isolated. Nucleotide sequence analysis of these clones revealed that the coding region of the human aFGF gene is interrupted by two introns, located at precisely homologous locations to introns in four other members of the FGF gene family, strongly indicating a common evolutionary origin for these genes. Northern blot analyses of the multiple aFGF transcripts found in serum-stimulated human foreskin fibroblasts indicated that the aFGF gene also contains a third intron, lying in the 5' untranslated region.

Amino Acid Sequence↗
PubMed1987

Basic fibroblast growth factor in human rhabdomyosarcoma cells: implications for the proliferation and neovascularization of myoblast-derived tumors.

Cultured human embryonal rhabdomyosarcoma cells express the basic fibroblast growth factor (bFGF) gene and they produce bFGF, which is apparently composed of two microheterogenous forms with Mrs of 16,500 and 17,200, respectively. bFGF derived from the rhabdomyosarcoma cells stimulates their own proliferation and that of human or bovine vascular endothelial cells. It is conceivable that the rhabdomyosarcoma-derived bFGF stimulates the growth and neovascularization of human rhabdomyosarcomas and that it may thereby contribute to the development of these tumors.

Animals↗
PubMed1986

Nucleotide sequence of a bovine clone encoding the angiogenic protein, basic fibroblast growth factor.

Basic and acidic fibroblast growth factors (FGF's) are potent mitogens for capillary endothelial cells in vitro, stimulate angiogenesis in vivo, and may participate in tissue repair. An oligonucleotide probe for bovine basic FGF was designed from the nucleotide sequence of the amino-terminal exon of bovine acidic FGF, taking into account the 55 percent amino acid sequence homology between the two factors. With this oligonucleotide probe, a full length complementary DNA for basic FGF was isolated from bovine pituitary. Basic FGF in bovine hypothalamus was shown to be encoded by a single 5.0-kilobase messenger RNA; in a human hepatoma cell line, both 4.6- and 2.2-kilobase basic FGF messenger RNA's were present. Both growth factors seem to be synthesized with short amino-terminal extensions that are not found on the isolated forms for which the amino acid sequences have been determined. Neither basic nor acidic FGF has a classic signal peptide.

Angiogenesis Inducing Agents↗
PubMed1986

The genes for basic and acidic fibroblast growth factors are on different human chromosomes.

Basic and acidic fibroblast growth factor (FGF) are related both structurally and functionally. A bovine basic FGF cDNA and a human acidic FGF genomic fragment were used as hybridization probes in Southern blot analysis of DNAs isolated from a panel of 30 mouse-human cell hybrids. The gene encoding basic FGF was assigned to human chromosome 4, and the gene for acidic FGF to human chromosome 5. The two growth factors which are presumed to have a common evolutionary ancestor are therefore not linked. A HindIII restriction fragment length polymorphism was detected for human basic FGF.

Animals↗
PubMed1986

Human basic fibroblast growth factor: nucleotide sequence and genomic organization.

Clones encoding the angiogenic endothelial cell mitogen, basic fibroblast growth factor (FGF), have been isolated from human cDNA libraries made from kidney, fetal heart, fetal liver, term placenta, and a breast carcinoma. Basic FGF cDNA clones are present in these libraries at very low levels when compared to the quantity of the growth factor in the tissues. This observation, combined with the fact that several of the clones represent unspliced transcripts, suggests that cytoplasmic basic FGF mRNA is unstable and that the protein is stored in tissues. The amino acid sequence of human basic FGF, deduced from the sequence of these cDNAs and from genomic clones, is 99% homologous to that of bovine basic FGF, implying a strong selection pressure for maintenance of function and structure. As with the bovine factor, human basic FGF does not appear to have a signal peptide sequence. Southern blot analysis of human genomic DNA and mapping of the cloned gene shows that there is only one basic FGF gene. All of the basic, heparin-binding endothelial cell mitogens of similar amino acid composition that have been described must therefore be products of this single gene.

Amino Acid Sequence↗
PubMed1983

A new technique for genetic engineering of Agrobacterium Ti plasmid.

A new technique is described that allows easy introduction of foreign genetic elements into specific regions of Agrobacterium tumefaciens DNA. It uses plasmids that (1) can be introduced, but not maintained in A. tumefaciens, (2) have a region homologous to the genome of the recipient, and (3) have an appropriate marker. Selection for the marker will yield transconjugants in which the introduced plasmid has recombined with the host genome. Applications of the technique are described.

Conjugation, Genetic↗