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Dictyostelium discoideum plasmid Ddp2 from the wild strain WS380B is a 5.8-kilobase (kb) supercoiled circle with a copy number of 300 per haploid genome. We previously described the construction of an extrachromosomally replicating transformation vector pnDeI carrying 4.7 kb of Ddp2 sequences (B. Leiting, and A. Noegel, Plasmid 20:241-248, 1988). In order to reduce the sequences required for extrachromosomal maintenance in D. discoideum, we characterized Ddp2 by sequence analysis, by deletion experiments, by transcription mapping, by electrophoretic mobility shift assays, and by expression of its single open reading frame in Escherichia coli. Two elements were involved in replication of Ddp2: a cis-acting sequence located on a 592-base-pair (bp) fragment that consisted of 220 bp of essential and 372 bp of auxiliary sequences, and a 2.7-kb open reading frame which most likely encodes a trans-acting factor. The cis- and trans-acting elements did not overlap and were shown to act independently from the location of the sequences encoding the trans-acting factor.
Mol Cell Biol 1990 Jul
PMID:The extrachromosomal replication of Dictyostelium plasmid Ddp2 requires a cis-acting element and a plasmid-encoded trans-acting factor. 219 61

This paper has two purposes. The first is to review the past studies on the structure, biosynthesis, and immunological properties of a class of glycoproteins, the lysosomal enzymes, in Dictyostelium discoideum. The second purpose is to present new data on the analysis of mutant strains altered in the biosynthesis of the lipid-linked precursor of N-linked oligosaccharides, and on the characterization of new carbohydrate antigenic determinants found on multiple proteins in Dictyostelium. We will also show how a combination of genetic, biochemical and immunochemical approaches have been used to unravel a portion of the glycosylation pathway in Dictyostelium. The long-term goal of these studies is to use Dictyostelium discoideum as a model system to understand the functions of a variety of glycoconjugates in a multicellular organism. The existence of a large number of mutant strains which are altered in a variety of cellular functions, development and the posttranslational modification of multiple proteins, offers a great opportunity to explore this area.
Mol Cell Biochem
PMID:Modifications of lysosomal enzymes in Dictyostelium discoideum. 243 32

We used an antibody specific for Dictyostelium discoideum myosin to screen a lambda gt11 cDNA expression library to obtain cDNA clones which encode the Dictyostelium essential myosin light chain (EMLC). The amino acid sequence predicted from the sequence of the cDNA clone showed 31.5% identity with the amino acid sequence of the chicken EMLC. Comparisons of the Dictyostelium EMLC, a nonmuscle cell type, with EMLC sequences from similar MLCs of skeletal- and smooth-muscle origin, showed distinct regions of homology. Much of the observed homology was localized to regions corresponding to consensus Ca2+-binding of E-F hand domains. Southern blot analysis suggested that the Dictyostelium genome contains a single gene encoding the EMLC. Examination of the pattern of EMLC mRNA expression showed that a significant increase in EMLC message levels occurred during the first few hours of development, coinciding with increased actin expression and immediately preceding the period of maximal chemotactic activity.
Mol Cell Biol 1988 Feb
PMID:Dictyostelium discoideum myosin: isolation and characterization of cDNAs encoding the essential light chain. 245 Nov 26

A Dictyostelium discoideum repetitive element composed of long repeats of the codon (AAC) is found in developmentally regulated transcripts. The concentration of (AAC) sequences is low in mRNA from dormant spores and growing cells and increases markedly during spore germination and multicellular development. The sequence hybridizes to many different sized Dictyostelium DNA restriction fragments indicating that it is scattered throughout the genome. Four cDNA clones isolated contain (AAC) sequences in the deduced coding region. Interestingly, the (AAC)-rich sequences are present in all three reading frames in the deduced proteins, i.e., AAC (asparagine), ACA (threonine) and CAA (glutamine). Three of the clones contain only one of these in-frame so that the individual proteins carry either asparagine, threonine, or glutamine clusters, not mixtures. However, one clone is both glutamine- and asparagine-rich. The (AAC) portion of the transcripts are reiterated 300 times in the haploid genome while the other portions of the cDNAs represent single copy genes, whose sequences show no similarity other than the (AAC) repeats. The repeated sequence is similar to the opa or M sequence found in Drosophila melanogaster notch and homeo box genes and in fly developmentally regulated transcripts. The transcripts are present on polysomes suggesting that they are translated. Although the function of these repeats is unknown, long amino acid repeats are a characteristic feature of extracellular proteins of lower eukaryotes.
Mol Gen Genet 1989 Sep
PMID:Nucleotide sequences of Dictyostelium discoideum developmentally regulated cDNAs rich in (AAC) imply proteins that contain clusters of asparagine, glutamine, or threonine. 251 21

We have constructed an expression cartridge which has the bacterial hygromycin resistance gene (hph) fused to the Dictyostelium discoideum actin 15 promoter, with a segment of 3'-flanking DNA from the actin 15 locus placed downstream of the hph gene to serve as a transcription terminator. The plasmid pDE109, which contained this cartridge and a Dictyostelium origin of replication, transformed D. discoideum with high efficiency under hygromycin selection. The availability of this selectable marker circumvents the previous limitation of having G418 resistance as the only selectable marker for this organism; secondary transformation can now be used to introduce DNA into previously transformed cell lines.
Mol Cell Biol 1989 May
PMID:Hygromycin resistance as a selectable marker in Dictyostelium discoideum. 254 56

The DNA sequences involved in transcription control by a cAMP-dependent mechanism have been localized in the thyroglobulin gene promoter region by a functional assay. The proximal 5'-flanking sequences from the bovine thyroglobulin gene were linked to the bacterial chloramphenicol acetyl-transferase gene. Transient expression of this reporter gene was studied in dog thyrocytes in primary culture in the presence, or absence, of cAMP stimulation. Deletion analysis showed that the cAMP-responsive region is contained within the first 250 base-pairs of the promoter, and suggests that it could correspond to a sequence conserved between species. These DNA sequences do not bear significant homology with cAMP-responsive elements (CRE) described previously. By contrast, some similarities were found with the fat-specific element (FSE2) of genes under cAMP control in adipocytes and with DNA elements mediating cAMP-dependent regulation of expression of two different genes in the lower eukaryote Dictyostelium discoideum. This suggests that control of Tg gene transcription by cAMP could involve a mechanism different from the one mediated by a classical CRE.
Mol Cell Endocrinol 1989 Jun
PMID:Identification of a cAMP-responsive region in thyroglobulin gene promoter. 254 76

Phosphorylation of the regulatory light chains (RMLC) of nonmuscle myosin can increase the actin-activated ATPase activity and filament formation. Little is known about these regulatory mechanisms and how the RMLC are involved in ATP hydrolysis. To better characterize the nonmuscle RMLC, we isolated cDNAs encoding the Dictyostelium RMLC. Using an antibody specific for the RMLC, we screened a lambda gt11 expression library and obtained a 200-base-pair clone that encoded a portion of the RMLC. The remainder of the sequence was obtained from two clones identified by DNA hybridization, using the 200-base-pair cDNA. The composite RMLC cDNA was 645 nucleotides long. It contained 60 base pairs of 5' untranslated, 483 bases of coding, and 102 base pairs of 3' untranslated sequence. The amino acid sequence predicted an 18,300-dalton protein that shares 42% amino acid identity with Dictyostelium calmodulin and 30% identity with the chicken skeletal myosin RMLC. This sequence contained three regions that were similar to the E-F hand calcium-binding domains found in calmodulin, troponin C, and other myosin light chains. A sequence similar to the phosphorylation sequence found in chicken gizzard and skeletal myosin light chains was found at the amino terminus. Genomic Southern blot analysis suggested that the Dictyostelium genome contains a single gene encoding the RMLC. Analysis of RMLC expression patterns during Dictyostelium development indicated that accumulation of this mRNA increases just before aggregation and again during culmination. This pattern is similar to that obtained for the Dictyostelium essential myosin light chain and suggests that expression of the two light chains is coordinated during development.
Mol Cell Biol 1989 Jul
PMID:Dictyostelium discoideum myosin: isolation and characterization of cDNAs encoding the regulatory light chain. 255 Jul 95

We have characterized a cDNA and the corresponding gene for a cyclic AMP-inducible gene expressed during Dictyostelium development. This gene, BP74, was found to be first expressed about the time of aggregate formation, approximately 6 h after starvation. Accumulation of BP74 mRNA did not occur in Dictyostelium cells that had been starved in fast-shaken suspension cultures but was induced in similar cultures to which cyclic AMP pulses had been added. The BP74 cDNA and gene were characterized by DNA sequence analysis and transcriptional mapping. When the BP74 promoter region was fused with a chloramphenicol acetyltransferase reporter gene and reintroduced into Dictyostelium cells, the transfected chloramphenicol acetyltransferase gene displayed the same developmentally regulated pattern of expression as did the endogenous BP74 gene, suggesting that all of the cis-acting elements required for regulated expression were carried by a 2-kilobase cloned genomic fragment. On the basis of sequence analysis, the gene appeared to encode a protein containing a 20-residue hydrophobic sequence at the amino-terminal end and 26 copies of a 20-amino-acid repeat.
Mol Cell Biol 1989 Oct
PMID:Expression and organization of BP74, a cyclic AMP-regulated gene expressed during Dictyostelium discoideum development. 255 85

The signal transduction pathways that lead to gene induction are being intensively investigated in Dictyostelium discoideum. We have identified by deletion and transformation analysis a sequence element necessary for induction of a gene coding for uridine diphosphoglucose pyrophosphorylase (UDPGP1) of D. discoideum in response to extracellular cyclic AMP (cAMP). This regulatory element is located 380 base pairs upstream of the transcription start site and contains a G+C-rich partially palindromic sequence. It is not required for transcription per se but is required for induction of the gene in response to the stimulus of extracellular cAMP. The cAMP response sequence is also required for induction of the gene during normal development. A second A+T-rich cis-acting region located immediately downstream of the cAMP response sequence appears to be essential for the basal level of expression of the UDPGP1 gene. The position of the cAMP response element coincides with a DNase I-hypersensitive site that is observed when the UDPGP1 gene is actively transcribed.
Mol Cell Biol 1989 Nov
PMID:Identification of a signal transduction response sequence element necessary for induction of a Dictyostelium discoideum gene by extracellular cyclic AMP. 255 38

A mutation (mhcA1 in strain HMM) created by insertional gene inactivation was used to map the Dictyostelium discoideum myosin heavy chain gene (mhcA) to linkage group IV. Three phenotypic traits associated with this mutation (slow colony growth, inability of the mutant to develop past aggregation, and the presence of five to ten integrated vector copies) cosegregated as expected for the consequences of a single insertional event. This linkage was confirmed using a restriction fragment length polymorphism. The mhcA1 mutation was recessive to wild type and was nonallelic with mutations at the following loci on linkage group IV: aggJ, aggL. couH, minA, phgB and tsgB. This work demonstrates the ability to apply standard techniques developed for D. discoideum parasexual genetic analyses to mutants generated by transformation, which is of particular relevance to analysis of genes for which no classical mutations or restriction fragment length polymorphisms are available.
Mol Gen Genet 1989 Apr
PMID:Linkage analysis of the myosin heavy chain gene in Dictyostelium discoideum using a mutation generated by homologous recombination. 256 78


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