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At least 1,225 records · Page 68Linked to original sources
PubMed1996

Reduced germline mobility of a mariner vector containing exogenous DNA: effect of size or site?

Germline mobilization of the transposable element mariner is severely inhibited by the insertion of a 4.5- to 11.9-kb fragment of exogenous DNA into a unique SacI site approximately in the middle of the 1286-bp element. In the presence of transposase driven by the germline-specific hsp26-sgs3 promoter, mobilization of the MlwB construct (containing a 11.9-kb insertion) is detected at low frequency. Analysis of a mobilized MlwB element indicated that mobilization is mediated by the mariner transposase. However, transposed MlwB elements are also defective in germline mobilization. Rare, transposase-induced germline excision events were also recovered for such vectors. The estimated rate of excision is < 0.1% per chromosome per generation. Excision appears to be accompanied by gap repair if a suitable template is available. The data imply that the reduced mobility of mariner vectors with exogenous DNA in the SacI site results from disruption of sequences necessary for efficient mobilization. The relative stability may be a valuable property in the uses of mariner-like elements in genetic engineering of insects of economic importance.

Animals↗
PubMed2001

Clinical experiences with a new maintenance-free shock absorbing element in titanium implants.

Until now, the biokinetic elements of one implant system were to be substituted once a year in order to prevent complications of fractures of fixation screws. In this article a new implant with a maintenance-free shock absorbing element was examined. During the last 6 years, 384 dental implants with a biokinetic element (mobile-implant, SIS Inc., Klagenfurt, Austria) were placed in 138 patients. The implants were loaded with prosthetic superstructures 4 months after implantation. For comparison, 160 patients were treated with 494 conventional titanium implants of the same design without biokinetic elements. All patients were examined radiologically and clinically. Periimplant probing depth, periimplant bleeding, Periotest-values (Siemens, Bensheim, Germany) at the time of prosthetic treatment and 3, 6, 9, 12, and 24 months after implant loading were registered. Implantation was successful in 97.2% of mobile-implants and 98% of conventional implants. There was a low degree of sulcus bleeding and high degree of physiological periimplant probing depths in both patients groups. In mobile-implants, the Periotest-values were positive and similar to that of the control. There was no difference between the values in the maxilla and mandible. In the group with conventional implants, the Periotest-values were negative and showed a low degree of negativity during the first 12 months after implant loading. Periotest-values in the upper jaw were higher than in the lower jaw. There was a lower degree of periimplant bone loss after implant loading in patients with mobile-implants. In conclusion, mobile-implants demonstrate the positive effects of implants with shock absorbing elements. They are maintenance free.

Alveolar Bone Loss↗
PubMed1994

Nucleolar introns from Physarum flavicomum contain insertion elements that may explain how mobile group I introns gained their open reading frames.

Comparison of two group I intron sequences in the nucleolar genome of the myxomycete Physarum flavicomum to their homologs in the closely related Physarum polycephalum revealed insertion-like elements. One of the insertion-like elements consists of two repetitive sequence motifs of 11 and 101 bp in five and three copies, respectively. The smaller motif, which flanks the larger, resembles a target duplication and indicates a relationship to transposons or retroelements. The insertion-like elements are found in the peripheral loops of the RNA structure; the positions occupied by the ORFs of mobile nucleolar group I introns. The P. flavicomum introns are 1184 and 637 bp in size, located in the large subunit ribosomal RNA gene, and can be folded into group I intron structures at the RNA level. However, the intron 2s from both P. flavicomum and P. polycephalum contain an unusual core region that lacks the P8 segment. None of the introns are able to self-splice in vitro. Southern analysis of different isolates indicates that the introns are not optional in myxomycetes.

Animals↗
PubMed2003

Sequence, structure and expression of the hemolymph juvenile hormone binding protein gene in the tobacco hornworm, Manduca sexta.

The hemolymph juvenile hormone binding protein (hJHBP) gene of Manduca sexta is a key target of its specific ligand, juvenile hormone (JH). While the cDNA for hJHBP has been partially characterized, little is known about the hJHBP gene structure or its promoter(s) and enhancers(s). Previous studies have demonstrated that JH stimulates a rapid accumulation of hJHBP mRNA in the fat body. To better understand the underlying molecular events affecting regulation, we sequenced the M. sexta hJHBP gene and its mRNA transcript, characterized its genomic organization, and determined the spatial and temporal expression patterns of the hJHBP gene. The gene is composed of 5 exons spanning 6.7 kb. Southern blot analysis indicates that the gene is present as a single copy. The earliest expression of hJHBP occurs 24 to 48 h after fertilization. Distribution studies indicate that fat body is the only site for hJHBP expression. Elements displaying similarity with sequences of other lepidopteran genes were discovered outside the open reading frame and may represent mobile insertion elements.

Amino Acid Sequence↗
PubMed2004

Structural characterization of the dihydroflavonol 4-reductase B (DFR-B) gene in the sweet potato.

A genomic fragment containing the dihydroflavonol 4-reductase B (DFR-B) gene was cloned from the sweet potato (Ipomoea batatas) and its nucleotide sequence was analyzed. The exons and flanking regions were highly homologous to those of previously reported DFR-B genes of the Japanese morning glory, whereas the introns and the intergenic region were less conserved. In addition to the sequences of three miniature inverted-repeat transposable elements (MITEs) and one direct repeat previously reported in the DFR-B gene of Japanese morning glory, two mobile element-like sequences were newly identified in the sweet potato DFR-B gene. At least four allelic sequences were found to exist by amplification of the DFR-B gene from various sweet potato cultivars. One of these allelic sequences had a 2-kb deletion in the intergenic region and was observed in the cultivars with high anthocyanin content in their storage roots.

Alcohol Oxidoreductases↗
PubMed1997

Analysis of 36-kilodalton protein (PapA) associated with the bacteriophage particle of Bartonella henselae.

A library of Bartonella henselae DNA was screened with antibody raised to the bacteriophage particle associated with this organism. A clone was isolated that expresses a 36-kD protein (termed PapA for particle-associated protein) when examined by immunoblot analysis using antibody raised to the particle. Southern blot hybridization indicates that the gene is present on the bacterial chromosome and packaged into the 14-kb particle-associated DNA. A papA-specific probe hybridized to multiple bands of B. henselae genomic DNA digested with several different restriction endonucleases. Thus, the gene is present in multiple copies on the genome or in different arrangements within a given population of B. henselae cells. The gene coding for PapA has been sequenced and codes for a 326-amino-acid protein with a deduced molecular weight of 36,161 daltons. The deduced protein shows 33.3% identity over a 108-amino-acid sequence with the P-min gene product of Escherichia coli. P-min is partially located within the invertible P region of the excisable element e14, found on the E. coli chromosome. Taken together, these results suggest that papA is present on a mobile genetic element of the B. henselae genome and is also packaged into the bacteriophage particle.

Amino Acid Sequence↗
PubMed1999

Coordinate regulation of RAG1 and RAG2 by cell type-specific DNA elements 5' of RAG2.

RAG1 and RAG2 are essential for V(D)J recombination and lymphocyte development. These genes are thought to encode a transposase derived from a mobile genetic element that was inserted into the vertebrate genome 450 million years ago. The regulation of RAG1 and RAG2 was investigated in vivo with bacterial artificial chromosome (BAC) transgenes containing a fluorescent indicator. Coordinate expression of RAG1 and RAG2 in B and T cells was found to be regulated by distinct genetic elements found on the 5' side of the RAG2 gene. This observation suggests a mechanism by which asymmetrically disposed cis DNA elements could influence the expression of the primordial transposon and thereby capture RAGs for vertebrate evolution.

Animals↗
PubMed1999

Serial elastic elements in the damselfly wing: mobile vein joints contain resilin

Two main types of joints occur in the damselfly wing: mobile and immobile. Some longitudinal veins (RP2(-), RP3&4(-), and MP(-)) are elastically joined with cross veins, whereas other longitudinal veins (IR1(+), IR2(+), MA(+), CuA'(+)) are firmly joined with cross veins. In this study we mapped the distribution of serial elastic elements in the wing. The occurrence of resilin, a rubberlike protein, in mobile joints suggests that the automatic twisting mechanism of the leading edge by aerodynamic force works not by flexibility but by the elasticity of these joints. First, it should result in elastic energy storage in the distal areas of the wing. Second, serial elastic elements of wing presumably act as dampers of an aerodynamic force, which are responsible for gradual twisting of the leading edge.

Journal Article↗
PubMed1996

Two pathogenicity islands in uropathogenic Escherichia coli J96: cosmid cloning and sample sequencing.

Many of the virulence genes of pathogenic strains of Escherichia coli are carried in large multigene chromosomal segments called pathogenicity islands (PAIs) that are absent from normal fecal and laboratory K-12 strains of this bacterium. We are studying PAIs in order to better understand factors that govern virulence and to assess how such DNA segments are gained or lost during evolution. The isolation and sample sequencing of a set of 11 cosmid clones that cover all of one and much of a second large PAI in the uropathogenic E. coli J96 are described. These PAIs were mapped to the 64- and 94-min regions of the E. coli K-12 chromosome, which differ from the locations of three PAIs identified in other pathogenic E. coli strains. Analysis of the junction sequences with E. coli K-12-like DNAs showed that the insert at 94 min is within the 3' end of a phenylalanine tRNA gene, pheR, and is flanked by a 135-bp imperfect direct repeat. Analysis of the one junction recovered from the insert at 64 min indicated that it lies near another tRNA gene, pheV. To identify possible genes unique to these PAIs, 100 independent subclones of the cosmids were made by PstI digestion and ligation into a pBS+ plasmid and used in one-pass sample DNA sequencing from primer binding sites at the cloning site in the vector DNA. Database searches of the J96 PAI-specific sequences identified numerous instances in which the cloned DNAs shared significant sequence similarities to adhesins, toxins, and other virulence determinants of diverse pathogens. Several likely insertion sequence elements (IS100, IS630, and IS911) and conjugative R1 plasmid and P4 phage genes were also found. We propose that such mobile genetic elements may have facilitated the spread of virulence determinants within PAIs among bacteria.

Base Sequence↗
PubMed1998

Structure of genes for cecropin A and an inducible nuclear protein that binds to the promoter region of the genes from the silkworm, Bombyx mori.

Cecropins are a family of antibacterial peptide synthesized in insects as a response to bacterial infection. To study the regulation of the immune genes in insects, two cecropin A genes were cloned and sequenced from the silkworm, Bombyx mori. The two genes, CecA1 and CecA2, encoded identical preprocecropin A, having one intron of 609 bp and 929 bp, respectively. The 5'-upstream regions of the genes contained a NF-kappa B like element and IL-6-RE Type I element. Electrophoretic mobility shift assay revealed that a nuclear protein of fat body which specifically bound to the kappa B-like element was activated by injection of the larvae with peptidoglycan.

Amino Acid Sequence↗
PubMed2004

Novel type V staphylococcal cassette chromosome mec driven by a novel cassette chromosome recombinase, ccrC.

Staphylococcal cassette chromosome mec (SCCmec) is a mobile genetic element composed of the mec gene complex, which encodes methicillin resistance, and the ccr gene complex, which encodes the recombinases responsible for its mobility. The mec gene complex has been classified into four classes, and the ccr gene complex has been classified into three allotypes. Different combinations of mec gene complex classes and ccr gene complex types have so far defined four types of SCCmec elements. Now we introduce the fifth allotype of SCCmec, which was found on the chromosome of a community-acquired methicillin-resistant Staphylococcus aureus strain (strain WIS [WBG8318]) isolated in Australia. The element shared the same chromosomal integration site with the four extant types of SCCmec and the characteristic nucleotide sequences at the chromosome-SCCmec junction regions. The novel SCCmec carried mecA bracketed by IS431 (IS431-mecA-DeltamecR1-IS431), which is designated the class C2 mec gene complex; and instead of ccrA and ccrB genes, it carried a single copy of a gene homologue that encoded cassette chromosome recombinase. Since the open reading frame (ORF) was found to encode an enzyme which catalyzes the precise excision as well as site- and orientation-specific integration of the element, we designated the ORF cassette chromosome recombinase C (ccrC), and we designated the element type V SCCmec. Type V SCCmec is a small SCCmec element (28 kb) and does not carry any antibiotic resistance genes besides mecA. Unlike the extant SCCmec types, it carries a set of foreign genes encoding a restriction-modification system that might play a role in the stabilization of the element on the chromosome.

Amino Acid Sequence↗
PubMed2004

A multicomponent system is required for tetracycline-induced excision of Tn4555.

Bacteroides spp. are the predominant organisms in the intestinal tract, and they also are important opportunistic pathogens. Antibiotic therapy of Bacteroides infections often is complicated by the prevalence of drug-resistant organisms which acquire resistance genes from a variety of mobile genetic elements including conjugative transposons (CTns) and mobilizable transposons (MTns). Tn4555 is an MTn that encodes beta-lactam resistance, and it is efficiently mobilized by the Bacteroides CTns via a tetracycline (TET)-inducible mechanism. In this study a model system with CTn341 and a Tn4555 minielement was used to examine Tn4555 excision from the chromosome. Using PCR and mobilization assays it was established that excision was stimulated by TET in the presence of CTn341. In order to determine which Tn4555 genes were required for excision, int, tnpA, tnpC, xis, and mobA mutants were examined. The results indicated that int plus two additional genes, tnpC and xis, were required for optimal excision. In addition, there was no requirement for the mobA gene, as had been shown for another MTn, NBU1. The Xis protein sequence is related to a family of plasmid excisionases, but the TnpC gene product did not match anything in the sequence databases. Evidence also was obtained that suggested that Xis is involved in the control of TET-induced excision and in control of mobilization by CTn341. Overall, these results indicate that excision of MTns is a complex process that requires multiple gene products.

Bacterial Proteins↗
PubMed1997

Escape from evolutionary stasis by transposon-mediated deleterious mutations.

Evolution within a rugged fitness landscape is limited by the tendency for organisms to become trapped on local optima resulting in evolutionary stasis. It is presently unclear how founder populations escape from an adaptive peak to found a new species. Insertion sequences, transposons and other mobile DNA elements are found in all species of eukaryotes, bacteria and archaebacteria, where they have been sought and are usually considered to be genomic parasites or selfish genes. However, many transposons and other mobile repetitive DNA are remarkably species or phyla-specific, indicating that infection with transposable elements coincides with speciation events and is involved in promoting evolutionary change. We propose here a model in which transposable elements are involved in speciation events by their ability to produce irreversible deleterious mutations that promote escape from evolutionary stasis. We have constructed a genetic algorithm designed to model both spontaneous and transposon-mediated mutations in populations of asexual digital organisms. We use this model to investigate the effect of transposon-mediated mutations on the rate of evolution of digital organisms as they compete for resources within an artificial adaptive landscape. In the absence of transposon mutations the seed organisms quickly evolve to occupy the nearest adaptive peak but thereafter evolutionary stasis ensues and adjacent empty peaks are left unoccupied. In the presence of transposon mutations, evolution is again dominated by stasis but is punctuated by bursts of rapid evolution in with consecutive unoccupied adaptive peaks are filled with organisms derived from single transposition events. Rapid evolutionary events leading to founding of new biological species, may be similarly initiated by irreversible deleterious mutations induced by transposition.

Adaptation, Physiological↗
PubMed1994

An E-box/M-CAT hybrid motif and cognate binding protein(s) regulate the basal muscle-specific and cAMP-inducible expression of the rat cardiac alpha-myosin heavy chain gene.

Expression of the cardiac myosin heavy chain (MHC) genes is regulated developmentally and by numerous epigenetic factors. Here we report the identification of a cis-regulatory element and cognate nuclear binding protein(s) responsible for cAMP-induced expression of the rat cardiac alpha-MHC gene. By Northern blot analysis, we found that, in primary cultures of fetal rat heart myocytes, the elevation of intracellular levels of cAMP results in up-regulation of alpha-MHC and down-regulation of beta-MHC mRNA expression. This effect of cAMP was dependent upon the basal level of expression of both MHC transcripts and was sensitive to cycloheximide. In transient expression analysis employing a series of alpha-MHC/CAT constructs, we identified a 31-base pair fragment located in the immediate upstream region (-71 to -40), which confers both muscle-specific and cAMP-inducible expression of the gene. Within this 31-base pair fragment there are two regions, an AT-rich portion and a hybrid motif which contains overlapping sequences of E-box and M-CAT binding sites (GGCACGTGGAATG). By substitution mutation analysis, both elements were found important for the basal muscle-specific expression; however, the cAMP-inducible expression of the gene is conferred only by the E-box/M-CAT hybrid motif (EM element). Using mobility gel shift competition assay, immunoblotting, and UV-cross-linking analyses, we found that a protein binding to the EM element is indistinguishable from the transcription enhancer factor-1 (TEF-1) in terms of sequence recognition, molecular mass, and immunoreactivity. Methylation interference and point mutation analyses indicate that, besides M-CAT sequences, center CG dinucleotides of the E-box motif CACGTG are essential for protein binding to the EM element and for its functional activity. Furthermore, our data also show that, in addition to TEF-1, another HF-1a-related factor may be recognized by the alpha-MHC gene EM element. These results are first to demonstrate transcriptional activation of a sarcomeric gene by cAMP and support the role of TEF-1 and HF-1a-like factors in the regulation of alpha-MHC gene expression in cardiac myocytes.

Animals↗
PubMedDate not supplied

Group II introns and expression of conjugative transfer functions in lactic acid bacteria.

The homologous lactococcal conjugative elements pRS01 and the sex factor of Lactococcus lactis strain 712 both contain a Group II intron within a gene believed to encode a conjugative relaxase enzyme. This enzyme is responsible for nicking of DNA at the origin of transfer (oriT) sequence of the sex factor DNA to initiate the strand transfer process. Group II introns have been studied in eukaryotes, and several of these elements in yeast mitochondrial genes have received considerable attention. These introns are relatively large in size and generally encode a protein within the intron sequence. In addition to splicing activity. Group II introns are mobile genetic elements. The intron-encoded proteins (IEPs) contain endonuclease and reverse transcriptase domains believed to play an enzymatic role in genetic mobility reactions, while a putative maturase domain is thought to promote splicing by stabilizing the folding of the intron RNA into an active ribozyme structure which carries out the splicing reaction. The lactococcal introns represent the first examples of Group II introns shown to be functional in vivo in prokaryotes. Because of the advantages of a bacterial system for genetic and molecular studies, the Ll.ltrB intron from pRS01 has attracted the attention of several laboratories interested in Group II intron biology. Recently, it has been shown that the system can be adapted to function in Escherichia coli (although at somewhat reduced efficiency). In addition, it has been recently proven that the best studied form of mobility, the homing of the intron into an intronless allele of the cognate exon gene, occurs via an RNA intermediate and does not require DNA homology or generalized host recombination functions. Current efforts are analysis of the role Ll.ltrB splicing in regulating expression of pRS01 conjugation functions. The lactococcal Group II introns represent the first demonstrated genetically mobile prokaryotic retroelements, and they also have considerable potential as genetic engineering tools for Lactic Acid Bacteria (LAB) and other organisms.

Bacterial Proteins↗
PubMed2005

A large, mobile pathogenicity island confers plant pathogenicity on Streptomyces species.

Potato scab is a globally important disease caused by polyphyletic plant pathogenic Streptomyces species. Streptomyces acidiscabies, Streptomyces scabies and Streptomyces turgidiscabies possess a conserved biosynthetic pathway for the nitrated dipeptide phytotoxin thaxtomin. These pathogens also possess the nec1 gene which encodes a necrogenic protein that is an independent virulence factor. In this article we describe a large (325-660 kb) pathogenicity island (PAI) conserved among these three plant pathogenic Streptomyces species. A partial DNA sequence of this PAI revealed the thaxtomin biosynthetic pathway, nec1, a putative tomatinase gene, and many mobile genetic elements. In addition, the PAI from S. turgidiscabies contains a plant fasciation (fas) operon homologous to and colinear with the fas operon in the plant pathogen Rhodococcus fascians. The PAI was mobilized during mating from S. turgidiscabies to the non-pathogens Streptomyces coelicolor and Streptomyces diastatochromogenes on a 660 kb DNA element and integrated site-specifically into a putative integral membrane lipid kinase. Acquisition of the PAI conferred a pathogenic phenotype on S. diastatochromogenes but not on S. coelicolor. This PAI is the first to be described in a Gram-positive plant pathogenic bacterium and is responsible for the emergence of new plant pathogenic Streptomyces species in agricultural systems.

Base Sequence↗
PubMed2007

Modulation of UVB-induced and basal cyclooxygenase-2 (COX-2) expression by apigenin in mouse keratinocytes: role of USF transcription factors.

Apigenin is a bioflavonoid with chemopreventive activity against UV- or chemically-induced mouse skin tumors. To further explore the mechanism of apigenin's chemopreventive activity, we determined whether apigenin inhibited UVB-mediated induction of cyclooxygenase-2 (COX-2) expression in mouse and human keratinocytes. Apigenin suppressed the UVB-induced increase in COX-2 protein and mRNA in mouse and human keratinocyte cell lines. UVB radiation of keratinocytes transfected with a mouse COX-2 promoter/luciferase reporter plasmid resulted in a threefold increase in transcription from the promoter, and apigenin inhibited the UV-induced promoter activity at doses of 5-50 microM. Transient transfections with COX-2 promoter deletion constructs and COX-2 promoter constructs containing mutations in specific enhancer elements indicated that the effects of UVB required intact Ebox and ATF/CRE response elements. Electrophoretic mobility shift assays with supershifting antibodies were used to identify USF-1, USF-2, and CREB as proteins binding to the ATF/CRE-Ebox responsive element of the COX-2 promoter. Keratinocytes co-transfected with the COX-2 luciferase reporter and a USF-2 expression vector, alone or in combination with a USF-1 expression vector, exhibited enhanced promoter activity in both UVB-irradiated and nonirradiated cultures. However, COX-2 promoter activity was inhibited in keratinocytes co-transfected with USF-1 alone. Finally, we present data showing that the suppressive effect of apigenin on COX-2 expression could be reversed by co-expression of USF-1 and USF-2. These results suggest that one pathway by which apigenin inhibits COX-2 expression is through modulation of USF transcriptional activity.

Animals↗
PubMed2003

Group II introns: structure and catalytic versatility of large natural ribozymes.

Group II introns are large, natural catalytic RNAs or ribozymes that were discovered in organelles of certain protists, fungi, algae, and plants and more recently also in prokaryotic organisms. In vitro, some members were found to self-splice from their pre-RNAs by two consecutive transesterification reactions joining the flanking exons and releasing the intron in a typical lariat form. Apart from self-splicing, a variety of other in vitro activities have been detected for group II introns demonstrating their amazing catalytic versatility. Group II introns fold into a conserved secondary structure consisting of six domains radiating from a central wheel that brings the 5' and 3' splice junction into close proximity. Domain 1 is the largest domain that is assumed to deliver the molecular scaffold assembling the intron in its active structure, while domain 5 is the phylogenetically most conserved part that represents the active site of the ribozyme. In vivo, the splicing reaction of many, if not all group II introns is assisted by proteins either encoded by the introns themselves (maturases), or encoded by other genes of the host organisms. The host proteins known to date have additional cellular functions and seem to have been adapted for splicing during evolution. Some of the protein-encoding group II introns were also shown to act as mobile genetic elements. They can integrate efficiently into intronless alleles of the same gene (homing) and at much lower frequencies into ectopic sites (transposition). The mobility process depends on intron encoded protein functions (endonuclease and reverse transcriptase) and on the intron RNA. This review provides a comprehensive survey of the structure/function relationships and the reaction potential of group II introns, the structurally most complicated, but also most fascinating ribozymes when looking at their catalytic repertoire in vitro and in vivo.

Base Sequence↗