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At least 937 records · Page 52Linked to original sources
PubMed2005

Identification of a genomic island of Actinobacillus actinomycetemcomitans.

BACKGROUND: Horizontal gene transfer (HGT) is a process by which bacteria acquire genes from organisms of distant taxa. HGT is now recognized as a major driving force in the evolution of bacterial pathogens. Through this process, bacteria may accumulate blocks of DNA such as genomic islands (GEIs) that encode fitness or virulence factors. The periodontal pathogen A. actinomycetemcomitans has been known to exhibit variable virulence potential. It is postulated that GEIs may play a role in modifying the virulence potential of A. actinomycetemcomitans. This study was initiated to identify and determine the distribution of GEIs in A. actinomycetemcomitans. METHODS: Forty-seven A. actinomycetemcomitans strains of serotypes a through f were examined. Strain-specific variant DNA in the genomes of A. actinomycetemcomitans was identified by polymerase chain reaction (PCR) genomic mapping and sequenced to identify GEIs. The distribution of the GEIs among test strains of A. actinomycetemcomitans was determined by PCR analysis and Southern hybridization assays. RESULTS: An approximately 22 kb GEI of A. actinomycetemcomitans, designated AAI-1, was identified in five serotype b strains. The AAI-1 exhibits low %G+C and encodes proteins of phage, restriction modification systems, mobile elements, and other hypothetical proteins of unknown functions. The insertion of AAI-1 was found to cause truncation of A. actinomycetemcomitans genes at the insertion site. CONCLUSIONS: Some A. actinomycetemcomitans strains may harbor GEIs, which were acquired via HGT by the bacteria. The GEIs may increase the gene repertoire of A. actinomycetemcomitans. However, the insertion of the GEIs in A. actinomycetemcomitans may also cause truncation and inactivation of resident genes at the insertion sites. The virulence significance of such gain and loss of genes in A. actinomycetemcomitans remains to be determined.

Aggregatibacter actinomycetemcomitans↗
PubMed1995

Sequence of Asr2, a member of a gene family from Lycopersicon esculentum encoding chromosomal proteins: homology to an intron of the polygalacturonase gene.

Asr is a family of genes regulated by abscisic acid, stress and ripening in tomato. Asr2, a recently reported member of this family, has been further characterized through sequencing of a genomic clone. We report the sequencing of 2029 bp of Asr2, spanning its AT-rich (62%) upstream region with probable regulatory functions. This region displays several candidate TATA and CAAT boxes that might be involved in transcription initiation, as well as a motif similar to one previously reported to be responsible for induction by ABA. Apart from that, we found a 108-bp stretch from the 3' non-coding region which displays a high homology (92%) to a region within intron 6 of the polygalacturonase gene, which, like Asr2, is expressed in ripening tomato fruit. This striking similarity suggests the presence of either a conserved regulatory motif or an abundant mobile element.

Base Sequence↗
PubMed1998

MER53, a non-autonomous DNA transposon associated with a variety of functionally related defense genes in the human genome.

We report a new medium reiteration frequency repeat MER53 present in human and mammalian genomes. A 189 bp MER53 consensus sequence has been reconstructed based on the computer analysis of GenBank sequences. TA target site duplication and terminal inverted repeats indicate that the MER53 repeat is a non-autonomous DNA transposon related to the mariner family. Two MER53 repeats were found integrated within different mobile elements. We have found that most of the genes harboring the MER53 repeat are involved in the host defense system. The reasons for this non-random distribution of the repeat are discussed.

Animals↗
PubMed2006

The L1 retrotranspositional stimulation by particulate and soluble cadmium exposure is independent of the generation of DNA breaks.

Human exposure to toxic metals is a concern of the highest priority, due to their vast array of biological effects, including carcinogenicity. The particulate (water insoluble) form of several heavy metals presents a higher carcinogenic potential than its soluble counterparts. Our previous work demonstrates that the particulate forms of different heavy metals, such as nickel oxide, cadmium sulfide and mercury sulfide, stimulate human L1 mobile element activity leading to genomic instability. We present data demonstrating that the soluble form of CdCl2 also stimulates L1 retrotransposition in a dose-dependent manner comparable to the insoluble carcinogenic form of this compound. Reproducible results demonstrated a 2 to 3 fold dose-dependent increase in L1 retrotransposition compared to control cells. Heavy metals may cause DNA breaks through the generation of reactive oxygen species. However, evaluation of DNA damage by comet assay revealed no differences between the negative controls and the CdS-treated cells. In addition, active L1 elements express a protein with endonuclease activity that can generate toxicity through the creation of double strand breaks. To determine the contribution of the L1 endonuclease to the toxicity observed in our metal treatment assays, we compared the wildtype L1 vector with an L1 endonuclease-mutant vector. The presence of an active L1 endonuclease did not contribute significantly to the toxicity observed in any of the CdCl2 or CdS doses evaluated. No correlation between the creation of DNA breaks and L1 activity was observed. Alternatively, heavy metals inhibit enzymatic reactions by displacement of cofactors such as Zn and Mg from enzymes. Concomitant treatment with Mg(Ac)2 and Zn(Ac)2 ppb suppresses the stimulatory effect on L1 activity induced by the 3.8 ppb CdS treatment. Overall, these results are consistent with our previous observations, suggesting that the mechanism of L1 stimulation by heavy metals is most likely due to an overall inhibition of DNA repair proteins or other enzymes caused by the displacement of Mg and Zn from cellular proteins.

Cadmium Chloride↗
PubMed1998

The Knights of the Round Table hypothesis of tumour suppressor gene function--noble sacrifice or sexual dalliance: genes, including p53, BRCA1/2 and RB have evolved by horizontal and vertical transmission of mating factor genes and are involved in gametogenesis, implantation, development and tumourigenesis.

The genes involved in negative cell cycle regulation and familial tumour susceptibility including APC, BRCA, p53, RB, WT1 are unique and have no homologies with other genes. Our hypothesis suggests they originated from mating factor genes, which halted cell division in response to stress to generate genetic diversity by sexual mechanisms. Some have evolved principally by vertical transmission (mismatch repair), others by horizontal transmission via mobile elements, predominantly in oocytes. We demonstrate amplification in human extra-embryonic tissues in fetus and mother in implantation; in the developing fetus, differing tissue-specific patterns are seen, especially between testis and ovary. We suggest that the fetus is susceptible to maternal transmission of infections including CMV, malaria, trypanosomes, whose sequences occur within these genes. In head and neck cancers, we demonstrate specific patterns of loss or instability involving up to seven different TSG. We suggest mechanisms of tumourigenesis involve transposable elements and episome formation, leading to loss of negative cell cycle regulation and exit from G0.

Animals↗
PubMed1976

[Malfunction of the Smeloff-Cutter mitral prosthesis: echo-phonocardiographic diagnosis in two successfully re-operated cases (author's transl)].

Five cases of Smeloff-Cutter prosthesis implanted in the mitral position nine years ago were investigated with combined echocardiographic and phonocardiographic recordings. In two cases a malfunction was demonstrated and a surgical confirmation was obtained at the reoperation. Normal and abnormal echocardiographic patterns of the Smeloff-Cutter prosthesis are reported and discussed. The Authors stress the importance of combined echo-phono recordings when malfunction of the mobile element of a mechanical prosthesis is suspected.

Adult↗
PubMed1999

beta-Lactamases of increasing clinical importance.

Resistance to b-lactam-containing antimicrobial agents continues to increase, frequently due to the presence of b-lactamases in Gram-negative bacteria. Over the past twenty-five years broad-spectrum enzymes such as TEM- and SHV-variants and the metallo-b-lactamases have become more prolific. As a result of the ability of plasmids to continue to acquire additional resistance determinants, many of the b-lactamase-producing Gram-negative pathogens have become multi-drug resistant. In combination with decreased permeability, the organisms can become virtually untreatable with current therapies. The major groups of b-lactamases that pose the most serious therapeutic problems include the extended-spectrum b-lactamases, the plasmid-mediated cephalosporinases, the inhibitor-resistant TEM- or SHV-derived b-lactamases and the carbapenem-hydrolyzing b-lactamases. Those enzymes that can be transferred on mobile elements are the most serious of the newer b-lactamases, and include enzymes in each of the four groups outlined above.

Anti-Bacterial Agents↗
PubMed1999

[The role of genome repetitive sequences in primary hypertension].

Genetic determining factors of essential hypertension seems to involve a dynamic mutation or a similar process. The mobile elements of the genome: moderately recurrent sequences, play a special role in initiation of such a process. A possible molecular mechanism of the initiation and development of the dynamic mutation, is described.

Animals↗
PubMedDate not supplied

[Comparative analysis of the life span in HA and BA Drosophila melanogaster].

We studied lifespan (LS) of Drosophila melanogaster strains HA and BA. The first one was generated by long-term selection for low male sexual activity and features decreased LS as well as the changes in a relatively constant index--coefficient of LS variation. The BA strain was derived from the HA strain by reverse selection and has the mean LS and coefficient of LS variation similar to those of the normal strain D-32. Analysis of the death curves of the HA strain insects does not exclude existence of a subpopulation with the normal LS within these strain. The obtained data are discussed in the context of possible involvement of mobile element transposition in animal LS control.

Animals↗
PubMedDate not supplied

[The role of integrons in dissemination of antibiotic resistance].

Bacteria can transfer genetic information to get protection against most antibiotics. The acquisition of resistance genes involves genetic mobile elements such as plasmids and transposons. Another genetic structures, named integrons, have been described and contain one or more gene cassettes located at a specific site. Integrons contain an intI gene encoding a site-specific recombinase belonging to the integrase family and a recombination site attI. A gene cassette includes an open reading frame and, at the 3'-end, a recombination site attC. Integration or excision of cassettes occurs by a site-specific recombination mechanism catalyzed by the integrase. However, insertion can rarely occur, at non-specific sites leading to a stable situation for the cassette. Cassettes are transcribed from a common promoter located in the 5'-conserved segment and expression of distal genes is reduced by the presence of upstream cassettes. Most gene cassettes encode antibiotic resistant determinants but antiseptic resistant genes have also been described. Integrons seem to have a major role in the spread of multidrug resistance in Gram-negative bacteria but integrons in Gram-positive bacteria have been recently described. Moreover, the finding of super-integrons with gene cassettes coding for other determinants (biochemical functions, virulence factors) in different Gram negative bacteria suggests that integrons are probably implied in bacterial genome evolution.

Anti-Bacterial Agents↗
PubMed2000

[Presence of conjugative transposon Tn1545 in strains of Streptococcus pneumoniae with mef(A), erm(B), tet(M), catpC194 and aph3'-III genes].

We studied the association of MLS resistance genes (erm(B) and mef(A) with others non-MLS resistance genes: tet(M) (tetracycline and minocycline), catpC194 (chloramphenicol) and aph3'-III (kanamycin) in order to know how is selected the multiresistant in Streptococcus pneumoniae. The tet(M) and catpC194 genes were present very often in the pneumococci with the erm(B) gene but the aph3'-III was found only in four strains. Tn1545 was nearly always the responsible for the dissemination of these genes. In contrast, mef(A) was not associated with tet(M) and and catpC194 and is disseminated in a different conjugative transposon. The linkage of multiple antibiotic resistance genes on the same mobile element is of importance for public health, because the use of one antibiotic selects for the transposon which carries multidrug resistance genes.

Anti-Bacterial Agents↗
PubMedDate not supplied

[Organization of extended repeats in heterochromatin in sex chromosomes in the common vole species Microtus group "arvalis"].

Two long repeats, MS3 and MS4, are predominantly located in sex-chromosomal heterochromatin in common vole species. Their tandem arrangement was revealed by means of the PCR analysis of genomic DNAs of four Microtus species and by restriction mapping of clones selected from a M. rossiaemeridionalis genomic library. Several mobile elements proved incorporated in a monomeric unit of each repeat and amplified together with its other components. In addition, LINE inserts were found in MS4 tandem arrays. The copy number of both repeats per haploid genome was estimated at 100-300 for euchromatin and 20,000-40,000 for the M. rossiaemeridionalis genome. The repeats were assumed to be the major component of sex-chromosomal heterochromatin DNA.

Animals↗
PubMed2001

[Thrombotic or embolic stroke?].

BACKGROUND: Transoesophageal echocardiography reveals a possible source of embolism in many patients who present with acute brain ischaemia. The aim of this study was to observe the prevalence of possible sources of embolism in a representative Norwegian stroke population in a county hospital with a defined reference population. METHODS: All 103 patients with ischaemic stroke or transient ischaemic attack admitted to our hospital during a five-month period were enrolled. We performed transthoracic echocardiography in 98 patients, transoesophageal echocardiography in 83, and Doppler examination of the precerebral arteries in 92. RESULTS: Mean patient age was 72 years; 19 patients had atrial fibrillation. Examinations revealed 70 potential sources of embolism in 55 patients. Twenty-eight findings were in the heart. Five patients had thrombi in left-sided heart chambers. Ten patients had patent foramen ovale; 11 had atrial septal aneurysm; four had both. Thirty-three had atheromas of the aorta with a protrusion of more than 4 mm, ten of them with mobile elements. Nine patients had carotid stenosis of high grade or carotid occlusion ipsilateral to a hemispheric stroke. INTERPRETATION: Potential precerebral sources of embolism are common in a representative population of patients with ischaemic stroke. Atheromas of the aorta may be an important contributor to brain ischaemia.

Aged↗
PubMed2001

The detection, cloning, and characterisation of WIS 2-1A retrotransposon-like sequences in Triticum aestivum L. and xTriticosecale Wittmack and an examination of their evolution in related Triticeae.

Retrotransposons and other mobile elements are major components of the repeated DNA fraction in higher-plant genomes. They have undoubtedly played an important role in higher plant genome evolution. The present work details the detection and characterisation of a WIS 2-1A related sequence in direct wheat relatives, and discusses the prevalence and evolution of its copy number in their genomes. An increase in copy number is detected when following the natural hybridisation processes that gave rise to bread and durum wheats. However, the opposite is observed in the development of triticale, a synthetic hybrid.

Base Sequence↗
PubMedDate not supplied

[Gram-positive bacterial infections resistant to antibiotic treatment].

Antibiotic resistance has become a major problem in the treatment of gram-positive bacterial infections. These organisms are able to escape antibiotic activity through several mechanisms including beta-lactamase production, altered penicillin-binding proteins, aminoglycoside-modifying enzymes, modification of the target site of the antibiotic, and active efflux. Resistant determinants may be carried on the chromosome, and are transmitted vertically by clonal dissemination, or on mobile elements such as plasmids, transposons or integrons capable of horizontal transfer both within and between species. Several resistant genes can be inserted in a given integron, resulting in multi-drug resistance. Antimicrobial resistance mechanisms can be caused or induced following the widespread use of antibiotics. The most important gram-positive resistant organisms include penicillin-resistant Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci, methicillin-resistant Staphylococcus aureus with intermediate resistance to vancomycin, and enterococcal strains that express high-level resistance to aminoglycosides and/or resistance to vancomycin. In several instances, these strains show multi-drug resistance and cannot be treated with currently available agents. Therapeutic strategies include the use of a higher antibiotic dosage, the use of alternative, non-conventional drugs, alone or in combination, after demonstration of their efficacy in vitro and in experimental animal models, and the development of new drugs. New agents available include quinupristin/dalfopristin and line-zolid with activity against most resistant gram-positive bacteria. Promising new drugs that may reach the market in the near future include daptomycin and oritavancin. Careful use of antibiotics and adherence to infection control standards are crucial in preventing the development and the spread of resistant organisms.

Drug Resistance, Microbial↗
PubMedDate not supplied

[Role of double-stranded RNA in eukaryotic gene silencing].

Data on RNA interference, that is, posttranscriptional gene silencing by homologous double-stranded (ds) RNA, are reviewed. Gene silencing caused by exogenous dsRNA in artificial systems and observed in transgenic organisms carrying additional gene copies is considered. Data are summarized on the mechanism that arose during evolution of the Drosophila melanogaster genome to suppress repetitive genes with the use of dsRNA and thereby to prevent male sterility. The role of dsRNA in inhibiting expression and transposition of mobile elements is discussed on the basis of authors own and published findings.

Animals↗
PubMed1975

The different migratory characteristics of lymphocyte populations from a whole spleen transplant.

Spleens from AS x BN donor rats labelled in vivo by multiple doses of [3H]thymidine were transplanted into syngeneic recipients by anastomosis to the abdominal great vessels. The recipients were killed 1-5 days after receiving the whole spleen transplants and the numbers and location of the [3H]thymidine-labelled cells which had migrated from the labelled donor spleen traced by means of autoradiographs of sections, imprints and smears of various recipient lymphoid tissues. These results were compared with the migration pattern of labelled dissociated spleen cell suspensions injected intravenously. The latter consists almost entirely of small lymphocytes which migrate to T or B areas of recipient spleen, lymph nodes and Peyer's patches. The labelled whole spleens also contained cells which migrated to the T and B areas of recipient lymphoid tissues, but in addition contained many lymphoid cells which migrated to the red pulp of the recipient spleen and to the lamina propria of the gut. These experiments showed, therefore, that the spleen contains mobile elements which have not been detected by transfer of spleen cell suspensions.

Animals↗
PubMed2002

[The relationship between ontogenesis and phylogeny in the light of genetics: the problem of macro mutations (morphological and molecular aspects)].

An original hypothesis of the molecular genetic basis of evolution is considered. Evolutionary events were assumed to result from a temporal discordance in the interaction between tissue anlages in the course of individual development. The discordance may be caused by satellite DNA rearrangement by macromutations associated with mobile element insertion in the genome.

Animals↗