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At least 973 records · Page 54Linked to original sources
PubMed2004

Analyses of P-like transposable element sequences from the genome of Anopheles gambiae.

We have identified 50 P element-homologous sequences in the genome of Anopheles gambiae by performing homology searches against the public genome database of A. gambiae using the canonical P element from Drosophila melanogaster as a query sequence. While most of these sequences belong to P subfamilies previously described from anopheline mosquitoes, at least four new subfamilies were identified. One of these A. gambiae P elements, which we termed AgPLS, was analysed in detail. AgPLS consists of three exons and does not have inverted terminal repeats. This element retains several of the structural features of other P-encoded peptides, such as motifs involved in DNA-protein and protein-protein interaction, and a motif involved in GTP utilization. Strong sequence and structural similarity to functional P elements, a number of nonsynonymous substitutions that is smaller than that of synonymous substitutions and the presence of putative nuclear localization signals suggest that the A. gambiae elements may retain the capacity for transposition or its repression. These sequences seem to be most closely related to P elements described from Musca domestica and Lucilia cuprina, the only P element hosts known outside the family Drosophilidae.

Amino Acid Sequence↗
PubMed1982

Movement of yeast transposable elements by gene conversion.

We have constructed yeast strains in which Ty (transposon yeast) elements at the HIS4 locus are genetically marked with the yeast URA3 gene. By isolating and analyzing Ura- derivatives of these strains, we have detected a variety of Ty-mediated recombination events. In this paper, we describe events in which the DNA sequence of the Ty element at the HIS4 locus is replaced by the DNA sequence of a different Ty element. These replacements occur without alterations in the flanking DNA sequence and without chromosomal aberrations. We believe that these events result from gene conversion between the Ty element at HIS4 and a Ty element at a different site in the yeast genome. Gene conversion can occur between Ty elements that differ by large insertion and substitution mutations. These recombination events result not only in the movement of Ty sequences but also in alterations in expression of the adjacent HIS4 gene. Different Ty elements at the same site in the HIS4 regulatory region can result in His-, His+, and cold-sensitive His+ phenotypes. Several Ty elements render expression of the HIS4 gene subject to control by genes at the mating type locus.

DNA Restriction Enzymes↗
PubMed1985

Transposable element sequences involved in the enhancement of yeast gene expression.

The his4-917 mutation of yeast results from the insertion of a Ty element, Ty917, into the 5' regulatory region of the HIS4 gene. Ty917 prevents HIS4 transcription, thus rendering the cell histidine requiring. Recombination between Ty917 and a Ty element elsewhere in the yeast genome can result in the replacement of part or all of the Ty917 element by sequences from the Ty element. Recombinant derivatives display a variety of phenotypes including His-, weakly His+, and strongly His+. In most of the His+ derivatives, the expression of HIS4 is controlled by genes at the mating type locus. To identify the Ty sequences important in controlling the expression of an adjacent gene, we used Ty elements that have different effects on gene expression to construct hybrid Ty elements in vitro. The effects of these hybrid elements on HIS4 expression were examined. These experiments indicate that the critical sequence differences between Ty elements that permit HIS4 expression and those that prevent its expression lie in the rightmost (HIS4-proximal) 730 base pairs of the element. The DNA sequence of this region was determined for three elements: Ty917, which prevents HIS4 expression; Ty917(467), which confers a weak His+ phenotype; and Ty917(480), which confers a strong His+ phenotype. Within this region, Ty917(467) differs from Ty917 by a single base-pair change that is in the internal (epsilon) region of the Ty element. Ty917(480) differs from Ty917 by this same base-pair change and by 10 changes in the terminal delta sequence. The sequence change common to Ty917(467) and Ty917(480) lies in a region of the Ty element that is homologous to the simian virus 40 enhancer of transcription.

Base Sequence↗
PubMed1988

The Ds1 transposable element acts as an intron in the mutant allele Adh1-Fm335 and is spliced from the message.

The Ds-induced maize Adh1 allele Adh1-Fm335 retains its anaerobic regulation and normal transcription start site despite the presence of the 405 bp Ds element in the 5' untranslated leader region of the gene. The steady state level of Adh1-specific transcript is reduced to about 1% that of the progenitor or revertant alleles. Run-on transcription studies show that the reduced level of Adh1 specific mRNA is not attributable to a decreased transcription rate. S1 mapping indicates that the Ds element is spliced from the Adh1-Fm335 transcript using a donor site 14 bp into the Ds element and an acceptor site at the 3' junction of the Ds element with the flanking genome DNA.

Alcohol Dehydrogenase↗
PubMed1988

Molecular mechanisms in the developmental regulation of the maize Suppressor-mutator transposable element.

The maize Suppressor-mutator (Spm) element can exist in one of three heritable forms: (1) a stably active form, (2) a stably inactive form, termed cryptic, and (3) a labile form, here termed programmable, in which the element exhibits one of a variety of heritable developmental programs of expression. Active elements are transcribed and are hypomethylated at sites upstream of the transcription start site, whereas inactive elements are transcriptionally silent and largely methylated at the upstream sites. Active (both stable and programmable), inactive programmable, and cryptic elements are unmethylated, partially methylated, and fully methylated, respectively, at sites within an 0.35-kb 80% G + C region just downstream from the transcription start site. An active Spm element in a genome with a cryptic element promotes its partial demethylation but not its transcriptional activation. In contrast, a trans-acting Spm promotes extensive demethylation and transcriptional activation of an inactive programmable element, as well as its heritable reactivation. These observations define the molecular components of the Spm element's developmental regulatory mechanism. We discuss their general relevance to the developmental regulation of gene expression.

DNA Probes↗
PubMed1998

Novel sequence organization and insertion specificity of IS605 and IS606: chimaeric transposable elements of Helicobacter pylori.

IS605, an insertion sequence (IS) that is unusual in containing homologs of genes for the single putative transposases of two other unrelated IS elements (IS200 and IS1341), was found in nearly one-third of a set of 238 independent isolates of the gastric pathogen Helicobacter pylori. Hybridization and PCR tests indicated that any strain carrying one of these ORFs also carried the other, which implies that both ORFs are in the same unit of transposition. The IS605 ends and target sites for insertion were identified by sequencing eight preexisting insertions in strain NCTC11638, corresponding empty sites in other strains, and new transpositions in E. coli of an IS605 derivative marked with a selectable chloramphenicol-resistance gene. These tests showed that IS605 is also unusual in: (1) having unique, not inverted repeat, ends; (2) not duplicating (or deleting) target sequences during transposition; and (3) inserting with its left (IS200-homolog) end next to 5'-TTTAA or 5'-TTTAAC. IS605 was implicated in at least two genome rearrangements in strain NCTC11638. A second member of the IS605 family, called IS606 (25% amino acid identity to IS605 in inferred proteins) was found in one-third of 38 H. pylori strains tested, many of which did not carry IS605. The features of these two chimaeric IS elements are discussed in terms of possible transposition mechanisms, IS element evolution, and effects of IS elements on genome organization and evolution in the microbes that they inhabit.

Base Sequence↗
PubMed1988

Analysis of yeast chromosomal regions carrying members of the glutamate tRNA gene family: various transposable elements are associated with them.

We carried out an analysis on the genomic organisation of the tRNA(Glu) family in S. cerevisiae; eight clones were characterized by restriction mapping, hybridization and sequencing. These data taken together with our earlier findings show that the individual tRNA(Glu3) copies are identical only in their structural part but embedded in entirely different genomic environments. All of the tRNA genes identified here are flanked by elements such as Ty, delta, sigma, and tau. In some cases, sequences from different elements form complex patterns indicating a sophisticated history of these chromosomal regions. A novel observation is that Ty and delta in the regions analyzed are exclusively associated with the tRNA genes. The observed patterns imply that the tRNA genes mark regions of multiple transposition and subsequent excision events, but that these have occurred after the individual tRNA gene copies had been fixed in their present locations. Transcription experiments by the use of micro-injection into Xenopus oocytes suggest that the elements flanking the tRNA genes exert a modulating effect on their expression.

Animals↗
PubMed1995

Molecular evolution of P transposable elements in the genus Drosophila. I. The saltans and willistoni species groups.

A phylogenetic survey using the polymerase chain reaction (PCR) has identified four major P element subfamilies in the saltans and willistoni species groups of Drosophila. One subfamily, containing about half of the sequences studied, consists of elements that are very similar to the canonical (and active) P element from D. melanogaster. Within this subfamily, nucleotide sequence differentiation among different copies from the same species and among elements from different species is relatively low. This observation suggests that the canonical elements are relatively recent additions to the genome or, less likely, are evolving slowly relative to the other subfamilies. Elements belonging to the three noncanonical lineages are distinct from the canonical elements and from one another. Furthermore, there is considerably more sequence variation, on the average, within the noncanonical subfamilies compared to the canonical elements. Horizontal transfer and the coexistence of multiple, independently evolving element subfamilies in the same genome may explain the distribution of P elements in the saltans and willistoni species groups. Such explanations are not mutually exclusive, and each may be involved to varying degrees in the maintenance of P elements in natural populations of Drosophila.

Animals↗
PubMed1991

Isolation of an active human transposable element.

Two de novo insertions of truncated L1 elements into the factor VIII gene on the X chromosome have been identified that produced hemophilia A. A full-length L1 element that is the likely progenitor of one of these insertions was isolated by its sequence identity to the factor VIII insertion. This L1 element contains two open-reading frames and is one of at least four alleles of a locus on chromosome 22 that has been occupied by an L1 element for at least 6 million years.

Alleles↗
PubMed1990

Evidence for horizontal transmission of the P transposable element between Drosophila species.

Several studies have suggested that P elements have rapidly spread through natural populations of Drosophila melanogaster within the last four decades. This observation, together with the observation that P elements are absent in the other species of the melanogaster subgroup, has lead to the suggestion that P elements may have entered the D. melanogaster genome by horizontal transmission from some more distantly related species. In an effort to identify the potential donor in the horizontal transfer event, we have undertaken an extensive survey of the genus Drosophila using Southern blot analysis. The results showed that P-homologous sequences are essentially confined to the subgenus Sophophora. The strongest P hybridization occurs in species from the closely related willistoni group. A wild-derived strain of D. willistoni was subsequently selected for a more comprehensive molecular examination. As part of the analysis, a complete P element was cloned and sequenced from this line. Its nucleotide sequence was found to be identical to the D. melanogaster canonical P, with the exception of a single base substitution at position 32. When the cloned element was injected into D. melanogaster embryos, it was able to both promote transposition of a coinjected marked transposon and induce singed-weak mutability, thus demonstrating its ability to function as an autonomous element. The results of this study suggest that D. willistoni may have served as the donor species in the horizontal transfer of P elements to D. melanogaster.

Animals↗
PubMed1985

Novel one-step cloning vector with a transposable element: application to the Myxococcus xanthus genome.

A new strategy was developed for rapid cloning of genes with a transposon mutation library. We constructed a transposon designated TnV that was derived from Tn5 and consists of the gene coding for neomycin phosphotransferase II as well as the replication origin of an Escherichia coli plasmid, pSC101, flanked by Tn5 inverted repeats (IS50L and IS50R). TnV can transpose to many different sites of DNA in E. coli and Myxococcus xanthus and confers kanamycin resistance (Kmr) to the cells. From the Kmr cells, one-step cloning of a gene which is mutated as a result of TnV insertion can be achieved as follows. Chromosomal DNA isolated from TnV-mutagenized cells is digested with an appropriate restriction enzyme, ligated, and transformed into E. coli cells with selection for Kmr. The plasmids isolated contain TnV in the target gene. The plasmid DNA can then be used as a probe for characterization of the gene and screening of clones from a genomic library. We used this vector to clone DNA fragments containing genes involved in the development of M. xanthus.

Cloning, Molecular↗
PubMed1992

Intragenic suppression: Stalker, a retrovirus-like transposable element, can compensate for a deficiency at the cut locus of Drosophila melanogaster.

A number of mutations at the cut locus were induced by non-precise excision of a silent P-element insertion which resulted in deletions at the regulatory region of the locus. Unexpectedly, a reversion of one of these mutations was found, which appears as a result of insertion of Stalker (a retrovirus-like mobile element) near the 1.3 kb deletion. Thus an insertion of a retrovirus-like mobile element can suppress the deficiency at the regulatory region of a gene.

Animals↗