Types Of Transposons Research Articles

Repression of tyrosine hydroxylase is responsible for the sex-linked chocolate mutation of the silkworm, Bombyx mori

Pigmentation patterning has long interested biologists, integrating topics in ecology, development, genetics, and physiology. Wild-type neonatal larvae of the silkworm, Bombyx mori, are completely black. By contrast, the epidermis and head of larvae of the homozygous recessive sex-linked chocolate (sch) mutant are reddish brown. When incubated at 30 degrees C, mutants with the sch allele fail to hatch; moreover, homozygous mutants carrying the allele sch lethal (sch(l)) do not hatch even at room temperature (25 degrees C). By positional cloning, we narrowed a region containing sch to 239,622 bp on chromosome 1 using 4,501 backcross (BC1) individuals. Based on expression analyses, the best sch candidate gene was shown to be tyrosine hydroxylase (BmTh). BmTh coding sequences were identical among sch, sch(l), and wild-type. However, in sch the approximately 70-kb sequence was replaced with approximately 4.6 kb of a Tc1-mariner type transposon located approximately 6 kb upstream of BmTh, and in sch(l), a large fragment of an L1Bm retrotransposon was inserted just in front of the transcription start site of BmTh. In both cases, we observed a drastic reduction of BmTh expression. Use of RNAi with BmTh prevented pigmentation and hatching, and feeding of a tyrosine hydroxylase inhibitor also suppressed larval pigmentation in the wild-type strain, pnd(+) and in a pS (black-striped) heterozygote. Feeding L-dopa to sch neonate larvae rescued the mutant phenotype from chocolate to black. Our results indicate the BmTh gene is responsible for the sch mutation, which plays an important role in melanin synthesis producing neonatal larval color.

Centromere sequence and dynamics in Dictyostelium discoideum

Centromeres play a pivotal role in the life of a eukaryote cell, perform an essential and conserved function, but this has not led to a standard centromere structure. It remains currently unclear, how the centromeric function is achieved by widely differing structures. Since centromeres are often large and consist mainly of repetitive sequences they have only been analyzed in great detail in a handful of organisms. The genome of Dictyostelium discoideum, a valuable model organism, was described a few years ago but its centromere organization remained largely unclear. Using available sequence information we reconstructed the putative centromere organization in three of the six chromosomes of D. discoideum. They mainly consist of one type of transposons that is confined to centromeric regions. Centromeres are dynamic due to transposon integration, but an optimal centromere size seems to exist in D. discoideum. One centromere probably has expanded recently, whereas another underwent major rearrangements.In addition to insights into the centromere organization and dynamics of a protist eukaryote, this work also provides a starting point for the analysis of the evolution of centromere structures in social amoebas by comparative genomics.

MGDD: Mycobacterium tuberculosis Genome Divergence Database

BackgroundVariation in genomes among different closely-related organisms can be linked to phenotypic differences. A number of mechanisms, such as replication error, repeat expansion and contraction, recombination and transposition can contribute to genomic differences. These processes lead to generation of SNPs, different types of repeat-based and transposons or IS-element-based polymorphisms, inversions and duplications and changes in synteny. A database of all the variations in a group of organisms is not only useful for understanding genotype-phenotype relationship but also in clinical applications. There is no database available at present that provides information about detailed genomic variations among different strains and species of Mycobacterium tuberculosis complex, organisms responsible for human diseases.DescriptionMGDD is a free web-based database that allows quick user friendly search to find different types of genomic variations among a group of fully sequenced organisms belonging to M. tuberculosis complex. The searches are based on data generated by pair wise comparison using a tool that has already been described. Different types of variations that can be searched are SNPs, indels, tandem repeats and divergent regions. The searches can be designed to find specific variations either in a given gene or any given location of the query genome with respect to any other genome currently available.ConclusionWeb-based database MGDD can help to find all the possible differences that exists between two strains or species of M. tuberculosis complex. The search tool is very user-friendly and can be used by anyone not familiar with computational methods and will be useful to both clinicians and researchers working on tuberculosis and other Mycobacterial diseases.

DNA Transposons and the Evolution of Eukaryotic Genomes

Transposable elements are mobile genetic units that exhibit broad diversity in their structure and transposition mechanisms. Transposable elements occupy a large fraction of many eukaryotic genomes and their movement and accumulation represent a major force shaping the genes and genomes of almost all organisms. This review focuses on DNA-mediated or class 2 transposons and emphasizes how this class of elements is distinguished from other types of mobile elements in terms of their structure, amplification dynamics, and genomic effect. We provide an up-to-date outlook on the diversity and taxonomic distribution of all major types of DNA transposons in eukaryotes, including Helitrons and Mavericks. We discuss some of the evolutionary forces that influence their maintenance and diversification in various genomic environments. Finally, we highlight how the distinctive biological features of DNA transposons have contributed to shape genome architecture and led to the emergence of genetic innovations in different eukaryotic lineages.

Cloning of Novel Repeat-associated Small RNAs Derived from Hairpin Precursors in <italic>Oryza sativa</italic>

Plant small non-coding RNAs including microRNAs (miRNAs), small interfering RNAs (siRNAs) and trans-acting siRNAs, play important roles in modulating gene expression in cells. Here we isolated 21 novel endogenous small RNA molecules, ranging from 18 to 24 nucleotides, in Oryza sativa that can be mapped to 111 hairpin precursors. Further analysis indicated that most of these hairpin sequences originated from putative miniature inverted-repeat transposable elements, a major type of DNA transposon. Considering that miRNA is characteristic of hairpin-like precursor and plant endogenous siRNAs are often located at transposon regions, we hypothesized that our cloned small RNAs might represent the intermediate product in the evolutionary process between siRNAs and miRNAs. Northern blot analysis indicated that five of them were much more abundantly expressed in flower compared to other tissues, implying their potential function in inflorescence. In conclusion, our results enrich rice small RNA data and provide a meaningful perspective for small RNA annotation in plants.

Characterisation of Aft1 a Fot1/Pogo type transposon of Aspergillus fumigatus

In recent years the filamentous fungus Aspergillus fumigatus has become a significant cause of infection in man and as such has become the focus of much study. It is thought to be the leading mould pathogen in leukaemia and transplant patients and is responsible for mortality in a large number of individuals with immunological disorders. In an attempt to develop molecular mutagenesis tools for assessment of this organism, the genome of A. fumigatus was analysed to identify possible functional transposable elements. An apparently intact Fot1/Pogo type transposon with 65% identity to the active Tan1 element of Aspergillus niger was identified and designated Aft1. Aft1 is a 1.9 kb element present in multiple (>20) highly conserved copies. It encodes a 332 amino acid transposase which contains all the functional motifs required for transposition. In addition, the transposase was expressed in cultures grown at 37 °C in all three strains assessed and excision analysis suggests Aft1 may be active and of use in transposon tagging experiments. Southern hybridisation patterns indicate that Aft1 is widely distributed amongst clinical isolates of A. fumigatus with considerable variation in genomic localisation. A comprehensive analysis of the genomic localisation of Aft1 in the sequenced strain AF293 show that one insertion is 30 bases upstream of a predicted gene encoding a G-protein coupled receptor. Expression analysis indicates that this gene has been inactivated by the insertion.

Transposon Tn 7 Is Widespread in Diverse Bacteria and Forms Genomic Islands

We find that relatives of the bacterial transposon Tn7 are widespread in disparate environments and phylogenetically diverse species. These elements form functionally diverse genomic islands at the specific site of Tn7 insertion adjacent to glmS. This work presents the first example of genomic island formation by a DDE type transposon.

Mechanisms and Rates of Birth and Death of Dispersed Duplicated Genes during the Evolution of a Multigene Family in Diploid and Tetraploid Wheats

A family of 5 genes that evolved within the past 1.9 Myr in diploid wheat was characterized. The ancestral gene, ALP-A1, is on chromosome 1A and encodes an aci-reductone dioxygenase-like protein. The duplicated genes ALP-A2, ALP-A3, ALP-A4.1, and ALP-A4.2 acquired complete coding sequences but lost the original promoter. They are on chromosomes 4A, 2A, 6A and 6A, respectively, and evolved sequentially, the youngest duplicated gene always producing the next duplicate. It is shown that dispersed gene duplication rate consists of the primary rate (duplications of ancestral genes) and the secondary rate (duplications of genes that had been generated by recent duplications). The primary rate was 2.5 x 10(-3) gene(-1) Myr(-1) in diploid wheat. The secondary rate was 5.2 x 10(-2) gene(-1) Myr(-1) in the ALP family. The 20-fold acceleration of the secondary rate was caused by the insertion of the ALP-A2 gene into a novel type transposon. Only the ALP-A1 and ALP-A3 genes are transcribed. The transcription of ALP-A3 is directed by a promoter within a DNA fragment similar to a CACTA type of DNA transposons, making ALP-A3 a new gene. The ALP-A3 transcript is longer than that of the ALP-A1. The half-life of ALP duplicated genes was estimated to be 0.87 Myr. Strong purifying selection acting on the ancestral gene ALP-A1 was undiminished by the evolution of duplicated genes. The evolution of the ALP family shows that repeated elements facilitate both gene duplication and expression of duplicated genes and highlights their importance for the evolution of gene repertoire in large plant genomes.

Role of Horizontal Transfer of the Transposon Tn1546in the Nosocomial Spread ofvanAVancomycin-Resistant Enterococci at a Tertiary Care Hospital in Korea

To investigate the epidemiologic characteristics of vancomycin-resistant enterococci (VRE) infection. An epidemiologic description by means of chromosomal DNA fingerprinting and transposon typing. A 2,200-bed tertiary care hospital in Korea. First VRE isolates were obtained from patients hospitalized from April 1997 to December 2001. The van genotypes of isolates were identified by means of multiplex polymerase chain reaction (PCR). The macrorestriction patterns of chromosomal DNA were determined by pulsed-field gel electrophoresis (PFGE). The transposon Tn1546 was typed by means of 2 sets of long PCR restriction fragment-length polymorphism analysis, which were ClaI restriction of a 10.4-kb region from orf1 to vanZ and DdeI restriction of a 4.4-kb region from vanR to vanX. VRE isolates were recovered from 215 patients. All were vanA genotype. PFGE analysis of the 215 isolates showed 172 types, including 21 clusters composed of 64 isolates and 151 types of as many isolates. Each type was composed of 2-10 isolates; the isolates within each PFGE cluster were detected within a 10-month period and mostly shared a transposon type. Transposon typing classified 169 strains into 15 types and 158 strains belonged to 4 major transposon clusters. Each of these 4 transposon clusters was isolated from patients treated in 5-22 different wards during a 31-52 month period and consisted of 9-80 PFGE types. Each of the other 11 types were found in only one strain. Our findings suggest that the horizontal transfer of Tn1546 has a major role in the nosocomial spread of vanA VRE. Clonal spread of VRE seemed to contribute to short-term dissemination in limited areas.

High-Throughput Transposon Mutagenesis of Corynebacterium glutamicum and Construction of a Single-Gene Disruptant Mutant Library

A simple and high-throughput transposon-mediated mutagenesis system employing two different types of transposons in combination with direct genomic DNA amplification and thermal asymmetric interlaced PCR (TAIL-PCR) was developed. Each of the two minitransposons based on IS31831 (ISL3 family) and Tn5 (IS4 family) was integrated into the Corynebacterium glutamicum R genome. By using BLAST and Perl, transposon insertion locations were automatically identified based on the sequences of TAIL-PCR products of mutant cells. Insertion locations of 18,000 mutants were analyzed, and a comprehensive insertion library covering nearly 80% of the 2,990 open reading frames of C. glutamicum R was generated. Eight thousand of the mutants, exhibiting disruption in 2,330 genes, survived on complex medium under normal laboratory conditions, indicating that the genes were not essential for cell survival. Of the 2,330 genes, 30 exhibited high similarity to essential genes of Escherichia coli or Bacillus subtilis. This approach could be useful in furthering genetic understanding of cellular life and facilitating the functional analysis of microorganisms.

Anaconda, a new class of transposon belonging to the Mu superfamily, has diversified by acquiring host genes during rice evolution

A new type of transposon, named Anaconda (Anac) has been found in rice (Oryza sativa). In this paper, we demonstrate that Anaconda elements have diversified by acquisition of host cellular genes, amplification of the elements, and substitution and deletion of short segments. We identified four Anaconda elements in studies of rice alternative oxidase (AOX) genes, and subsequently isolated an additional 23 elements based on the identity of their terminal inverted repeats (TIRs). The Anaconda elements have long TIRs (114-458 bp). They also have direct repeats of 9 or 10 bp in their flanking regions that are thought to have been generated upon transposition. These structural features reveal that the Anaconda elements belong to the Mu superfamily. The most prominent feature of the Anaconda elements is the high frequency with which they have acquired host cellular genes. Of the 27 elements found here, 19 appear to have sequences presumably derived from rice genes, for example, the genes for AOX1c (four elements), cytochrome P450 (five elements), L: -asparaginase (five elements), and PCF8 (two elements). Four elements, AnacA1-A4, have both the AOX1c and P450 genes. One element, AnacB14, involves a gene similar to mudrA of maize MuDR. Database analyses revealed that the loci of 26 of the 27 Anaconda elements in the subspecies japonica are the same as those in the subspecies indica. This suggests that these elements were incorporated before the divergence of these two subspecies.

Mutator-like element in the yeast Yarrowia lipolytica displays multiple alternative splicings.

A new type of DNA transposon, Mutyl, has been identified in the sequenced genome of the yeast Yarrowia lipolytica. This transposon is 7,413 bp long and carries two open reading frames (ORFs) which potentially encode proteins of 459 and 1,178 amino acids, respectively. Whereas the first ORF shows no significant homology to previously described proteins, the second ORF shows sequence similarities with various Mutator-like element (MULE)-encoded transposases, including the bacterial transposase signature sequence. Other MULE features shared by Mutyl include a zinc finger motif in the putative transposase, a 22-bp-long imperfect inverted repeat at each end, and a 9- to 10-bp duplication of its target site in the chromosome. Of the five copies of Mutyl present in the genome, one has a deletion of the first 8 bases, and the others are full length with a single base change in one element. The first potential gene of Mutyl, mutB, was shown to be expressed in exponentially growing cells. Its sequence contains a predicted intron with two 5' splice sites, a single branch point, and two 3' splice sites. Its mRNA is alternatively spliced, as judged by reverse transcription-PCR, and generates four mRNAs corresponding to protein-coding sequences of 128, 156, 161, and 190 amino acids. Of the three distinct lineages characterized in Y. lipolytica, strains from the German lineage and the French lineage do not carry Mutyl. A study of the distribution of Mutyl in strains of the French lineage evidenced a recent transposition event. Taken together, these results indicate that Mutyl is still active.

Alternative splicing of transcripts of the transposon Restless is maintained in the foreign host Neurospora crassa and can be modified by introducing mutations at the 5' and 3' splice sites.

The primary transcript of the transposon Restless from Tolypocladium inflatum undergoes an unusual mechanism of alternative splicing by employing either of two 3' "CAG" splice sites. These are separated by only four nucleotides, thus generating two different splice products, which differ in their coding capacity. To analyse whether this alternative splicing occurs in its natural host exclusively, we introduced the transposon into the heterologous host Neurospora crassa. In addition to the wild -type transposon sequence, transposon sequences mutagenised in vitro with modified 5' and 3' intron splice sites were generated. RNA was isolated from transformants and RT-PCR was performed with specific oligonucleotides flanking the intron sequence. Alternative splicing was analysed, employing a simple test procedure based on the convenient presence of a BamHI restriction site between both splice sites. The ratio of alternative splicing seems to be influenced by both the 5' and the 3' splice site, as mutations at either position influence the ratio of alternative splice products. At the 5' splice site, mutating the first "C" has a strong effect on the ratio of alternative splicing, while mutating the second "C" has little or no effect. Similarly, at the 3' splice site, only mutations at the first 3' "CAG" change the ratio of alternative splicing. It appears that alternative splicing of the Restless intron is not host-specific, but is influenced by the intron splice site sequences themselves.

Activity of the En/Spm-like transposons in meiosis as a base for chromosome repatterning in a small, isolated, peripheral population of Aegilops speltoides Tausch.

Chromosomal repatterning is considered to be one of the main mechanisms for plant genome evolution. Here, we report the first cytogenetic evidence for the involvement of En/Spm transposons in ongoing chromosomal repatterning leading to the rise of new fertile genomic forms in a small, isolated, peripheral plant population. Cytogenetical screening of original individual plants of Aegilops speltoides Tausch. with different phenotypes revealed a wide spectrum of chromosomal abnormalities including extra chromosomes, chromosomal rearrangements, and variability in chromosomal position/number of 45S and 5S rDNA sites. Cytogenetic analysis of the dynamics of En/Spm transposons in meiosis indicates that: (i) this type of transposon is active during male gametogenesis; (ii) separately or in conjunction with rDNA they form clusters in the hot spots of large chromosomal rearrangements; (iii) appearance of at least part of the mobile rDNA sites in genome of Ae. speltoides are connected with meiotic activity of En/Spm transposons. PCR screening for the site-selected transposon insertions confirm the presence of combined fragments that consist partly of the sequence of En/Spm transposon and partly of 5S rDNA sequence.

End-joining of blunt DNA double-strand breaks in mammalian fibroblasts is precise and requires DNA-PK and XRCC4

DNA double-strand break repair by non-homologous end-joining (NHEJ) is generally considered to be an imprecise repair pathway. In order to study repair of a blunt, 5′ phosphorylated break in the DNA of mammalian fibroblasts, we used the E. coli cut-and-paste type transposon Tn5. We found that the Tn5 transposase can mediate transposon excision in Chinese hamster cell lines. Interestingly, a blunt 5′ phosphorylated break could efficiently be repaired without loss of nucleotides in wild type fibroblasts. Catalytic subunit of DNA-dependent protein kinase (DNA-PK CS) deficiency reduced the efficiency of joining four-fold without reducing precision, whereas both efficiency and accuracy of joining were affected in Ku80 or XRCC4 mutant cell lines. These results show that both the DNA-PK and the XRCC4/ligase IV complexes are required for NHEJ and that other, more error-prone, repair processes cannot efficiently substitute for joining of blunt breaks produced in living cells. Interestingly, the severity of the end-joining defect differs between the various mutants, which may explain the difference in the severity of the phenotypes, which have been observed in the corresponding mouse models.

Structural and transcriptional analysis of S -locus F-box genes in Antirrhinum

A class of ribonucleases termed S-RNases, which control the pistil expression of self-incompatibility, represents the only known functional products encoded by the S locus in species from the Solanaceae, Scrophulariaceae and Rosaceae. Previously, we identified a pollen-specific F-box gene, AhSLF (S locus F-box)-S 2, very similar to S 2 -RNase in Antirrhinum, a member of the Scrophulariaceae. In addition, AhSLF-S 2 also detected the presence of its homologous DNA fragments. To identify these fragments, we constructed two genomic DNA libraries from Antirrhinum self-incompatible lines carrying alleles S 1 S 5 and S 2 S 4, respectively, using a transformation-competent artificial chromosome (TAC) vector. With AhSLF-S 2-specific primers, TAC clones containing both AhSLF-S 2 and its homologs were subsequently identified (S 2 TAC, S 5 TACa, S 4 TAC, and S 1 TACa). DNA blot hybridization, sequencing and segregation analyses revealed that they are organized as single allelic copies (AhSLF-S 2, -S 1, -S 4 and -S 5) tightly linked to the S-RNases. Furthermore, clusters of F-box genes similar to AhSLF-S 2 were identified. In total, three F-box genes (AhSLF-S 2, -S 2 A and -S 2 C) in S 2 TAC (51 kb), three (AhSLF-S 4, -S 4 A and -S 4 D) in S 4 TAC (75 kb), two (AhSLF-S 5 and -S 5 A) in S 5 TACa (55 kb), and two (AhSLF-S 1 and -S 1 E) in S 1 TACa (71 kb), respectively, were identified. Paralogous copies of these genes show 38–54% identity, with allelic copies sharing 90% amino acid identity. Among these genes, three (AhSLF-S 2 C, -S 4 D and -S 1 E) were specifically expressed in pollen, similar to AhSLF-S 2, implying that they likely play important roles in pollen, whereas three AhSLF-SA alleles showed no detectable expression. In addition, several types of retroelements and transposons were identified in the sequenced regions, revealing some detailed information on the structural diversity of the S locus region. Taken together, these results indicate that both single allelic and tandemly duplicated genes are associated with the S locus in Antirrhinum. The implications of these findings in evolution and possible roles of allelic AhSLF-S genes in the self-incompatible reaction are discussed in species like Antirrhinum.

Diversity of tn1546-like elements in vancomycin-resistant enterococci isolated from humans and poultry in Korea.

To investigate the possible spread of vancomycin resistance among enterococci through horizontal gene transfer between two sources of vancomycin-resistant enterococci (VRE) isolated from farm animals and humans in Korea, molecular characterization of VRE isolated from poultry (20 isolates) and humans (35 isolates) was performed by PCR-restriction fragment length polymorphism typing of the vanA gene cluster (Tn1546). PCR mapping of Tn1546 finally distinguished seven different transposon types (types A to G). Type A was observed only in the poultry isolates, while the other six types were present only in the human isolates. An insertion sequence and deleted sequence were detected in most of the human isolates in the orf2-vanR and vanX-vanY regions in the Tn1546-like element, but not in the poultry isolates. Tn1546-like elements were found in conjugal plasmids of most human VRE, whereas they were detected in the chromosomes of all poultry VRE. Accordingly, no evidence was found of any recent transmission of vancomycin resistance genes between poultry and humans in Korea.

Antibiotic resistance of faecal enterococci in poultry, poultry farmers and poultry slaughterers.

The prevalence of resistance in enterococci to antibiotics, commonly used for therapy in poultry or as antimicrobial growth promoters (AMGPs), was determined in faecal samples of two chicken populations: broilers in which antibiotic and AMGP use is common and laying-hens with a low antibiotic usage. In addition faecal samples were examined from three human populations: broiler farmers, laying-hen farmers and poultry slaughterers. MICs of an extended panel of antibiotics for a randomly chosen gentamicin- or vancomycin-resistant enterococcal isolate from each faecal specimen were also determined. The prevalence of resistance for all antibiotics tested was higher in broilers than in laying-hens. Resistance in faecal enterococci of broiler farmers was for nearly all antibiotics higher than those observed in laying-hen farmers and poultry slaughterers. The overall resistance in broilers was correlated with the resistance in broiler farmers and in poultry slaughterers. No correlation between the results obtained in the laying-hens with any of the other populations was found. The 27 gentamicin-resistant isolates all showed high-level resistance to gentamicin and two of these isolates, both Enterococcus faecium, were resistant to all antibiotics tested, except vancomycin. The 73 vancomycin-resistant enterococci (VRE) isolated from the five populations belonged to four different species and in all isolates the vanA gene cluster was detected by blot hybridization. The pulsed-field gel electrophoresis (PFGE) patterns of these vancomycin-resistant enterococci were quite heterogeneous, but Enterococcus hirae isolates with the same or a closely related PFGE pattern were isolated at two farms from the broiler farmer and from broilers. Molecular characterization of vanA-containing transposons of these isolates showed that similar transposon types, predominantly found in poultry, were present. Moreover, similar vanA elements were not only found in isolates with the same PFGE pattern but also in other VRE isolated from both humans and chickens. The results of this study suggest transmission of resistance in enterococci from animals to man. For VRE this might be clonal transmission of animal strains, but transposon transfer seems to occur more commonly.

Phylogenetic analysis reveals stowaway-like elements may represent a fourth family of the IS630-Tc1-mariner superfamily.

The genomes of plants, like virtually all other eukaryotic organisms, harbor a diverse array of mobile elements, or transposons. In terms of numbers, the predominant type of transposons in many plants is the miniature inverted-repeat transposable element (MITE). There are three archetypal MITEs, known as Tourist, Stowaway, and Emigrant, each of which can be defined by a specific terminal inverted-repeat (TIR) sequence signature. Although their presence was known for over a decade, only recently have open reading frames (ORFs) been identified that correspond to putative transposases for each of the archetypes. We have identified two Stowaway elements that encode a putative transposase and are similar to members of the previously characterized IS630-Tc1-mariner superfamily. In this report, we provide a high-resolution phylogenetic analysis of the evolutionary relationship between Stowaway, Emigrant, and members of the IS630-Tc1-mariner superfamily. We show that although Emigrant is closely related to the pogo-like family of elements, Stowaway may represent a novel family. Integration of our results with previously published data leads to the conclusion that the three main types of MITEs have different evolutionary histories despite similarity in structure.

Mobilization of a Drosophila transposon in the Caenorhabditis elegans germ line.

Transposons have been enormously useful for genetic analysis in both Drosophila and bacteria. Mutagenic insertions constitute molecular tags that are used to rapidly clone the mutated gene. Such techniques would be especially advantageous in the nematode Caenorhabditis elegans, as the entire sequence of the genome has been determined. Several different types of endogenous transposons are present in C. elegans, and these can be mobilized in mutator strains (reviewed in ref. 1). Unfortunately, use of these native transposons for regulated transposition in C. elegans is limited. First, all strains contain multiple copies of these transposons and thus new insertions do not provide unique tags. Second, mutator strains tend to activate the transposition of several classes of transposons, so that the type of transposon associated with a particular mutation is not known. Here we demonstrate that the Drosophila mariner element Mos1 can be mobilized in C. elegans. First, efficient mobilization of Mos1 is possible in somatic cells. Second, heritable insertions of the transposon can be generated in the germ line. Third, genes that have been mutated by insertion can be rapidly identified using inverse polymerase chain reaction. Fourth, these insertions can subsequently be remobilized to generate deletion and frameshift mutations by imperfect excision.