The wild-type conformation of the Mos-1 inverted terminal repeats is suboptimal for transposition in bacteria.

The two inverted terminal repeats (ITRs) flanking the Mos-1 mariner element differ in sequence at four positions. Gel retardation experiments indicated that each of these differences has a significant impact on the quality of the interaction between the ITR and the Mos-1 transposase. We showed that the transposase binds to the 3' ITR better than to the 5' ITR. The results of transposition assays performed in Escherichia coli indicated that these differences have an influence on the rate of transposition and the stability of the transposition products. Finally, we find that the wild-type configuration of the Mos-1 element, with one 5' ITR and one 3' ITR, is less efficient for transposition in bacteria than that of an element having two 3' ITRs.

The ITR binding domain of the Mariner Mos-1 transposase.

Mariner-like elements are widespread eukaryotic transposons, but Mos-1 is the only natural element that is known to be active. Little is known about the biochemistry of mariner transposition. The first step in the process is the binding of the transposase to the 5' and 3' inverted terminal repeats (ITRs) of the element. Using the 3' ITR of the element, we have determined the binding properties of a recombinant Mos-1 transposase produced in bacteria, and we have used deletion derivatives to localize the minimal ITR binding domain between amino acids 1 and 141. Its features and structure indicate that it differs from the ITR binding domain of the transposase encoded by Tc1-related elements.

Features of the mammal mar1 transposons in the human, sheep, cow, and mouse genomes and implications for their evolution.

Mariner-like elements (MLE) belong to the Tc1/ mariner superfamily of class II transposons. We have analyzed the mariner related to the cecropia subfamily, and called mammal mar1, in four mammalian genomes, Bos taurus (Bovidae), Homo sapiens (Primata), Mus musculus (Rodentia), and Ovis aries (Ovidae). Three kinds of MLE sequences were found in all these species: full-length 1.3-kbp elements, shorter elements 80 bp-1.2 kbp, and single inverted terminal repeats (ITRs). All the 1.3-kbp genomic copies sequenced had an open reading frame encoding a transposase interrupted by stop codons or frame shifts. Phylogenetic analysis of the full-length elements suggested at least two distinct populations of mammal mar1 elements in each species. This was confirmed by using a statistical method that allows defining populations. Finally, the evolutionary origin of the mammal mar1 elements and the paradoxes are discussed.

Particle and genomic characteristics of a new member of the Ascoviridae: Diadromus pulchellus ascovirus.

A new member of the family Ascoviridae, Diadromus pulchellus ascovirus (DpAV), has been found in the lepidopteran nymphs of Acrolepiopsis assectella parasitized by the hymenopteran wasp Diadromus pulchellus. Virions have the standard features of the ascovirus group; each particle is about 220 nm long and 150 nm wide. They are multilayered, with two clear 7-nm-thick outer layers and one 15-nm-thick inner layer surrounding an electron-dense core (155 x 110 nm). However, the flattened rice-grain shape and fragility of the DpAV particles are unlike that of known ascoviruses infecting Noctuidae species. They form large vesicles containing virions in infected cells. The DpAV genome is about 116 kb long and has a circular and relaxed structure. It contains 6-8 repeated and interspersed sequences of 494 bp. The structural and genomic features of DpAV suggest that this virus belongs to an ascovirus sub-family different from that containing the ascoviruses previously found to infect species of Noctuidae (Federici et al., 1991).

Biological and molecular features of the relationships between Diadromus pulchellus ascovirus, a parasitoid hymenopteran wasp (Diadromus pulchellus) and its lepidopteran host, Acrolepiopsis assectella.

The Diadromus pulchellus ascovirus (DpAV) has been isolated from laboratory strains of Diadromus pulchellus and in natural wild populations collected from the Antibes locality (southern France). The DpAV genome was found in the cells of the head, thorax and abdomen of this hymenopteran wasp. DpAV virions are present in the female genitalia and are transmitted to the nymphal lepidopteran host, Acrolepiopsis assectella, at each oviposition of the female wasp. The presence of the DpAV genome in all Diadromus somatic cells suggests that it is inherited by vertical transmission. DpAV is amplified in the host tissues during the larval development of D. pulchellus in A. assectella. Cell lysis due to amplification of the virus does not prevent the development of the hymenopteran larva. Virus amplification appears to be slower in nymphs parasitized by D. pulchellus than in nymphs artificially infected with DpAV alone. Lysis of the nymphal cells due to viral replication seems to be synchronous with egg hatching and the development of the hymenopteran larva. The features of DpAV and its relationship with the parasitoid wasp D. pulchellus during its development are compared to those of the ichnoviruses.

Human and other mammalian genomes contain transposons of the mariner family.

Internal fragments of the putative transposase gene of mariner-like elements (MLEs) were amplified from human, mouse, rat, chinese hamster, sheep and bovine genomic DNAs by polymerase chain reaction (PCR). The sequences identified in human, ovine and bovine genomes correspond to ancient degenerate transposons. Screening mammalian sequence libraries identified a truncated element in the human ABL gene and the sequence of its 5'-ITR was determined. This ITR sequences were used in PCR experiments with DNA from six mammalian species and detected full-sized and deleted MLEs. The presence of MLE in mammalian genomes demonstrates that they are ubiquitous mobile elements found from fungi to man. This observation strongly raises the possibility that MLE could constitute tools for the modification of eucaryotic genomes.

The genome segments of DpRV, a commensal reovirus of the wasp Diadromus pulchellus (Hymenoptera).

The complete nucleotide sequences of the five double-stranded RNA genome segments of the Diadromus pulchellus reovirus (DpRV) have been determined. They consist of 985, 1240, 1318, 1652, and 4230 bp. Each segment contains at least one putative open reading frame encoding 33-, 40-, 45-, 49-, and 148-kDa proteins, respectively. The proteins have no significant similarities with sequences in data banks. Analysis of these segments and of two other previously published segments revealed the presence of degenerate consensus inverted repeats at both ends (5'-rCAAUUUUnnACU...AGUAAAAAAAUnrG-3'). The biological, structural, and genomic features of DpRV suggest that this virus is related to members of the Orthoreovirus genus.

A member of the reoviridae (DpRV) has a ploidy-specific genomic segment in the wasp Diadromus pulchellus (Hymenoptera).

Wild and laboratory populations of the parasitoid wasp Diadromus pulchellus are infected with a new member of the reoviridae (DpRV) described in this paper. The particles of this virus possess two capsid shells (diameters: 35 and 70 nm) made up of 11 proteins. The virus is present mainly in the gut of the wasp, with smaller quantities in its venom gland. The genome of virus particles purified from haploid insects (functional males) contains 10 segments, whereas virus from diploid insects (females and sterile diploid males) contains a supernumerary 3.33-kb segment. The sequence of this dsRNA segment revealed that it is a triplicated 1050-bp motif which is 97.5% similar to the 5' region of one of the 10 basic segments, the 3.80-kb segment.

Mariner-like elements in hymenopteran species: insertion site and distribution.

Copies of mariner-like element (MLE) transposons in two species, the bumble bee, Bombus terrestris, and the ant, Myrmica ruginodis, were sequenced. The full-sized elements are 1250 bp long in both species and include 28-bp inverted terminal repeats. The five copies sequenced were approximately 75% similar to a mariner element (peach) of Drosophila mauritiana. The distribution of MLE in 27 hymenopteran species was studied by PCR and Southern blot hybridization; 93% of the species contained one or more of the four major forms of the element. They are inserted in their host genomes, in the middle of a degenerated 30-bp palindrome, which is itself located in an 85-bp conserved region with a purine-rich tail at one of its ends. The hymenopteran MLEs lie in a specific insertion site, suggesting that this region is conserved. It is thus possible that this region may be a selectively neutral insertion site, which would explain why these elements are widespread in hymenopteran genomes and are not eliminated by male haploidy.

The evolutionary genetics of the hobo transposable element in the Drosophila melanogaster complex.

Hobo elements are a family of transposable elements found in Drosophila melanogaster and its three sibling species: D. simulans, D. mauritiana and D. sechellia. Studies in D. melanogaster have shown that hobo may be mobilized, and that the genetic effects of such mobilizations included the general features of hybrid dysgenesis: mutations, chromosomal rearrangements and gonadal dysgenis in F1 individuals. At the evolutionary level some hobo-hybridizing sequences have also been found in the other members of the melanogaster subgroup and in many members of the related montium subgroup. Surveys of older collected strains of D. melanogaster suggest that complete hobo elements were absent prior to 50 years ago and that they have recently been introduced into this species by horizontal transfer. In this paper we review our findings and those of others, in order to precisely describe the geographical distribution and the evolutionary history of hobo in the D. melanogaster complex. Studies of the DNA sequences reveal a different level of divergence between the group D. melanogaster, D. simulans and D. mauritiana and the fourth species D. sechellia. The hypothesis of multiple transfers in the recent past into the D. melanogaster complex from a common outside source is discussed.

The occurrence of the transposable element pogo in Drosophila melanogaster.

We examined the genomic occurrence of the transposable element pogo in over 120 strains of Drosophila melanogaster, from around the world and from different eras. All had multiple copies of a 2.1 kilobase (kb) pogo element, and multiple copies of several size classes between 1.0 and 1.8 kb. There were differences between strains in intensities or presences of deletion-derivative size classes, suggesting current or recent mobility in the species. We were unable to find any pogo-hybridization in eight other species in the genus, in three subgenera, or in the related Scaptomyza pallida. The pogo element may be a 'middle-aged' element in the genome of D. melanogaster, having entered the species since its divergence from its sibling species, but long before the P and hobo elements.

The 28S ribosomal RNA-encoding gene of Hymenoptera: inserted sequences in the retrotransposon-rich regions.

The genomes of two parasitoid wasps, Diadromus pulchellus and Eupelmus vuilleti, and the honey bee, Apis mellifera, contain few interspersed repeated sequences corresponding to transposons (Tn). This suggests that the genomic organisation of Hymenoptera could be due to the elimination of deleterious Tn in haploid males. We have used restriction-fragment length polymorphism analysis to show that nondeleterious Tn are present in the DNA (rDNA) encoding ribosomal RNA of twelve species of Hymenoptera. Sequence analysis of the 28S rDNA type-I and type-II insertion-rich regions of 80 species showed that this region is very highly conserved (95.8%). A consensus sequence and restriction map of the rDNA region were established. These sequence data were used to develop a strategy for detecting inserted elements in the rDNA fragments containing type-I or type-II insertion sites, and this strategy was used to screen twelve hymenopteran species and four non-Hymenoptera control species. The rDNA fragments from the Hymenoptera and control species contained inserted sequences in the area where type-I and type-II elements are inserted in the 28S rDNA retrotransposon-rich region of Diptera and Lepidoptera. The hymenopteran genomes therefore appear to contain repeated elements, the mobility and nature of which remain to be determined.

Heterochromatin condensation and evolution of unique satellite-DNA families in two parasitic wasp species: Diadromus pulchellus and Eupelmus vuilleti (Hymenoptera).

Large quantities of satellite DNA families (15%-25% of the genome) were found in the DNA of two species of parasitic wasps, Diadromus pulchellus and Eupelmus vuilleti. In both species the satellite DNA was found to consist wholly or largely of a single family unique to that species. Several clones of each family were obtained and sequenced. Palindromes in each consensus sequence suggest the formation in vivo of hairpin structures that may play a role in the mode of heterochromatin condensation in these insects. The ancestral repeating motifs were determined from the consensus sequences. Plausible scenarios are presented for the evolution of the two satellite DNAs. The occurrence of only one family of satellite DNAs in both species may indicate that, in male haploids, such families have shorter persistence times than necessary for the origins of new duplicated sequences.

Are Drosophila melanogaster populations under a stable geographical differentiation due to the presence of P elements?

In order to simulate the outcome of the P-M status of Eurasian populations of Drosophila melanogaster, the evolution of experimental mixed-strains was monitored for up to 50 generations. The results were compared with the evolution in natura of European populations sampled in 1981-83 and 1986-87 over a similar period of time. Different combinations of P and M' strains, Q and M' strains, M' and M' strains and M and M' strains were set up at 25 degrees C and duplicated at 13 degrees C night-21 degrees C day. The possibility of a change towards a P type only appeared with the introduction of the strong P strain Harwich into Eurasian strains. Strains with strength similar to that of Harwich are not currently found in wild populations. With the introduction of weak P and Q strains of the strength presently observed in western Europe, experimental populations evolved slowly towards a Q state or a weak M' state. M'-M' mixed populations resulted in strong M' strains, as was the case for M-M' populations. In these cases. P sequences were not eliminated. In wild populations both genetic and molecular analyses showed no significant differences, over a five year period, for GD sterility potentials, for total P copy number or for distribution of the full-sized and KP elements. Changes in Eurasian populations are probably taking place at a very low rate and may even have stopped, leading to a quasi-stable differentiation over the continent. During the different steps of progressive invasion of P transposable elements, several deleted elements developed and natural selection may have acted on them. The possibility of the selection of different types of regulatory mechanisms according to the presence of different kinds of derivative elements, leading to a world-wide differentiation between P-Q and M' strains is discussed.