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 mobility of transposable elements via a cut-and-paste mechanism depends on the elaboration of a nucleoprotein complex known as the synaptic complex. We show here that the Mos1 synaptic complex consists of the two inverted terminal repeats of the element brought together by a transposase tetramer and is designated paired-end complex 2 (PEC2). The assembly of PEC2 requires the formation of a simpler complex, containing one terminal repeat and two transposase molecules and designated single-end complex 2 (SEC2). In light of the formation of SEC2 and PEC2, we demonstrate the presence of two binding sites for the transposase within a single terminal repeat. We have found that the sequence of the Mos1 inverted terminal repeats contains overlapping palindromic and mirror motifs, which could account for the binding of two transposase molecules "side by side" on the same inverted terminal repeat. We provide data indicating that the Mos1 transposase dimer is formed within a single terminal repeat through a cooperative pathway. Finally, the concept of a tetrameric synaptic complex may simply account for the inability of a single mariner transposase molecule to interact at the same time with two kinds of DNA: the inverted repeat and the target DNA.Mos1 is an autonomous mariner transposable element first isolated from Drosophila mauritiana. It is 1,286 bp long, with 28-bp imperfect inverted terminal repeats (ITR), and contains a single open reading frame encoding a 345-amino-acid transposase (Tnp). On the basis of the sequence of the Tnp and the organization of the element, mariner has been grouped together with the Tc1 and pogo transposable elements to form the Tc1/mariner superfamily (27). One of the main properties of the Tc1/mariner elements is that they do not require host factors for their mobility, because the Tnp is sufficient to promote all the transposition steps. This property accounts for the wide distribution of the Tc1/mariner superfamily among eukaryotic organisms and makes it possible to develop DNA transfer vectors based on Tc1/mariner elements (22).mariner transposes by a cut-and-paste mechanism, similar to that described for related bacterial insertion sequences (4). Briefly, the two ends of the elements are brought together by transposase oligomerization to form a synaptic complex that triggers cleavages at the transposon ends. This complex is usually designated a paired-end complex (PEC). The Tnp then promotes the integration of the excised transposon at a new target site. Assembling the highly organized synaptic complex is the key of transposition, in which the cleavages progress step by step. The structure of this synaptic complex has been elucidated for several prokaryotic transposons, such as Tn5. In this case, the molecular assembly is dimeric: each doublestranded DNA molecule is bound to both Tnp subunits (8). In other cases, where no crystallographic data are available, the exact stoichiometry of the complex has yet to be defined, as explained for IS911 (21). No complete synaptic complex has s...

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

To examine directly the interaction of circulating proteins (CP) with the glycocalyx of pulmonary endothelium and its effect on endothelial permeability, two types of experiments were carried out. In the first, rats were exchange transfused with graded amounts of FC-43 fluorocarbon emulsion (FCE) resulting in CP concentrations of 25, 10, and 4 mg/ml, respectively. In the second, rats were exchange transfused with FCE to remove 99.9% of CP. The rats were then exchange transfused with 1 ml FCE containing 60 mg/ml of rat serum protein and killed 3.5, 7.5, and 15 min after the administration of protein. In all animals the distribution of albumin and immunoglobulin G (IgG) was visualized by immunocytochemistry, and endothelial permeability to native ferritin was measured by morphometry. In the depletion experiments increased endothelial permeability to ferritin coincided with loss of adsorbed albumin and IgG from the glycocalyx. Conversely, the presence of administered serum proteins in the glycocalyx and in a few luminal vesicles was associated with an endothelial permeability to ferritin indistinguishable from that of controls. These observations suggest that the adsorption of CP to the endothelial glycocalyx renders the underlying endothelium less permeable to ferritin.

No abstract