P-element excision

Romeijn RJ, Gorski MM, van Schie MA, Noordermeer JN, Mul-lenders LH, Ferro W, Pastink A. Lig4 and rad54 are required for repair of DNA double-strand breaks induced by P-element excision in Drosophila. Genetics 2005 169 795-806. 

Figure 1. Diagrammatic representation of the P-element excision assay in embryonic soma.

The failure to observe P-element excision in A. suspensa and P. interpunctella embryos suggests that P-elements may not be functional in all insects. Although the reason for the lack of functionality has not been identified, the excision assay is designed with adequate latitude for modification so that it is amenable to experimental analysis. With sufficient effort, the biochemical basis for the lack of P-element activity can be identified and potentially be corrected. Preliminary results indicate that the transposase gene carried by the helper plasmid is being transcribed in A. suspensa, and efforts are now underway to determine if all of the posttranscriptional modifications necessary to generate a functional transposase raRNA occur (15). 

The excision assay was tested also in two other Drosophila species to determine the functionality of the assay in other insects. Excision occurred in both D. simulans and D. grirashawii at nearly the same rate as observed in D. melanogaster (Table 1). The transposition activity of the P-element in the embryos of these species demonstrates that the excision assay can be employed as a reliable indicator of P-element behavior in other insects. 

O Hare K, Baibin GM (1983) Structures of P transposable elements and their sites of insertion and excision in the Drosophila melanogaster genome. Cell 34 25-35... 

S. aureus transposons are small mobile elements that often encode resistance genes (P-lactamase, resistance to erythromycin and tetracycline). All the transposons encode a transposase gene, and the product of this gene catalyses excision and/or replication of the element, as well as integration. Horizontal transfer of transposons to other S. aureus cells is presumably mediated by another MGE that is transferred, most likely a plasmid transferred by transduction or conjugation. Conjugative transposons have also been described in S. aureus. However, it is not clear if native conjugative transposons are found in S. aureus (Novick 1990). 

Following this spate of disconnections, one of the rings from the central tricyclic core of resiniferatoxin (1) and two of its perplexing stereocenters have been successfully excised. Several challenging elements still remained for consideration. As shown in Scheme 4, though, if the exocyclic C—C double bond of the a,P-unsaturated system in 10 were modified to an endocyclic variant (15), then the majority of the remaining complexity could be dealt with in one fell swoop as this new adduct could conceivably result from an intramolecular 1,3-dipolar cycloaddition of an alkene and a tethered 3-oxidopyrylium motif (16). This compound, in turn, could be obtained from pyranone 17. 

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