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Penelope is one of the mobile elements mobilized in the progeny of certain Drosophila virilis strains crossed in a certain direction. The progeny displays gonad sterility, numerous mutations, and disturbed chromosome behavior. This syndrome is known as hybrid dysgenesis and is accompanied by the mobilization of several unrelated transposons, with Penelope probably playing the major part. Penelope has a unique structure, combining features of both LTR and poly(A)-containing retrotransposons. Computer analysis showed that the Penelope protein possesses a reverse transcriptase domain and that its C-terminal domain is an endonuclease similar to bacterial UvrC and endonucleases encoded by group I introns. Such endonuclease has thus far not been predicted for any other known retrotransposon. Multiple sequence alignment with the putative catalytic domain of the Penelope protein revealed five conserved motifs and all essential catalytic residues characteristic of GIY-YIG endonucleases. Experiments have shown that Penelope indeed codes for a functional endonuclease, which is, to an extent, specific to a natural Penelopeinsertion site. |
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