Two variants of the Drosophila melanogaster retrotransposon gypsy ( mdg4 ): structural and functional differences, and d
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O R I GI N A L P A P E R
N. V. Lyubomirskaya á J. B. Smirnova O. V. Razorenova á N. N. Karpova á S. A. Surkov S. N. Avedisov á A. I. Kim á Y. V. Ilyin
Two variants of the Drosophila melanogaster retrotransposon gypsy (mdg4 ): structural and functional differences, and distribution in ¯y stocks Received: 3 March 2000 / Accepted: 22 November 2000 / Published online: 23 February 2001 Ó Springer-Verlag 2001
Abstract Two variants of the Drosophila melanogaster retrotransposon gypsy were subjected to detailed structural and functional analysis. A series of hybrid constructs containing various combinations of ``active'' and ``inactive'' gypsy copies were tested for their ability to produce new DNA copies in cultured cells by means of reverse transcription. It was shown that the previously demonstrated variations in retrotranspositional activity are associated with either one or both of two amino acid substitutions at the beginning of ORF2. The ®rst substitution is located at the boundary between the putative protease and reverse transcriptase domains and, hence, may in¯uence the processing of the polyprotein. The other substitution may alter reverse transcriptase activity since it is located in the second of the seven conserved domains of the RT gene. To address the question of the evolutionary relationship between the two gypsy variants, their distribution was analyzed in among various ¯y stocks. Southern analysis revealed that all D. melanogaster strains studied so far contain the ``inactive'' gypsy variant, while the ``active'' copies are present only in some strains; most of the latter were established from ¯ies recently isolated from natural populations. Finally, in stocks carrying the ¯amenco mutation the ``active'' gypsy variant is much more abundant than the ``inac-
Communicated by G. P. Georgiev N. V. Lyubomirskaya á J. B. Smirnova á S. A. Surkov S. N. Avedisov á Y. V. Ilyin (&) V. A. Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Vavilov St. 32, 117984 Moscow, Russia E-mail: [email protected] O. V. Razorenova á N. N. Karpova á A. I. Kim Department of Genetics, Faculty of Biology, M. V. Lomonosov Moscow State University, Vorob'evy Hills, 119899 Moscow, Russia
tive'' form. Possible scenarios for the origin of the ``active'' form of gypsy are discussed. Key words Drosophila melanogaster á Genetic instability á Retrotransposon á gypsy (mdg4)
Introduction Retrotransposons are mobile genetic elements that constitute a substantial part of the eukaryotic genome. Gypsy (mdg4) is one of the most thoroughly studied retrovirus-like retrotransposons in Drosophila melanogaster. Transposition of gypsy involves reverse transcription, and its structure (Modolell et al. 1983; Bayev et al. 1984; Marlor et al. 1986; Arkhipova et al. 1995) and the main steps in its life cycle have been well characterized (Arkhipova et al. 1986). This element plays an important role in the genetically unstable Mutator Strain (MS) (Kim et al. 1989; Lyubomirskaya et al. 1990), in which its transposition occurs at
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