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Integration specificity of the mobile element Tirant in the Drosophila melanogaster genome Lidia N. Nefedova, A.O. Shmel'kova, A.R. Lavrenov, F.A. Urusov, N.I. Romanova, Alexander I. Kim
Department of Genetics, Moscow State University, Moscow, 119992 Russia, aikim57@mail.ru

Mobile genetic elements (MGEs) account a significant part of the eukaryotic geno me. Their transposit ion has a wide range of phenotypic expressio n and proved to be one of the most important mechanisms o f the evo lutionary process. The geno me o f the model object Drosophila melanogaster, since it contains a wide variet y of the MGEs differed by the structure and mo vement characterist ics, is widely used to study the mechanisms o f the regulat ion and the evolut ionary significance of transposit io n. The choose of target sites for the MGE integratio n is influenced by a number o f factors, including the structure of the target DNA, DNA methylat ion and transcript ion status, integrase features and others. It has been found that the transposition o f the D. melanogaster MGEs of the gypsy group occurs to the specific target sites with the determined nucleotide sequence. Among these MGEs, ZAM and Titant recognize target site 5'-CGCGCG-3' [1]. Besides, the transposit ion o f the ZAM element occurs mainly in the heterochromatic regio ns and is regulated by interact ion o f its 5'-untranslated region wit h the heterochromat in protein Hp1a [2]. Since the MGE Tirant is close to ZAM in phylogenet ic terms, we suggested that the regulat ion of its transposit ion may also be carried out through the interaction wit h the Hp1a protein Wit h use o f the sequenced geno me of D. melanogaster, available in the FlyBase database, we have determined that all transposit ions of the MGE Tirant occurs in euchro mat in and predominant ly in introns of genes or in areas adjacent to genes, which are characterized by a high level of transcription in the early stages o f development. In the 5'untranslated regio n Tirant 102 bp tandem repeats are indentified, and their number may var y fro m 3 to 6. Most of the Tirant copies have 5-6 repeats, and this observat ion allows us to put forward the assumption that copies wit h the greater number o f repeats have the select ive

advantage. This assumpt ion is confirmed experimentally. It is noteworthy that the ident ified repeats form open reading frame and in a hypothet ical translat ion show ho mo logy to the tetratricopeptide repeat domain (TRP) detected in the structure of a number o f regulatory proteins. We characterized D. melanogaster genes, in which sequences the insertions of Tirant were detected, by their abilit y to interact with protein Hp1a. For this experiment, we used data of the modENCODE pro ject (Geno me-wide Chromatin Profiling in Drosophila), performed on Affymetrix microchips. As a result, we found that most of the analyzed genes do not interact with Hp1a on embryo nic and larval stages; this corresponds to the data on their expressio n. On the adult stage, these genes have a very low level o f expression or no expressio n. This fact coincides wit h the results of microarray analys is detected their interact ion with Hp1a on the adult stage. The same pattern of expressio n and interact ion wit h Hp1a was found for the aralar and cactus genes, in which introns Tirant de novo insertions have been detected in our laboratory. Thus, the MGE Tirant transposes, apparent ly, on the early stages o f D. melanogaster development, when the majorit y o f it s target sequences are not associated with Hp1a and expressed at high level. The lack o f associat ion wit h the Hp1a protein is a necessar y condit ion for the Tirant integration. The presence of tandem repeats in the 5'-untranslated region and the select ion to ward increasing their number may both indicate the existence of an alternat ive mechanis m of Tirant integrat ion using repeats to facilitate contact with the DN A targets either through their inclusio n as a part of own proteins or by direct interaction wit h host proteins. The work was supported by RFBR (grant 11-04-00403-).

1. L.N.Nefedova et al. (2011) Integration specificit y o f LTR retrotransposons and retroviruses in the Drosophila melanogaster genome. Virus Genes, 42(2):297306. 2. C.Minervini et al. (2007) Heterochromatin protein 1 interacts with 5UTR of transposable element ZAM in a sequence-specific fashio n, Gene, 393: 110.