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Retroelements constitute a large fraction of the repetitive DNA of eukaryotic genomes. They include LTR (Long Terminal Repeat) and non-LTR retrotransposons, lacking the long terminal repeats and subdivided into LINEs (Long Interpersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements), have been discovered as ubiquitous components of nuclear genomes in many species. LINEs are able to transpose autonomously, while non-autonomous SINEs depend on the reverse transcription machinery of other retrotransposons. Non-LTR retrotransposons were first discovered in mammalian genomes but have also been identified in plants, fungi and invertebrates. SINEs are a moderately to highly amplified sequence class of Eukaryotes which have been most extensively studied in mammalian species (Alu family). SINEs are up to several hundred basepairs in length (>500 bp) and have a composite structure. The 5' region of SINEs is similar to tRNA (the major class), 5S rRNA or to 7SL RNA genes (the minor classes). The 3' region of many SINEs shows similarity to the 3' end of LINEs. SINEs are terminated by a poly(A) tract or A- or T-rich sequences. Two well conserved sequence motifs are found in the tRNA-related part of SINEs. Similar to tRNA genes, these sequences, called box A and box B, serve as an internal promotor for RNA polymerase III. SINEs do not encode theirown reverse transcriptase and are therefore unable to transpose aitonomously. Similar to LINEs, they move by retrotransposition and generate short target site duplications upon reintegration. Data on possible functions for SINEs are still incomplete and controversial, but it is likely that SINEs have a major impact on their genomes. They have a significant role in genome/gene evolution, structure and transcription levels. The distribution of these elements has been implicated in some genetic diseases and cancers. They are very useful as markers for phylogenetic analysis, becouse species exhibit variation in the genomic localization of SINE inserts.
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Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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