Article
Useful 'junk': Alu RNAs in the human transcriptome
HASLER, Julien, SAMUELSSON, T, STRUB, Katharina
Abstract
Alu elements are the most abundant repetitive elements in the human genome; they have amplified by retrotransposition to reach the present number of more than one million copies. Alu elements can be transcribed in two different ways, by two independent polymerases. 'Free Alu RNAs' are transcribed by Pol III from their own promoter, while 'embedded Alu RNAs' are transcribed by Pol II as part of protein- and non-protein-coding RNAs. Recent studies have demonstrated that both free and embedded Alu RNAs play a major role in post transcriptional regulation of gene expression, for example by affecting protein translation, alternative splicing and mRNA stability. These discoveries illustrate how a part of the 'junk DNA' content of the human genome has been recruited to important functions in regulation of gene expression.
Reference
HASLER, Julien, SAMUELSSON, T, STRUB, Katharina. Useful 'junk': Alu RNAs in the human transcriptome. Cellular and Molecular Life Sciences, 2007, vol. 64, no. 14, p. 1793-800
DOI : 10.1007/s00018-007-7084-0 PMID : 17514354
Available at: http://archive-ouverte.unige.ch/unige:17489
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1 / 1 Cell. Mol. Life Sci. DOI 10.1007/s00018-007-7084-0 Cellular and Molecular Life Sciences Birkh user Verlag, Basel, 2007
Visions & Reflections (Minireview)
Useful junk : Alu RNAs in the human transcriptome
J. H sler a, T. Samuelsson b and K. Strub a, * aD partement de Biologie Cellulaire, 30 quai Ernest Ansermet 1211 Geneve-4 (Switzerland), Fax : +41223796442, e-mail: [email protected] bGçteborg University, Institute of Biomedicine, Department of Medical Biochemistry and Cell Biology, Box 440, 405 30 Gçteborg (Sweden)
Received 16 February 2007; received after revision 28 March 2007; accepted 25 April 2007
Abstract. Alu elements are the most abundant repet- cent studies have demonstrated that both free and itive elements in the human genome; they are embedded Alu RNAs play a major role in post- amplified by retrotransposition to reach the present transcriptional regulation of gene expression, for number of more than one million copies. Alu elements example by affecting protein translation, alternative can be transcribed in two different ways, by two splicing and mRNA stability. These discoveries illus- independent polymerases. Free Alu RNAs are tran- trate how a part of the junk DNA content of the scribed by Pol III from their own promoter, while human genome has been recruited to important embedded Alu RNAs are transcribed by Pol II as functions in regulation of gene expression. part of protein- and non-protein-coding RNAs. Re-
Keywords. Alu elements, Alu RNA, Alu RNP, alternative splicing, A-to-I editing, translation regulation, miRNAs, UTR, gene expression.
Introduction elements are specific to primates; they emerged more than 55 million years ago from the 7SL RNA gene, In 2001, the completion of the human genome which encodes the RNA moiety of the signal recog- sequencing revealed that less than 2% of its nucleotide nition particle (SRP) [2, 3]. Alu elements amplified sequence code for proteins, while 55% of its mass are via RNA intermediates by a mechanism of retrotrans- exclusively composed of repetitive elements [1]. With position that is currently under investigation. As they more than 1 million copies, Alu elements are the most do not encode any protein, their amplification has abundant repetitive elements in the human genome; probably been dependent on the transposition machi- altogether, they represent about 10% of the genome nery of other retrotransposing elements, and it has mass and belong to the SINE (short interspersed recently been shown that they could use LINE-1 elements) family of repetitive elements. elements for this purpose [4]. Very few Alu elements Modern Alu elements are approximately 300 bp in are able to retrotranspose; they emerged from a length and have a dimeric structure. They are com- limited number of loci that are considered as master posed of two similar but distinct monomers (left and genes