Sines – Interspersed Elements of Eukaryote Genomes

Abstract

SINEs (Short INterspersed Elements or Short Interspersed Nuclear Elements) are a class of dispersed and mobile DNA sequences (less than 500 basepairs (bp) in length) that are propagated through a replicative mechanism called retrotransposition, in which a RNA intermediate is reverse-transcribed into a cDNA that can integrate into the genome. As nonautonomous elements with no coding capability SINEs must use the enzymatic machinery of an autonomous LINE (Long INterspersed Element) partner for retroposition [20]. This SINE-LINE partnership is based on common 3' terminal regions or polyadenylated tails. These interspersed elements are found in essentially all eukaryotic nuclear genomes [5, 17, 19, 22, 23]. Interestingly, SINEs are particularly abundant in mammals accounting for more than 15% of the human genome. All currently known SINEs are derived from tRNA (major classes), 7SL RNA or 5S rRNA (for several mammalian and zebrafish families) genes, and exploit their type 1 or 2 internal polymerase III promoters. Conservation in tRNA-related regions and the internal promoter (composed of A and B motifs) allows recognition by the RNA polymerase III machinery [8]. SINEs are probably mobilized by the retroposition activity of autonomous long interspersed elements (LINEs) and upon integration usually generate a duplication of the genomic target sites. The most extensively characterized SINE families are the human Alu family (the most abundant SINE in the human genome that is amplified to a copy