Sines

SINES (Short Interspersed Nuclear Elements) are types of retrotransposons (also called transposons via RNA intermediates) and are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms.

SINEs

Short interspersed elements are short DNA sequences (<500 bases) that represent reverse-transcribed RNA molecules originally transcribed by RNA polymerase III into tRNA, rRNA, and other small nuclear RNAs. SINEs do not encode a functional reverse transcriptase protein and rely on other mobile elements for transposition. The most common SINEs in primates are called Alu sequences. Alu elements are 280 base pairs long, do not contain any coding sequences, and can be recognized by the restriction enzyme AluI (hence the name). With about 1,500,000 copies, SINEs make up about 11% of the human genome. While historically viewed as "junk DNA", recent research suggests that in some rare cases both LINEs and SINEs were incorporated into novel genes, so as to evolve new functionality. The distribution of these elements has been implicated in some genetic diseases and cancers.

SINEs are short DNA sequences (100–400 base pairs) that represent reverse-transcribed RNA molecules originally transcribed by RNA polymerase III; that is, molecules of tRNA, 5S rRNA, and some other small nuclear RNAs.

The most abundant SINEs are the Alu elements. There are over one million copies in the human genome (representing 9% of our total DNA).

Alu elements consist of a sequence averaging 260 base pairs that contains a site that is recognized by the restriction enzyme AluI. They appear to be reverse transcripts of 7S RNA, part of the signal recognition particle.

Most SINEs do not encode any functional molecules and depend on the machinery of active L1 elements to be transposed; that is, copied and pasted in new locations.

Retrotransposons, also known as class I transposable elements, consist of two subclasses, the long terminal repeat (LTR-retrotransposons) and the non-LTR retrotransposons

LTR retrotransposons have direct LTRs that range from ~100 bp to over 5 kb in size. LTR retrotransposons are further sub-classified into the Ty1-copia-like (Pseudoviridae), Ty3-gypsy-like (Metaviridae), and BEL-Pao-like groups based on both their degree of sequence similarity and the order of encoded gene products.