Short interspersed nuclear element

Short Interspersed Nuclear Elements (SINEs) are non-autonomous, non-coding transposable elements (TEs) that are 50-500 base pairs long. The internal regions of SINEs originate from tRNA and remain highly conserved, suggesting positive pressure to preserve structure and function of SINEs. While SINEs are present in many species of vertebrates and invertebrates, SINEs are often lineage specific, making them useful markers of divergent evolution between species. Copy number variation and mutations in the SINE sequence make it possible to construct phylogenies based on differences in SINEs between species. SINEs are also implicated in certain types of genetic disease in humans and other eukaryotes.

SINEs are classified as non-LTR retrotransposons because they do not contain long terminal repeats (LTRs). There are three types of SINEs common to vertebrates and invertebrates: CORE-SINEs, V-SINEs, and AmnSINEs. SINEs have 50-500 base pair internal regions which contain a tRNA-derived segment with A and B boxes that serve as an internal promoter for RNA polymerase III.

SINEs use an RNA intermediate and reverse transcriptase to transpose into new parts of the genome. SINEs do not encode a functional reverse transcriptase and have to rely on the molecular machinery of other TEs for transposition. SINEs and other nuclear elements rely on the LINE-1 (L1) proteins for transposition throughout the genome. L1 is transcribed and retrotransposed most frequently in the germ-line and during early development; as a result SINEs move around the genome most during these periods. SINE transcription is down-regulated by transcription factors in somatic cells after early development, though stress can cause up-regulation of normally silent SINEs. SINEs can be transferred between individuals or species via horizontal transfer though a viral vector.

...
Wikipedia