CORE-SINEs: Eukaryotic short interspersed retroposing elements with commonsequence motifs

A 65-bp "core" sequence is dispersed in hundreds of thousands copies in the human genome. This sequence was found to constitute the central segment of a group of short interspersed elements (SINEs), referred to as mammalian-w ide interspersed repeats, that proliferated before the radiation of placent al mammals, Here, we propose that the core identifies an ancient tRNA-like SINE element, which survived in different lineages such as mammals, reptile s, birds, and fish, as well as mollusks, presumably for >550 million years, This element gave rise to a number of sequence families (CORE-SINEs), incl uding mammalian-wide interspersed repeats, whose distinct 3 ' ends are shar ed with different families of long interspersed elements (LINEs), The evolu tionary success of the generic CORE-SINE element can be related to the recr uitment of the internal promoter from highly transcribed host RNA as well a s to its capacity to adapt to changing retropositional opportunities by seq uence exchange with actively amplifying LINEs. It reinforces the notion tha t the very existence of SINEs depends on the cohabitation with both LINEs a nd the host genome.