SINE Cousins: The 3'-End Tails of the Two Oldest and Distantly Related Families of SINEs are Descended from the 3' Ends of LINEs with the Same Genealogical Origin

Abstract

AFC short interspersed elements (SINEs) were isolated from cichlids from Madagascar, the New World, and Africa and characterized. A new family of long interspersed elements (LINEs), designated the CiLINE2 family, was also isolated from African cichlids, and its consensus sequence was deduced. Upon aligning all of the consensus sequences, we found that the 3'-tail regions of the AFC SINEs and the CiLINE2 family were very similar, providing another example in which a reverse transcriptase responsible for retroposition of SINEs might be contributed in trans by a LINE. Sequence comparisons showed that CiLINE2 in cichlids was closely related to LINE2 in mammals. Furthermore, we found that the 3'-tail sequence shared by the AFC SINEs and CiLINE2 in cichlids was very similar to the 3'-tail sequence shared by the MIR SINEs and LINE2 in mammals, even though the remaining parts of the AFC SINEs and the MIR SINEs were totally different from each other. Thus, the present report not only describes a new pair of SINEs and LINEs with the same 3' tail in cichlids, but also provides a new example of the phenomenon whereby the 3' ends of LINEs with the same genealogical origin can be incorporated into the 3'-end tails of different families of SINEs that have been generated independently in two different lineages during evolution.