A Dimeric SINE Discovered in Shrew Mole is Structurally Similar to Primate Alu
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Families of Short Interspersed Elements (SINEs) originate from tRNA, 5S rRNA, and 7SL RNA molecules in the genomes of multicellular organisms. Families of 7SL RNA-derived SINEs are very rare; however, they have been best studied in primates and rodents. The rodent B1 SINE is a monomeric element, whereas the primate Alu is composed of two 7SL RNA-derived monomers.We found that in contrast to other members of the family Talpidae (moles), which possess a tRNA-derived Tal SINE, the shrew mole Uropsilus gracilis contains 280,000 genomic copies of the previously unknown 7SL RNA-derived Urop SINE. Like Alu, Urop consists of two monomers connected by an A-rich linker. The origin of the Urop monomers, like that of the Alu and B1 monomers, was mediated by several essentially identical events - a long central deletion in the 7SL RNA, dimerization, and/or internal duplication. Urop copies can be divided into three subfamilies (a, b, and c), the latter being the most numerous and recent. Urop_c has more copies with poly(A) tails longer than 50 compared to other L1-mobilized SINEs. Urop and Alu illustrate an independent emergence in the evolutionary history of highly similar SINEs.
