A mouse type 2 Alu sequence (M2) is mobile in the genome

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Abstract
The Alu and its equivalent families of interspersed repetitive DNA sequences have been found in various mammalian genomes. It has been proposed that some of them might move around the genome like known prokaryotic and eukaryotic transposable elements, as most of these sequences are flanked by short direct repeats at both ends. To prove that this is the case, however, one must demonstrate the existence of homologous sequences of DNA with and without Alu insertion among the genomes of different strains or individuals of a species. While studying a polymorphic repetitive sequence (PR1) originally found in the spacer region of mouse ribosomal RNA genes, we have now found that a sequence similar to the CHO type 2 Alu-equivalent element, designated M2, is inserted within a PR1 sequence which is located outside the ribosomal RNA gene and that this M2 segment is flanked by a short direct repeat at both ends. Furthermore, this PR1 segment containing M2 is detected only in the BALB/c strain among the laboratory mice and wild mouse subspecies examined. These facts suggest that the M2 sequence has been inserted into PR1 sequence relatively recently during evolution of mouse strains and support the idea that at least some of the Alu-equivalent families are mobile in the genome. Recently, Grimaldi and Singer reported an African green monkey alpha-satellite sequence that was interrupted by an Alu element.