LINE-1 element in the vole Microtus subarvalis.

Abstract

Highly repetitive DNA sequences of the LINE-1 (L1) family, which are interspersed in the genomes of various organisms, are among the many transposable elements deserving attention. L1 elements are widely distributed throughout the mammalian genomes (Burton et al. 1986). Their occurrence was first demonstrated in man and other mammals. Subsequently, L1like elements were found to occur in insects and higher plants (DiNosera and Sakaki 1990). No definite role has yet been assigned to L1 elements. Their presence in virtually all organisms suggests that they might be important for the structural organization and function of the genome. The sequence features of L 1 include two open reading frames (ORFs), the short 5' proximal ORF1 and the about four times longer 3' proximal ORF2. L1 element contains a poly(A) tail at the 3' end and is flanked by short direct repeats (Fanning and Singer 1987). The sequence similarity between L1 and retroviruses and related transposable elements suggests that the predicted ORF2 encoded protein is involved in the transpos i t ion of L1 e lement . The suppor t for the involvement of LI-encoded proteins in L1 transposition has come from in vitro studies (Leibold et al. 1990). More recently it was shown that human L1 element encodes reverse transcriptase activity (Dombroski et al. 1991; Mathias et al. 1991). We describe here genomic L1 element detected in voles of the Microtus genus. Genomic DNA was prepared from vole liver according to standard procedures (Henry et al. 1990); complete digestion was performed with endonuclease EcoRI. Comparative restriction analysis of genomic DNAs from five vole species is shown in Fig. 1. Clearly, the number and distribution of bands corresponding to DNA repeats are specific to each of the species. The intense band is common to the four species, and it represents the same