Features of the mammal mar1 transposons in the human, sheep, cow, and mouse genomes and implications for their evolution.

Mariner-like elements (MLE) belong to the Tc1/ mariner superfamily of class II transposons. We have analyzed the mariner related to the cecropia subfamily, and called mammal mar1, in four mammalian genomes, Bos taurus (Bovidae), Homo sapiens (Primata), Mus musculus (Rodentia), and Ovis aries (Ovidae). Three kinds of MLE sequences were found in all these species: full-length 1.3-kbp elements, shorter elements 80 bp-1.2 kbp, and single inverted terminal repeats (ITRs). All the 1.3-kbp genomic copies sequenced had an open reading frame encoding a transposase interrupted by stop codons or frame shifts. Phylogenetic analysis of the full-length elements suggested at least two distinct populations of mammal mar1 elements in each species. This was confirmed by using a statistical method that allows defining populations. Finally, the evolutionary origin of the mammal mar1 elements and the paradoxes are discussed.