Figure 1

Phylogenetic tree and schematic drawing of the gene structure of the sushi-ichi retrotransposon gene and the mouse Mart genes. A) Phylogenetic and DNA sequence analysis indicates that the Mart gene family originated independently several times in the ancestors of placentalia. Long distances of the lines between single genes represent greater DNA differences, for example Zcchc16/Mart4 is considered an outgroup from all other Mart genes. On the other hand, Cxx1a,b/Mart8b,c belong to one gene clade, whereas Cxx1c/Mart8a is on a different gene clade, which is ancestral to Cxx1a /Mart8b and Cxx1b/Mart8c. Therefore Cxx1c/Mart8a could be the first evolutionary Cxx1/Mart8 gene integrated into the genome, whereas Cxx1a/Mart8b and Cxx1b/Mart8c later duplicated events. B) Listed is the first founded sushi-ichi retrotransposon from Puffer fish and then the eleven mouse Mart genes. Numbers indicate amino acid lengths of proteins and colored boxes symbolize the different protein motifs identified as the gag (group specific antigen), pro (protease), pol (polymerase) and int (integrase). The arrow on the Peg10/Mart2 protein points to the −1 frame shift, which results in two open reading frames (RF1 and RF2).