Rana Pol III: A family of SINE-like sequences in the genomes of western Palearctic water frogs

The highly repetitive Rana/Pol III family consists of short, tandemly array ed sequences, scattered throughout the genomes of Palearctic green water fr ogs. The repeat unit is about 250 bp in length and is a composite element: it contains a SINE-like retroposon with a tRNA structure, flanked by two sh ort direct repeats, and the occurrence of two internal repeats gives eviden ce that an additional transposition event may have inserted a segment withi n the already transposed element. Rana/Pol III family is present in the gen omes of Rana lessonae, R. ridibunda, and their hybrid form R. esculenta, as well as in R. shqiperica, R. epeirotica, R, cretensis, and the Italian tax on. These sequences are also present in the Iberian R. perezi, although les s abundant, but appear to be lacking in the north African species R. sahari ca. The distribution of Rana/Pol III in the genomes of Palearctic green fro gs is in agreement with the phyletic history based on genetic data. The evo lutionary pattern proposed for the genus Rana enables us to suppose that th e hybridogenetic mechanism is one of the factors accounting for the possibl e horizontal transfer of Rana/Pol III elements from the central-north Europ e species to R. perezi.