A TANDEMLY REPEATED DNA FAMILY ORIGINATED FROM SINE-RELATED ELEMENTS IN THE EUROPEAN PLETHODONTID SALAMANDERS (AMPHIBIA, URODELA)

We have characterized a highly repetitive family, named Hy/Pol III, in the genome of the European salamanders Hydromantes (Plethodontidae). This family consists of short, tandemly repeated sequences organized in clusters, scattered through the genome as shown both by in situ hybridization to chromosomes and by Southern blot hybridization. The repeat unit is about 200 bp in length and it is a composite element since it contains a SINE-like retroposon with a tRNA structure, flanked by two short direct repeats. The whole element itself is bordered by two other direct repeats. The sequence data suggest that two elements, presumably derived from polymerase III transcripts, have been inserted one into the other, giving rise to the observed composite structure. During evolution the Hy/Pol III family was then amplified by tandem duplication at the DNA level. The inferred relationships between Hy/Pol III members from three representative species of the European Hydromantes suggests that a subfamily structure characterizes the evolutionary history of this family.