A new planarian extrachromosomal virus-like element revealed by subtraction hybridization

A combination of suppression subtraction hybridization (SSH) and a new technique of mirror orientation selection (MOS) was used to compare the total DNA for two, sexual (SR) and asexual (AR), races of freshwater planarian Giradia tigrina. Several race-specific DNA fragments were found. A new element termed planarian extrachromosomal virus-like element (PEVE) was revealed in AR. The PEVE genome contains two unique regions, Ul and Us, which are flanked by inverted repeats. Two variants observed for the PEVE genome differ in combination of single- and double-stranded regions corresponding to Ul and Us. The PEVE genome codes for two helicases, one homologous to the circovirus replication initiation protein (Rep) and one corresponding to the helicase domain of papillomavirus E1. PEVE is nonuniformly distributed though the planarian body and is possibly replicated only in certain parenchymal cells.