Sjα elements, short interspersed element-like retroposons bearing a hammerhead ribozyme motif from the genome of the Oriental blood fluke Schistosoma japonicum

Abstract

Smα is a short interspersed element (SINE)-like retroposon that occurs in high copy number of the genome of the human blood fluke Schistosoma mansoni. The sequence of the consensus Smα element includes the hallmark features of SINE-like elements including a promoter region for RNA polymerase III, an AT-rich stretch at its 3′-terminus, a short length of 500 bp or less, and short direct repeat sequences flanking the insertion site. Interestingly, the sequence of Smα also encodes an active ribozyme bearing a hammerhead domain. Contrary to the recent findings of Ferbeyre et al. ( Mol. Cell. Biol. 18 (1998) 3880-8) that indicated that Smα-like elements were absent from the genome of the Oriental blood fluke Schistosoma japonicum, we report here that the genome of S. japonicum does contain a family of Smα-like retroposons, elements that we have named the Sjα family. Like Smα, Sjα elements are SINE-like in structure and sequence, are present at high copy number interspersed throughout the S. japonicum genome, and contain an ostensibly functional, hammerhead ribozyme motif. The presence of these elements in all species of Schistosoma so far examined suggests that the hammerhead domain was acquired by vertical transmission from a common schistosome ancestor.