The ribosomal intergenic spacer (IGS) region in Schistosoma japonicum: structure and comparisons with related species.

The intergenic spacer (IGS) between the 28S and 18S ribosomal RNA genes was PCR-amplified, sequenced and characterized for Schistosoma japonicum from mainland China, and compared with those of other Schistosoma species. Excluding flanking portions of the 28S and 18S genes, the IGS in the longest sequenced amplicon from S. japonicum IGS was 1457bp in length. However, intra-specific and intra-individual variation was noted. The IGS region of S. japonicum is strikingly different in structure from those of African Schistosoma species for which data are available. S. japonicum has a shorter IGS and largely lacks a long region of complex repeats seen in the African species. However, careful comparisons with African species highlighted the presence of a few shared repeat motifs that were not apparent from study of African species only. Such motifs presumably have functional significance. Discovery of such motifs may in general be aided by comparisons of relatively distant taxa rather than of sibling taxa.