Inter- and intra-strain variation in the 5.8S ribosomal RNA and internal transcribed spacer sequences of Entamoeba histolytica and comparison with Entamoeba dispar, Entamoeba moshkovskii and Entamoeba invadens.

The ribosomal RNA genes in Entamoeba histolytica are located on circular DNA molecules in about 200 copies per genome equivalent. Nucleotide sequence analysis of the 5.8S rRNA gene and the flanking internal transcribed spacers was carried out to determine the degree of sequence divergence in the multiple rRNA gene copies of a given strain; amongst three different E. histolytica strains (HM-1:IMSS, Rahman and HK-9); and amongst four species of Entamoeba (Entamoeba histolytica, Entamoeba dispar, Entamoeba moshkovskii and Entamoeba invadens). The results show that all rRNA gene copies of a given strain are identical. Few nucleotide positions varied between strains of a species but the differences were very pronounced amongst species. In general, the internal transcribed spacer 2 sequence was more variable and may be useful for strain- and species-identification. The 5.8S rRNA gene and the internal transcribed spacer 2 of E. invadens were unusually small in size.