HETEROGENEITY OF THE RIBOSOMAL DNA EPISOME IN STRAINS AND SPECIES OF ENTAMOEBA

Ribosomal DNA sequences in several species of the genus Entamoeba are highly repeated and display restriction fragment-length polymorphism ( RFLP), which has been used to identify species and differentiate strai ns. However, the continuous variability of the non-transcribed repeat sequences in the ribosomal episome hinders an accurate typification. L ooking for :more reliable markers, we used DNA probes containing conse rved sequences in the ribosomal episome - coding regions for the 16S a nd 5.8S rRNAs and transcribed spacers flanking the rDNA sequences, and the coding region for the 3' end of the 26S rRNA - to analyse hybridi zation patterns from five cloned pathogenic strains of Entamoeba histo lytica, two strains of the also pathogenic Entamoeba invadens and the non-pathogenic Laredo strain of Entamoeba moshkovskii. Our results pro vide reliable bases for the differentation of clones, strains and spec ies of Entamoeba and the reconstruction of E. histolytica episomes. Di fferences in the number and length of rDNA-containing DNA fragments, p reviously observed by other investigators and confirmed by us, can be better defined by the present analysis.