Isolation and characterization of a species-specific multicopy DNA sequence from Entamoeba histolytica

A genomic library of Entamoeba histolytica (pathogenic strain HM-1:IMSS) was screened to detect repetitive DNA clones other than those from the highly abundant ribosomal DNA (rDNA). One such clone (HMc) had a 2.3 kb insert which hybridized with the main genome and not the rDNA circle. Southern hybridization of E. histolytica genomic DNA, digested with EcoR I and probed with HMc, showed multiple bands. The banding pattern was identical in all axenic pathogenic strains tested. Differences, however, existed when the banding pattern of a pathogenic strain was compared with that of a non-pathogenic strain. HMc was present in about 25-30 copies per genome in strain HM-1:IMSS. Nucleotide sequence analysis of HMc revealed a partial open reading frame which hybridized with a 1.35 kb poly A+ transcript in Northern blots. The deduced amino acid sequence did not, however, show significant homology with known proteins. The HMc sequence was found only in E. histolytica as it hybridized with 5 different axenic strains of E. histolytica but did not recognize other closely related species of Entamoeba. It has thus the potential to be used as a species-specific DNA probe.