A NOVEL CYTOPLASMIC STRUCTURE CONTAINING DNA NETWORKS IN ENTAMOEBA-HISTOLYTICA TROPHOZOITES

We report here the presence of cytoplasmic DNA arranged in networks in the trophozoites of the human parasite Entamoeba histolytica. Cytopla smic DNA was detected in live trophozoites in a structure that we call ed EhkO, using the fluorescent dye acridine orange, and by in situ hyb ridization to trophozoites with a rDNA probe. The EhkO was found in th e axenically grown clones A, L6 (strain HM1:IMSS) and MAVax (strain MA V) and in the polyxenically grown clone MAVpx (strain MAV). Bacteria p resent in MAVpx did not cross hybridize with the DNA probe neither in in situ hybridization or in Southern blot experiments. Autoradiography of metabolically [H-3]thymidine-labeled trophozoites showed the prese nce of EhkO, and an EhkO-enriched fraction, purified from a nuclei-fre e extract and examined by light microscopy, exhibited [H-3]thymidine i ncorporation into this structure. DNA was purified from the EhkO and e nriched nuclear fractions and analyzed by transmission electron micros copy. The EhkO fraction contained DNA networks resembling those of try panosome kDNA, whereas nuclear DNA was present mainly as linear molecu les and some circles, Our findings imply that E. histolytica may be ta xonomically more closely related to the Trypanosomatidae than previous ly suspected.