Plasmodium falciparum: Stage-related expression of topoisomerase I

The expression and activity of topoisomerase I (PfTopoI) has been examined during the intraerythrocytic stages of the Plasmodium falciparum life cycle . The promoter is inactive during the early ring stage and becomes active o nly during the later trophozoite and schizont stages. The PfTOP1 transcript starts to accumulate in the trophozoite stage parasite, decreasing again i n the schizont stage. Using both stage-specific Western analysis and immuno fluorescent assays we show that PfTopoI is present at low levels in rings a nd accumulates to approximately equal levels in the trophozoite and schizon t stages. Experiments to determine the activity of PfTopoI, using a topoiso merase I relaxation assay, show that then is a low level of PfTopoI activit y in both ring and trophozoite stages, but activity increases dramatically in the schizont stage. The PfTopoI activity can be inhibited by treatment w ith specific antiserum and by the type I topoisomerase-specific inhibitor c amptothecin, (C) 1999 Academic Press.