Intraerythrocytic expression of topoisomerase II from Plasmodium falciparum is developmentally regulated

The stage-specific relationship between promoter activity, transcript production, protein expression and enzyme activity has been investigated for the gene encoding Plasmodium falciparum topoisomerase II (PfTopoII). Nuclear run-on experiments have shown that the P. falciparum topoisomerase II gene (PfTOP2) promoter is active at low levels in ring stage parasites, but reaches high levels of activity as the parasites progress into trophozoite/schizont asexual stages. Steady-state PfTOP2 transcripts are present at low levels in rings, accumulate in trophozoites, but are completely undetectable in schizonts. An antiserum raised against the species-divergent carboxy-terminus of PfTopoII, which neutralised the decatenation activity in parasite extracts, was used to probe Western blots of ring, trophozoite and schizont stage parasite extracts. Relatively low levels of PfTopoII were seen in rings compared with those in trophozoite and schizont preparations. Parasite extracts were also used to compare the patterns of protein accumulation and enzyme activity at these stages. Complete decatenation of kinetoplast substrate DNA (KDNA) was found in schizont stages, very low levels of activity were observed in rings and trophozoites showed intermediate levels. These finding show that, as parasites progress towards the stages where DNA replication occurs, there is a concomitant increase in both topoisomerase II production and activity.