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 investigat ed for the gene encoding Plasmodium falciparum topoisomerase II (PfTop oII). Nuclear run-on experiments have shown that the P. falciparum top oisomerase II gene (PfTOP2) promoter is active at low levels in ring s tage parasites, but reaches high levels of activity as the parasites p rogress into trophozoite/schizont asexual stages. Steady-state PfTOP2 transcripts are present at low levels in rings, accumulate in trophozo ites, but are completely undetectable in schizonts. An antiserum raise d against the species-divergent carboxy-terminus of PfTo-poII, which n eutralised 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 compare d with those in trophozoite and schizont preparations. Parasite extrac ts 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 l evels. These finding show that, as parasites progress towards the stag es where DNA replication occurs, there is a concomitant increase in bo th topoisomerase II production and activity. (C) 1998 Elsevier Science B.V. All rights reserved.