PLASMODIUM-FALCIPARUM TELOMERASE - DE-NOVO TELOMERE ADDITION TO TELOMERIC AND NONTELOMERIC SEQUENCES AND ROLE IN CHROMOSOME HEALING

Telomerase, a specialized cellular reverse transcriptase, compensates for chromosome shortening during the proliferation of most eucaryotic cells and contributes to cellular immortalization. The mechanism used by the single-celled protozoan malaria parasite Plasmodium falciparum to complete the replication of its linear chromosomes is currently unk nown. In this study, telomerase activity has for the first time been i dentified in cell extracts of P. falciparum. The de novo synthesis of highly variable telomere repeats to the 3' end of DNA oligonucleotide primers by plasmodial telomerase is demonstrated. Permutated telomeric DNA primers are extended by the addition of the next correct base. In addition to elongating preexisting telomere sequences, P. falciparum telomerase can also add telomere repeats onto nontelomeric 3' ends. Th e sequence GGGTT was the predominant initial DNA sequence added to the nontelomeric 3' ends in vitro. Poly(C) at the 3' end of the oligonucl eotide significantly alters the precision of the new telomerase added repeats. The efficiency of nontelomeric primer elongation was dependen t on the presence of a G-rich cassette upstream of the 3' terminus. Ol igonucleotide primers based on natural P. falciparum chromosome breakp oints are efficiently used as telomerase substrates. These results imp ly that P. falciparum telomerase contributes to chromosome maintenance and to de novo telomere formation on broken chromosomes. Reverse tran scriptase inhibitors such as dideoxy GTP efficiently inhibit P. falcip arum telomerase activity in vitro. These data point to malaria telomer ase as a new target for the development of drugs that could induce par asite cell senescence.