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Mol Cell Biol, February 1998, p. 919-925, Vol. 18, No. 2
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Plasmodium falciparum Telomerase: De Novo Telomere Addition to Telomeric and Nontelomeric Sequences and Role in Chromosome Healing

Emmanuel Bottius, Nassera Bakhsis, and Artur Scherf*

Unité de Parasitologie Expérimentale, CNRS URA 1960, Institut Pasteur, 75724 Paris, France

Received 10 July 1997/Returned for modification 9 September 1997/Accepted 31 October 1997

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 unknown. In this study, telomerase activity has for the first time been identified 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. The sequence GGGTT... was the predominant initial DNA sequence added to the nontelomeric 3' ends in vitro. Poly(C) at the 3' end of the oligonucleotide significantly alters the precision of the new telomerase added repeats. The efficiency of nontelomeric primer elongation was dependent on the presence of a G-rich cassette upstream of the 3' terminus. Oligonucleotide primers based on natural P. falciparum chromosome breakpoints are efficiently used as telomerase substrates. These results imply that P. falciparum telomerase contributes to chromosome maintenance and to de novo telomere formation on broken chromosomes. Reverse transcriptase inhibitors such as dideoxy GTP efficiently inhibit P. falciparum telomerase activity in vitro. These data point to malaria telomerase as a new target for the development of drugs that could induce parasite cell senescence.

* Corresponding author. Mailing address: Unité de Parasitologie Expérimentale, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris Cedex 15, France. Phone: 33-1-45688616. Fax: 33-1-40613185. E-mail: ascherf{at}pasteur.fr.




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