Isolation of a novel Plasmodium falciparum gene encoding a protein homologous to the Tat-binding protein family

Abstract

We have cloned a Plasmodium falciparum gene that belongs to the nuclear Tat-binding protein (TBP) gene family. This gene, PfTBP, is (A + T)-rich and encodes a 49.5-kDa protein. The predicted protein encoded by this gene has highest similarity to the slime mold protein DdTBP10 (86%) and to the yeast protein SUG1 (81.8%), both of which belong to the Tat-binding protein family. In agreement with the characteristics of this family, PfTBP contains a highly conserved domain of approximately 200 amino acids, in which are found the motifs A and B of ATPases, and amino acid sequences characteristic of a large family of RNA or DNA helicases, suggesting a role in RNA or DNA unwinding. Like DdTBP10, the PfTBP protein has a heptad repeat of four leucine residues, reminiscent of a leucine zipper motif known to mediate dimerization. We have further characterized PfTBP gene expression by Northern-blot analysis. This gene is expressed in a stage-specific manner, with higher expression in the late trophozoite stage. The recombinant PfTBP gene has been expressed in Escherichia coli and a polyclonal antiserum has been raised in rabbits against the recombinant protein. This antibody has been used to study the protein in the parasite. The gene product is expressed in a stage-specific manner with higher expression in the late trophozoite and schizont stages, and is localized in the nucleus of the erythrocytic stage parasite. Thus the protein might have a function in DNA synthesis and/or in transcription, as is the case for other Tat-binding proteins.