The malaria parasite Plasmodium falciparum encodes members of the Puf RNA-binding protein family with conserved RNA binding activity

A novel class of RNA-binding proteins, Puf, regulates translation and RNA stability by binding to specific sequences in the 3'-untranslated region of target mRNAs. Members of this protein family share a conserved Puf domain consisting of eight 36 amino acid imperfect repeats. Here we report two Puf family member genes, PfPuf1 and PfPuf2, from the human malaria parasite Plasmodium falciparum. Both genes are spliced with four and three introns clustered within or near the Puf domains, respectively. Northern and RT-PCR analysis indicated that both genes were differentially expressed in gametocytes during erythrocytic development of the parasite. Except for similarities in the Puf domain and expression profile, the deduced PfPuf1 and PfPuf2 proteins differ considerably in size and structure. PfPuf1 has 1894 amino acids and a central Puf domain, whereas PfPuf2 is much smaller with a C-terminal Puf domain. The presence of at least two Puf members in other Plasmodium species suggests that these proteins play evolutionarily similar roles during parasite development. Both in vivo studies using the yeast three-hybrid system and in vitro binding assays using the recombinant Puf domain of PfPuf1 expressed in bacteria demonstrated intrinsic binding activity of the PfPuf1 Puf domain to the NRE sequences in the hunchback RNA, the target sequence for Drosophila Pumilio protein. Altogether, these results suggest that PfPufs might function during sexual differentiation and development in Plasmodium through a conserved mechanism of translational regulation of their target mRNAs.