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RuvB protein belongs to AAA+ family of enzymes involved in diverse cellular activities. In addition to the annotated two RuvB proteins in Plasmodium falciparum database, we report that a third RuvB protein is also present. The amino acid sequence analysis has revealed that P. falciparum RuvB3 (PfRuvB3) possesses Walker motif A, Walker motif B, sensor I and sensor II conserved motifs similar to yeast and human RuvB like proteins. The phylogenetic analysis revealed that PfRuvB3 is closely related to yeast RuvB like proteins which are essential for the survival of yeast. The biochemical characterization of recombinant PfRuvB3 confirms its ssDNA dependent ATPase activity. Using the truncated derivatives we show that Walker motif A is essential for the enzymatic activity of PfRuvB3. Using the immunodepletion assays we further show that the ATPase activity is attributable to PfRuvB3 protein. The endogenous P. falciparum RuvB3 contains the characteristic ATPase and some DNA helicase activities. The confocal microscopy analysis showed that this protein is mainly expressed during intraerythrocytic schizont stages of the parasite and is localized to the nuclear region. Once merozoite comes out from schizont, PfRuvB3 protein distinctly relocalized to the subnuclear region. The co-localization studies with a nucleolar marker PfNop1 further suggest that in P. falciparum RuvB3 localizes into a discrete nuclear compartment. On the basis of these studies it can be speculated that P. falciparum RuvB3 is most likely required for intraerythrocytic schizogony., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Chromosome ends have been implicated in the default silencing of clonally variant gene families in the human malaria parasite Plasmodium falciparum. These chromosome regions are organized into heterochromatin, as defined by the presence of a repressive histone H3 lysine 9 trimethylated marker and heterochromatin protein 1. Here, we show that the non-coding subtelomeric region adjacent to virulence genes forms facultative heterochromatin in a cell cycle-dependent manner. We demonstrate that telomere-associated repeat elements (TAREs) and telomeres are transcribed as long non-coding RNAs (lncRNAs) during schizogony. Northern blot assays revealed two classes of lncRNAs: a ~4-kb transcript composed of telomere sequences and a TARE-3 element, and a >6-kb transcript composed of 21-bp repeats from TARE-6. These lncRNAs are transcribed by RNA polymerase II as single-stranded molecules. RNA-FISH analysis showed that these lncRNAs form several nuclear foci during the schizont stage, whereas in the ring stage, they are located in a single perinuclear compartment that does not co-localize with any known nuclear subcompartment. Furthermore, the TARE-6 lncRNA is predicted to form a stable and repetitive hairpin structure that is able to bind histones. Consequently, the characterization of the molecular interactions of these lncRNAs with nuclear proteins may reveal novel modes of gene regulation and nuclear function in P. falciparum., (Copyright © 2012 Elsevier B.V. All rights reserved.)