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J. Biol. Chem., Vol. 281, Issue 25, 16978-16984, June 23, 2006

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The Two Plasmodium falciparum Nucleosome Assembly Proteins Play Distinct Roles in Histone Transport and Chromatin Assembly^*

From the Structural and Computational Biology Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), New Delhi, India PIN-110067

The malarial parasite Plasmodium falciparum has two nucleosome assembly proteins, PfNapS and PfNapL (Chandra, B. R., Olivieri, A., Silvestrini, F., Alano, P., and Sharma, A. (2005) Mol. Biochem. Parasitol. 142, 237–247). We show that both PfNapS and PfNapL interact with histone oligomers but only PfNapS is able to deposit histones onto DNA. This property of PfNapS is divalent cation-dependent and ATP-independent. Deletion of the terminal subdomains of PfNapS abolishes its nucleosome assembly capabilities, but the truncated protein retains its ability to bind histones. Both PfNapS and PfNapL show binding to the linker histone H1 suggesting their probable role in extraction of H1 from chromatin fibers. Our data suggests distinct sites of interaction for H1 versus H3/H4 on PfNapS. We show that PfNapS and PfNapL are phosphorylated both in vivo and in vitro by casein kinase-II, and this modification is specifically inhibited by heparin. Circular dichroism, fluorescence spectroscopy, and chymotrypsin fingerprinting data together suggest that PfNapL may undergo very small and subtle structural changes upon phosphorylation. Specifically, phosphorylation of PfNapL increases its affinity 3-fold for core histones H3, H4, and for the linker histone H1. Finally, we demonstrate that PfNapS is able to extract histones from both phosphorylated and unphosphorylated PfNapL, potentially for histone deposition onto DNA. Based on these results, we suggest that the P. falciparum NapL is involved in the nucleocytoplasmic relay of histones, whereas PfNapS is likely to be an integral part of the chromatin assembly motors in the parasite nucleus.

Received for publication, March 9, 2006 , and in revised form, April 19, 2006.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental information.

¹ Both authors contributed equally to this work.

² Supported by CSIR, India, Senior Research Fellowships.

³ A Wellcome Trust International Senior Research Fellow. To whom correspondence should be addressed: Structural and Computational Biology Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg New Delhi, India, PIN-110067. Tel.: 9111-26711731; Fax: 9111-26711731; E-mail: asharma{at}icgeb.res.in.

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