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Nucleic Acids Research Advance Access published online on July 28, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn483
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© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Molecular Biology

DNA organization by the apicoplast-targeted bacterial histone-like protein of Plasmodium falciparum

E. V. S. Raghu Ram1, Rangeetha Naik2, Munia Ganguli2 and Saman Habib1,*

1Division of Molecular and Structural Biology, Central Drug Research Institute, Lucknow-226 001 and 2Institute of Genomics and Integrative Biology, Delhi-110 007, India

*To whom correspondence should be addressed. Tel: +91 522 2612411 to 418, ext. 4282; Fax: +91 522 2623405/2623938/2629504; Email: saman.habib{at}gmail.com; samamit{at}lycos.com

Received March 4, 2008. Revised July 10, 2008. Accepted July 11, 2008.

Apicomplexans, including the pathogens Plasmodium and Toxoplasma, carry a nonphotosynthetic plastid of secondary endosymbiotic origin called the apicoplast. The P. falciparum apicoplast contains a 35 kb, circular DNA genome with limited coding capacity that lacks genes encoding proteins for DNA organization and replication. We report identification of a nuclear-encoded bacterial histone-like protein (PfHU) involved in DNA compaction in the apicoplast. PfHU is associated with apicoplast DNA and is expressed throughout the parasite's intra-erythocytic cycle. The protein binds DNA in a sequence nonspecific manner with a minimum binding site length of ~27 bp and a Kd of ~63 nM and displays a preference for supercoiled DNA. PfHU is capable of condensing Escherichia coli nucleoids in vivo indicating its role in DNA compaction. The unique 42 aa C-terminal extension of PfHU influences its DNA condensation properties. In contrast to bacterial HUs that bend DNA, PfHU promotes concatenation of linear DNA and inhibits DNA circularization. Atomic Force Microscopic study of PfHU–DNA complexes shows protein concentration-dependent DNA stiffening, intermolecular bundling and formation of DNA bridges followed by assembly of condensed DNA networks. Our results provide the first functional characterization of an apicomplexan HU protein and provide additional evidence for red algal ancestry of the apicoplast.


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