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Article
Subject Categories: Structural Biology | Microbiology & Pathogens
The EMBO Journal (2005) 24, 270–282, doi:10.1038/sj.emboj.7600530
Published online 6 January 2005
Bacterial chromosome segregation: structure and DNA binding of the Soj dimer — a conserved biological switch
Thomas A Leonard, P Jonathan Butler and Jan Löwe
MRC Laboratory of Molecular Biology, Cambridge, UK

To whom correspondence should be addressed
Thomas A Leonard, MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK. Tel.: +44 1223 252 696; Fax: +44 1223 213 556; E-mail: tleonard@mrc-lmb.cam.ac.uk or jyl@mrc-lmb.cam.ac.uk

Received 14 September 2004; Accepted 29 November 2004; Published online 6 January 2005.
Abstract
Soj and Spo0J of the Gram-negative hyperthermophile Thermus thermophilus belong to the conserved ParAB family of bacterial proteins implicated in plasmid and chromosome partitioning. Spo0J binds to DNA near the replication origin and localises at the poles following initiation of replication. Soj oscillates in the nucleoid region in an ATP- and Spo0J-dependent fashion. Here, we show that Soj undergoes ATP-dependent dimerisation in solution and forms nucleoprotein filaments with DNA. Crystal structures of Soj in three nucleotide states demonstrate that the empty and ADP-bound states are monomeric, while a hydrolysis-deficient mutant, D44A, is capable of forming a nucleotide 'sandwich' dimer. Soj ATPase activity is stimulated by Spo0J or the N-terminal 20 amino-acid peptide of Spo0J. Our analysis shows that dimerisation and activation involving a peptide containing a Lys/Arg is conserved for Soj, ParA and MinD and their modulators Spo0J, ParB and MinE, respectively. By homology to the nitrogenase iron protein and the GTPases Ffh/FtsY, we suggest that Soj dimerisation and regulation represent a conserved biological switch.
Keywords: chromosome segregation, MinCD, ParAB, Soj, Spo0J
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