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GTP-dependent polymerization of the tubulin-like RepX replication protein encoded by the pXO1 plasmid of Bacillus anthracis.

Department of Microbiology and Molecular Genetics, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
Molecular Microbiology (Impact Factor: 5.03). 03/2008; 67(4):881-90. DOI: 10.1111/j.1365-2958.2007.06100.x
Source: PubMed

ABSTRACT RepX protein encoded by the pXO1 plasmid of Bacillus anthracis is required for plasmid replication. RepX harbours the tubulin signature motif and contains limited amino acid sequence homology to the bacterial cell division protein FtsZ. Although replication proteins are not known to polymerize, here we show by electron microscopy that RepX undergoes GTP-dependent polymerization into long filaments. RepX filaments assembled in the presence of GTPgammaS were more stable than those assembled in the presence of GTP, suggesting a role for GTP hydrolysis in the depolymerization of the filaments. Light scattering studies showed that RepX underwent rapid polymerization, and substitution of GTP with GTPgammaS stabilized the filaments. RepX exhibited GTPase activity and a mutation in the tubulin signature motif severely impaired its GTPase activity and its polymerization in vitro. Unlike FtsZ homologues, RepX harbours a highly basic carboxyl-terminal region and exhibits GTP-dependent, non-specific DNA binding activity. We speculate that RepX may be involved in both the replication and segregation of the pXO1 plasmid.

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    • "Circles are opposite genomes containing whole pXO1 (red), pXO2 (fuchsia), or d-endotoxin genes (green) or were isolated on the same day from Rockville, Maryland (blue). We have also indicated genomes likely containing pXO1-like (brown) or pXO2- like (burgundy) plasmids based on the presence of the RepX (Anand et al. 2008) or RepS (Tinsley et al. 2004) proteins, respectively. Each genome has a bar graph showing the proportion of genes belonging to core (brown), character (ocher), and accessory (pink) classes. "
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