Full Length Research Paper

Assessing the role of RecA protein in the radioresistant bacterium, Deinococcus geothermalis

Haïtham Sghaier¹*, Katsuya Satoh^{2, 3}, Hirofumi Ohba^{2, 3} and Issay Narumi^{2, 3}

¹Research Unit UR04CNSTN01 "Medical and Agricultural Applications of Nuclear Techniques", National Center for Nuclear Sciences and Technology (CNSTN), Sidi Thabet Technopark, 2020 Sidi Thabet, Tunisia.

²DNA Repair Protein Group, Research Unit for Quantum Beam Life Science Initiative, Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.

³Gene Resource Research Group, Radiation-Applied Biology Division, Quantum Beam Science Directorate, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.

*Corresponding author. E-mail: sghaier.haitham@gmail.com, haitham.sghaier@cnstn.rnrt.tn. Tel: +216-71-537-410. Fax: +216-71-537-555.

Accepted 19 February, 2010.

   Abstract

The moderately thermophilic bacterium Deinococcus geothermalis exhibits extraordinary resistance to ionizing radiation. RecA protein is considered to be one of the most important participants in radioresistance. To assess the role of the RecA protein in D. geothermalis, the recA gene was isolated from D. geothermalis and over expressed in Escherichia coli. After the D. geothermalis RecA protein (GeoRecA) was purified, the recombination activity was investigated in vitro. GeoRecA efficiently promoted the strand exchange reaction between homologous linear double-stranded DNA and circular single-stranded DNA substrates at 50°C. Like Deinococcus radiodurans RecA protein (DraRecA), GeoRecA could promote DNA strand exchange reaction through normal and inverse pathways. Furthermore, GeoRecA complemented the RecA deficiency of D. radiodurans. These results indicate that GeoRecA is a functional homologue of DraRecA and plays an important role in radioresistance. However, unlike DraRecA, GeoRecA could not complement the RecA deficiency of E. coli, suggesting that GeoRecA require more strict intracellular conditions than DraRecA does to fulfill its function. This study provides new insights into the role of deinococcal RecA protein in radioresistance.

Key words: Deinococcus geothermalis, DNA repair, DNA strand exchange, radio resistance, RecA.