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Acta Crystallogr D Biol Crystallogr. 2003 Aug;59(Pt 8):1514-6. Epub 2003 Jul 23.

Crystallization and preliminary X-ray characterization of the relaxase domain of F factor TraI.

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Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.


Conjugative plasmids are capable of transferring a copy of themselves in single-stranded form from donor to recipient bacteria. Prior to transfer, one plasmid strand must be cleaved in a sequence-specific manner by a relaxase or mobilization protein. TraI is the relaxase for the conjugative plasmid F factor. A 36 kDa N-terminal fragment of TraI possesses the single-stranded DNA-binding and cleavage activity of the protein. Crystals of the 36 kDa TraI fragment in native and selenomethionine-labeled forms were grown by sitting-drop vapor-diffusion methods using PEG 1000 as the precipitant. Crystallization in the presence of chloride salts of magnesium and strontium was required to obtain crystals yielding high-resolution diffraction. To maintain high-resolution diffraction upon freezing, crystals had to be soaked in crystallization buffer with stepwise increases of ethylene glycol. The resulting crystals were trigonal and diffracted to a resolution of 3.1 A or better using synchrotron radiation.

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