Crystallization and structure analysis of Thermus flavus 5S rRNA helix B

The crystallization conditions of the synthetic RNA duplex r(GCGGCGU)*r(GCGCCGC), part of the Thermus flavus 5S rRNA domain B, were investigated in detail. The crystallization analysis revealed a relative narrow crystallization zone. Single sequence variations did not enhance the crystal quality, however the crystallization under microgravity provided crystals of higher quality. They belong to the space group P3(1)21 with unit cell dimensions of a = b = 35.0 A and c = 141.2 A. Diffraction data up to 2.6 A were collected and the structure subsequently analysed and refined to an R-value of 22.4 %. The conformation of the two molecules in the asymmetric unit is stabilized by intermolecular hydrogen bonds. The two molecules A and B are perpendicular to each other and interacting head to tail with symmetry related molecules. They form pseudo-continuous infinite helices in the crystal lattice.