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 relativ 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 P3₁21 with unit cell dimensions of a = b = 35.0 Å and c = 141.2 Å. Diffraction data up to 2.6 Å 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.