Purification, crystallization and initial crystallographic analysis of RNA polymerase holoenzyme from Thermus thermophilus

RNA polymerase holoenzyme from Thermus thermophilus, consisting of six protein subunits (alpha(2), beta, beta', omega and sigma(70)) and having a total molecular mass of about 450 kDa, was purified and crystallized by the hanging-drop vapour-diffusion technique under mild near-physiological conditions. The crystals diffract beyond 3 Angstrom resolution. Careful analysis of diffraction data revealed that the crystals belong to space group P3(2), with unit-cell parameters a = b = 236.35, c = 249.04 Angstrom, and have perfect twinning along the threefold axis. A complete data set at 3 Angstrom resolution was collected and an unambiguous molecular-replacement solution was found using the structure of T. aquaticus RNA polymerase core enzyme as a search model. The refinement of structure and model building of the sigma(70) subunit is now in progress.