Structure of the Escherichia coli RNA polymerase α subunit C-terminal domain

The alpha subunit C-terminal domain (alpha CTD) of RNA polymerase (RNAP) is a key element in transcription activation in Escherichia coli, possessing determinants responsible for the interaction of RNAP with DNA and with transcription factors. Here, the crystal structure of E. coli alpha CTD (alpha subunit residues 245-329) determined to 2.0 angstrom resolution is reported. Crystals were obtained after reductive methylation of the recombinantly expressed domain. The crystals belonged to space group P2(1) and possessed both pseudo-translational symmetry and pseudo-merohedral twinning. The refined coordinate model (R factor = 0.193, R-free = 0.236) has improved geometry compared with prior lower resolution determinations of the alpha CTD structure [Jeon et al. (1995), Science, 270, 1495-1497; Benoff et al. (2002), Science, 297, 1562-1566]. An extensive dimerization interface formed primarily by N-and C-terminal residues is also observed. The new coordinates will facilitate the improved modeling of alpha CTD-containing multi-component complexes visualized at lower resolution using X-ray crystallography and electron-microscopy reconstruction.