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

The α subunit C-terminal domain (αCTD) 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 αCTD (α subunit residues 245–329) determined to 2.0 Å resolution is reported. Crystals were obtained after reductive methylation of the recombinantly expressed domain. The crystals belonged to space group P2₁ 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 αCTD 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 αCTD-containing multi-component complexes visualized at lower resolution using X-ray crystallo­graphy and electron-microscopy reconstruction.