SPATIAL ARRANGEMENT OF SIGMA-FACTOR AND CORE ENZYME OF ESCHERICHIA-COLI RNA-POLYMERASE - A NEUTRON SOLUTION SCATTERING STUDY

By means of neutron solution scattering we determined the position and orientation of core enzyme and σ-factor within the Escherichia coli RNA polymerase holoenzyme with the aim of improving existing models. The individual components, core enzyme (E) and σ-factor (σ), were highlighted by deuterium labeling and their center-to-center distances determined in the monomeric and the dimeric holoenzyme. The following distance parameters were obtained: dE = 8.6(± 1) nm, dE = 11.5(± 1) nm, dσ = 12.0(±0.7) nm, dE = 9(± 3) nm. Using a triangulation procedure the position of the σ-factors, σ1 and σ2, were determined with respect to the mass center of the core enzyme molecules, E1 and E2 assuming a symmetrical arrangement of the holoenzyme molecules in the dimer (C2 symmetry). In addition, the orientation of the σ-factor with respect to core enzyme was estimated by means of model calculations. The obtained model of holoenzyme depicts the σ-factor as buried in a groove of core enzyme, probably between the large subunits β′ and β. © 1991.