ESCHERICHIA-COLI-SIGMA-70 AND NUSA PROTEINS .2. PHYSICAL-PROPERTIES AND SELF-ASSOCIATION STATES

In this paper we examine the physical properties and potential for self-association of the Escherichia coli transcription factors, σ70 and NusA. We show, by a combination of chemical crosslinking, equilibrium and velocity sedimentation, quasi-elastic light scattering, and small-angle X-ray scattering that NusA exists as a monomer at KCl concentrations between 0.01 and 1.5m, and that σ70 exists as a monomer at KCl concentrations between 0.1 and 1.5m. The shape and hydration characteristics of each of these monomeric proteins are also examined. The results serve as background for the companion paper in which a thermodynamic analysis is made of the interactions of these transcription factors with E. coli core RNA polymerase in solution and as a component of the functional transcription complex. © 1991.