GroEL is involved in activation of Escherichia coli RNA polymerase devoid of the σ subunit in vivo

Abstract

Highly purified Escherichia coli RNA polymerase contains a small subunit termed ω that has a molecular mass of 10 105 Da and is comprised of 91 amino acids. E. coli strains lacking ω (ω-less) are viable, but exhibit a slow-growth phenotype. Renaturation of RNA polymerase isolated from an ω-less mutant, in the presence of ω, resulted in maximum recovery of activity. The ω-less RNA polymerase from ω-less strains recruits the chaperonin, GroEL (unlike the wild-type enzyme), suggesting a structural deformity of the mutant enzyme. The GroEL-containing core RNA polymerase interacts efficiently with σ⁷⁰ to generate the fully functional holoenzyme. However, when GroEL was removed, the enzyme was irreversibly nonfunctional and was unable to bind to σ⁷⁰. The damaged enzyme regained activity after going through a cycle of denaturation and reconstitution in the presence of ω or GroEL. GroES was found to have an inhibitory effect on the core-σ⁷⁰ association unlike the ω subunit. The ω subunit may therefore be needed for stabilization of the structure of RNA polymerase.