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

Highly purified Escherichia coli RNA polymerase contains a small subunit te rmed omega that has a molecular mass of 10 105 Da and is comprised of 91 am ino acids. E. coli strains lacking omega (omega-less) are viable, but exhib it a slow-growth phenotype. Renaturation of RNA polymerase isolated from an omega-less mutant, in the presence of omega, resulted in maximum recovery of activity. The omega-less RNA polymerase from omega-less strains recruits the chaperonin, GroEL (unlike the wild-type enzyme), suggesting a structur al deformity of the mutant enzyme. The GroEL-containing core RNA polymerase interacts efficiently with sigma(70) to generate the fully functional holo enzyme. However, when GroEL was removed, the enzyme was irreversibly nonfun ctional and was unable to bind to sigma(70). The damaged enzyme regained ac tivity after going through a cycle of denaturation and reconstitution in th e presence of omega or GroEL. GroES was found to have an inhibitory effect on the core-sigma(70) association unlike the w subunit. The omega subunit m ay therefore be needed for stabilization of the structure of RNA polymerase .