# Escherichia coli RNA polymerase subunit \omega and its n- terminal domain bind full-length \beta to facilitate incorporation into the ${\alpha}_{\mathrm{2}}$\beta subassembly

Ghosh, Pallavi and Ishihama, Akira and Chatterji, Dipankar (2001) Escherichia coli RNA polymerase subunit \omega and its n- terminal domain bind full-length \beta to facilitate incorporation into the ${\alpha}_{\mathrm{2}}$\beta subassembly. In: European Journal of Biochemistry, 268 (17). pp. 4621-4627.

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The v subunit of Escherichia coli RNA polymerase,consisting of 90 amino acids, is present in stoichiometric amounts per molecule of core RNA polymerase (${\alpha}_{\mathrm{2}}$\beta\beta'). The presence of \omega is necessary to restore denatured RNA polymerase in vitro to its fully functional form, and, in an \omega-less strain of E. coli, GroEL appears to substitute for \omega in the maturation of RNA polymerase. The X-ray structure of Thermus aquaticus core RNA polymerase suggests that two regions of \omega latch on to \beta' at its N-terminus and C-terminus. We show here that \omega binds only the intact \beta^' subunit and not the \beta' N-terminal domain or \beta' C-terminal domain, implying that \omega binding requires both these regions of \beta. We further show that \omega can prevent the aggregation of \beta' during its renaturation in vitro and that a V8-protease-resistant 52-amino-acidlong N-terminal domain of \omega is sufficient for binding and renaturation of \beta'. CD and functional assays show that this N-terminal fragment retains the structure of native \omega and is able to enhance the reconstitution of core RNA polymerase. Reconstitution of core RNA polymerase from its individual subunits proceeds according to the steps \alpha +\alpha \rightarrow \alpha2 + \beta \rightarrow ${\alpha}_{\mathrm{2}}$\beta +\beta' \rightarrow ${\alpha}_{\mathrm{2}}$\beta\beta'. It is shown here that \omega participates during the last stage of enzyme assembly when \beta' associates with the ${\alpha}_{\mathrm{2}}$\beta subassembly.