Escherichia coli RNA polymerase subunit omega and its N-terminal domain bind full-length beta ' to facilitate incorporation into the alpha(2)beta subassembly

The omega subunit of Escherichia coli RNA polymerase, consisting of 90 amin o acids, is present in stoichiometric amounts per molecule of core RNA poly merase (alpha (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 th e maturation of RNA polymerase. The X-ray structure of Thermus aquaticus co re RNA polymerase suggests that two regions of omega latch on to beta' at i ts 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 doma in, implying that omega binding requires both these regions of beta'. We fu rther show that omega can prevent the aggregation of beta' during its renat uration in vitro and that a V8-protease-resistant 52-amino-acid-long N-term inal domain of omega is sufficient for binding and renaturation of beta'. C D and functional assays show that this N-terminal fragment retains the stru cture of native omega and is able to enhance the reconstitution of core RNA polymerase. Reconstitution of core RNA polymerase from its individual subu nits proceeds according to the steps alpha + alpha --> alpha (2) + beta --> alpha (2)beta + beta' --> alpha (2)beta beta'. It is shown here that w par ticipates during the last stage of enzyme assembly when beta' associates wi th the alpha (2)beta subassembly.