Interaction with free beta ' subunit unmasks DNA-binding domain of RNA polymerase sigma subunit

The promoter recognition site on the sigma(70) initiation factor is shielde d from interaction with DNA unless sigma(70) is bound to the core component of RNA polymerase (RNAP). It is shown that interaction of sigma(70) With t he isolated beta' subunit of Escherichia coli RNAP is sufficient to induce unshielding of the DNA binding site. Using UV-induced DNA-protein cross-lin king we demonstrate that free beta' stimulates specific cross-links between region 2 of the sigma(70) polypeptide and a fragment of the non-template p romoter strand containing the TATAAT sequence. Thus the sigma beta' subasse mbly of RNAP can assume a functionally competent conformation independently of the bulk of the RNAP core, (C) 1999 Federation of European Biochemical Societies.