DNA BENDING IN THE TERNARY NUCLEOPROTEIN COMPLEX AT THE C-FOS PROMOTER

Transcriptional induction of the c-fos proto-oncogene in response to s erum growth factors is mediated in part by a ternary complex that form s on the serum response element (SRE) within its promoter, This comple x consists of Elk-1, serum response factor (SRF) and the SRE, Elk-1 is phosphorylated by MAP kinase, which correlates with the induction of c-fos transcription, In this study we have investigated the protein-in duced DNA bending which occurs during the formation and post-translati onal modification of the ternary complex that forms at the c-fos SRE, Circular permutation analysis demonstrates that the minimal DNA-bindin g domain of SRF, which contains the MADS box, is sufficient to induce flexibility into the centre of its binding site within the SRE, Phasin g analysis indicates that at least part of this flexibility results in the production of a directional bend towards the minor groove, The is olated ETS domains from Elk-1 and SAP-1 induce neither DNA bending nor increased DNA flexibility, Formation of ternary complexes by binding of Elk-1 to the binary SRF:SRE complex results in a change in the flex ibility of the SRE, Phosphorylation of Elk-1 by MAP kinase (p42/ERK2) induces further minor changes in this DNA flexibility, However, phasin g analysis reveals that the recruitment of Elk-1 to form the ternary c omplex affects the SRF-induced directional DNA bend in the SRE. The po tential roles of DNA bending at the c-fos SRE are discussed.