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DNA bending in the ternary nucleoprotein complex at the c-fos promoter
1Department of Biochemistry and Genetics, Medical School, University of Newcastle upon Tyne, UK.
Abstract:
Transcriptional induction of the c-fos proto-oncogene in response to serum growth factors is mediated in part by a ternary complex that forms on the serum response element (SRE) within its promoter. This complex 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-induced DNA bending which occurs during the formation and post-translational modification of the ternary complex that forms at the c-fos SRE. Circular permutation analysis demonstrates that the minimal DNA-binding domain of SRF, which contains the MADS box, is sufficient to induce flexibility into the centre of its binding site within the SRE. Phasing analysis indicates that at least part of this flexibility results in the production of a directional bend towards the minor groove. The isolated 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 flexibility of the SRE. Phosphorylation of Elk-1 by MAP kinase (p42/ERK2) induces further minor changes in this DNA flexibility. However, phasing analysis reveals that the recruitment of Elk-1 to form the ternary complex affects the SRF-induced directional DNA bend in the SRE. The potential roles of DNA bending at the c-fos SRE are discussed.
Insights
Serum response factor (SRF) binding to the c-fos promoter induces DNA bending. Elk-1 recruitment and MAP kinase phosphorylation further modify this DNA flexibility and bending, impacting c-fos gene transcription.
Area of Science:
- Molecular Biology
- Gene Regulation
- Protein-DNA Interactions
Background:
- The c-fos proto-oncogene's transcriptional induction by serum growth factors involves a ternary complex at the serum response element (SRE).
- This complex comprises Elk-1, serum response factor (SRF), and the SRE, with Elk-1 phosphorylation by MAP kinase correlating with c-fos induction.
Purpose of the Study:
- To investigate protein-induced DNA bending during the formation and post-translational modification of the ternary complex at the c-fos SRE.
- To understand how SRF and Elk-1 binding, along with Elk-1 phosphorylation, influence DNA structure at the c-fos promoter.
Main Methods:
- Circular permutation analysis to assess DNA bending induced by SRF.
- Phasing analysis to determine the directionality and nature of DNA bending.
- Investigated DNA bending changes upon Elk-1 binding and Elk-1 phosphorylation by MAP kinase (p42/ERK2).
Main Results:
- The minimal DNA-binding domain of SRF (MADS box) is sufficient to induce flexibility and a directional bend towards the minor groove at the SRE.
- Isolated ETS domains of Elk-1 and SAP-1 did not induce DNA bending.
- Ternary complex formation with Elk-1 altered SRE flexibility, and Elk-1 phosphorylation caused minor flexibility changes.
- Elk-1 recruitment modulated the SRF-induced directional DNA bend at the SRE.
Conclusions:
- SRF binding induces significant DNA bending at the c-fos SRE, which is further modulated by Elk-1 binding and phosphorylation.
- These structural changes in DNA flexibility and bending likely play roles in regulating c-fos transcription initiation.