Transcriptional activity of serum response factor (SRF) is dependent oil its binding to the CC(A/T)(6)GG box (CArG box) of serum response element (SRE) By Raman spectroscopy, we carried out a comparative analysis. in solution, of the complexes obtained from the association of core-SRF with 20-mer SREs bearing wild-type and mutated c-fos CArG boxes. In case of association with the wild type c-fos CArG box, the complex does not Wing out the expected Raman signature of a stable bending of the targeted SRE but keeps a bend-linear conformer oligonucleotide interconversion The linear conformer Population is larger than that of free oligonucleotide In the core-SRF moiety of the wild-type complex a large spectral change associated with the CO-groups from Asp and/or Glu residues shows that their ionization states and the strength of their interactions decrease as compared to those of mutated non-specific complexes structural constraints evidenced on the free core-SRF are released in the wild-type complex and environmental heterogeneities appear in the vicinity of Tyr residues, Clue to higher water molecule access The H-bonding configuration of one Tyr OH-group, in average, changes with a net transfer from H-bond acceptor character to a combined donor and acceptor character A charge repartition distributed oil both core-SRF and targeted SRE stabilizes the specific complex, allowing the two partners to experience a variety of conformations. (c) 2009 Elsevier Inc All rights reserved.