Serum response factor (SRF) is a MADS transcription factor that binds to the CArG box sequence of the serum response element (SRE). Through its binding to CArG sequences, SRF activates several muscle-specific genes as well as genes that respond to mitogens. The thermodynamic parameters of the interaction of core-SRF (the 124–245 fragment of serum response fac-tor) with specific oligonucleotides from c-fos anddesminpromoters, were determined by spectroscopy.