DNA-BINDING BY MADS-BOX TRANSCRIPTION FACTORS - A MOLECULAR MECHANISMFOR DIFFERENTIAL DNA BENDING

The serum response factor (SRF) and myocyte enhancer factor 2A (MEF2A) represent two human members of the MADS-box transcription factor fami ly. Each protein has a distinct biological function which is reflected by the distinct specificities of the proteins for coregulatory protei n partners and DNA-binding sites, In this study, we have investigated the mechanism of DNA binding utilized by these two related transcripti on factors. Although SRF and MEF2A belong to the same family and conta in related DNA-binding domains, their DNA-binding mechanisms differ in several key aspects, In contrast to the dramatic DNA bending induced by SRF, MEF2A induces minimal DNA distortion, A combination of loss- a nd gain-of-function mutagenesis identified a single amino acid residue located at the N terminus of the recognition helices as the critical mediator of this differential DNA bending. This residue is also involv ed in determining DNA-binding specificity, thus indicating a link betw een DNA bending and DNA-binding specificity determination. Furthermore , different basic residues within the putative recognition alpha-helic es are critical for DNA binding, and the role of the C-terminal extens ions to the MADS box in dimerization between SRF and MEF2A also differ s. These important differences in the molecular interactions of SRF an d MEF2A are likely to contribute to their differing roles in the regul ation of specific gene transcription.