FORMATION OF A DENATURED DIMER LIMITS THE THERMAL-STABILITY OF ARC REPRESSOR

The thermal stability of the Arc repressor dimer normally increases wi th concentration because protein folding and subunit association are t hermodynamically coupled. At Arc concentrations above 100 mu M, howeve r, thermal denaturation remains reversible and cooperative but t(m) do es not continue to increase. In this concentration regime, thermally d enatured Arc shows significantly reduced secondary structure and no ev idence of a tightly packed core, but light scattering and fluorescence polarization studies indicate that the protein is dimeric. Higher ord er denatured oligomers are not observed and the stability of the non-n ative dimer is reduced by Arc mutations, indicating that non-native di merization involves specific interactions between Arc subunits. (C) 19 97 Academic Press Limited.