CONFORMATIONAL-CHANGES OF DNA MINICIRCLES UPON THE BINDING OF THE ARCHAEBACTERIAL HISTONE-LIKE PROTEIN MC1

Binding of the archaebacterial histone-like protein MC1 to DNA minicir cles has been examined by gel retardation and electron microscopy, MC1 preferentially binds to a 207-base pair relaxed DNA minicircle as com pared with the linear fragment. Random binding is observed at very low ionic strength, and a slight increase in salt concentration highly fa vors the formation of a complex that corresponds to the binding of two MC1 molecules per DNA ring. Measurements of dissociation rates show t hat this complex is remarkably stable, and electron microscopy reveals that it is characterized by two diametrically opposed kinks. These re sults are discussed in regard to the mechanisms by which MC1 affects D NA structure.