BASIC AND ACIDIC REGIONS FLANKING THE HMG DOMAIN OF MAIZE HMGA MODULATE THE INTERACTIONS WITH DNA AND THE SELF-ASSOCIATION OF THE PROTEIN

The maize HMGa protein is a typical member of the family of plant chro mosomal HMG1-like proteins. The HMG domain of HMGa is flanked by a bas ic N-terminal domain characteristic for plant HMG1-like proteins, and is linked to the acidic C-terminal domain by a short basic region. Var ious derivatives of the HMGa protein were expressed in Escherichia col i and purified. The individual HMG domain can functionally complement the defect of the HLT-like chromatin-associated Hbsu protein in Bacill us subtilis. The basic N-terminal domain which contacts DNA enhances t he affinity of the protein for linear DNA, whereas it has little effec t on the structure-specific binding to DNA minicircles. The acidic C-t erminal domain reduces the affinity of HMGa for linear DNA, but does n ot affect to the same extent the recognition of DNA structure which is an intrinsic property of the HMG domain. The efficiency of the HMGa c onstructs to facilitate circularization of short DNA fragments in the presence of DNA ligase is like the binding to linear DNA altered by th e basic and acidic domains flanking the HMG domain, while the supercoo ling activity of HMGa is only slightly influenced by the same regions, Both the basic N-terminal and thf: acidic C-terminal domains contribu te directly to the self-association of HMGa in the presence of DNA. Co llectively, these findings suggest that the intrinsic properties of th e HMG domain can be modulated within the HMGa protein by the basic and acidic domains.