Wheat HMGa protein is a typical member of the plant HMGA family It has four AT hooks and a histone H1-like region Apanel of deletion mutants of HMGa was generated to study the role of different regions of HMGa in its binding to 4h (a synthetic DNA that mimics the in vivo structure of intermediated of homologus recombination and DNA repair) and linear DNAs Although the histone H1-like region of HMGs does not bind to 4H or linear DNAs it does enhance the binding Mutants with any two adjacent AT hooks show specific binding to both 4h and linear P268 (and P31) with different binding affinities which is partly due to the flaking regions between AT hooks Conformational studies indicatie that the alpha-helical content of HMGa increases singificantly when it binds to 4J compared to that after binding to p31 Linera DNA In contrast linear DNA but not 4H undeoges substantial conformational change when it binds ot HMGa indication that linear DNA is relatively more flexible than 4H A more significat difference in hte affinities of binding of the mutants of HMGs to 4H was observed compared to their affinities of binding to linear DNA p31 These differences could be due to the rigidity of hte dna and the characters of the AT hook regions in the mutants.
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