Crystal structures of the chromosomal proteins Sso7d/Sac7d bound to DNA containing T-G mismatched base-pairs

Sso7d and Sac7d are two small chromatin proteins from the hyperthermophilic archaeabacterium Sulfolobus solfataricus and Sulfolobus acidocaldarius, re spectively. The crystal structures of Sso7d-GTGATCGC, Sac7d-GTGATCGC and Sa c7d-GTGATCAC have been determined and refined at 1.45 Angstrom, 2.2 Angstro m and 2.2 Angstrom, respectively, to investigate the DNA binding property o f Sso7d/Sac7d in the presence of a T-G mismatch base-pair. Detailed structu ral analysis revealed that the intercalation site includes the T-G mismatch base-pair and Sso7d/Sac7d bind to that mismatch base-pair in a manner simi lar to regular DNA. Ln the Sso7d-GTGATCGC complex, a new inter-strand hydro gen bond between T204 and C14N4 is formed and well-order bridging water mol ecules are found. The results suggest that the less stable DNA stacking sit e involving a T-G mismatch may be a preferred site for protein side-chain i ntercalation. (C) 2000 Academic Press.