Effect of DNA binding protein Ssh12 from hyperthermophilic archaeon Sulfolobus shibatae on DNA supercoiling

An 11.5-ku DNA binding protein, designated as Ssh12, was purified from the hyperthermophilic archaeon Sulfolobus shibatae by column chromatography in SP Sepharose, DNA cellulose and phosphocellulose. Ssh12 accounts for about 4% of the total cellular protein. The protein is capable of binding to both negatively supercoiled and relaxed DNAs. Nick closure analysis revealed th at Ssh12 constrains negative supercoils upon binding to DNA. While the abil ity of the protein to constrain supercoils is weak at 22 degrees C, it is e nhanced substantially at temperatures higher than 37 degrees C. Both the ce llular content and supercoil-constraining ability of Ssh12 suggest that the protein may play an important role in the organization and stabilization o f the chromosome of S. shibatae.