['DNA supercoiling factor (SCF) was first identified in the silkworm as a protein capable of generating negative supercoils into a relaxed DNA in conjunction with eukaryotic topoisomerase II. Drosophila melanogaster SCF localizes to puffs on polytene chromosomes, implicating its role in gene expression. The factor is a Ca2+-binding protein with four EF-hand domains and possesses a tetrapeptide sequence HDEF at its C-terminus.', 'To clarify the roles of the domains of SCF, we carried out a functional dissection of the factor. A glutamic acid to glutamine substitution at the end of the loop in EF-hand domain II or III reduced both the Ca2+ binding and supercoiling activities; simultaneous substitutions at both sites abolished these activities. During native polyacrylamide gel electrophoresis, SCF migrated more rapidly in the presence of Ca2+ than in the presence of Mg2+ or EGTA. SCF binds directly to topoisomerase II. Deletion of the C-terminal HDEF sequence destroyed the binding and supercoiling activity.'] Are functional dissection of DNA supercoiling factor : EF-hand domains and C-terminal HDEF motif essential for its activity?