DNA Chain Unwinding and Annealing Reactions of Lipocortin (Annexin) I Heterotetramer: Regulation by Ca2+ and Mg2+

Abstract Lipocortin I-S100 (calcyclin) heterotetramer exhibited ATPase activity in the presence of dsDNA but not ssDNA. To demonstrate its helicase activity, an 80-mer polynucleotide complementary to the replication origin of M13mp18 was synthesized, and the oligonucleotide, (dC) 20 , was ligated to either its 5′- or 3′- end for binding to lipocortin. Lipocortin I heterotetramer displaced chains of the partially Y-shaped duplexes with a dC-tail at either the 5′- or 3′- end. The chain displacement required ATP and Mg 2+ . Nonhydrolyzable ATP analogues were not effective. Lipocortin I heterotetramer also catalyzed annealing of the polynucleotides to M13mp18. Ca 2+ and phospholipids but not ATP and Mg 2+ were essential for this reaction. Since the chain displacing and annealing reactions were inhibited by monospecific anti-lipocortin I or anti-S100 antibodies, the present observations suggest that the lipocortin I heterotetramer regulates unwinding and annealing of DNA by Mg 2+ (plus ATP) and Ca 2+ (and phospholipids), respectively.