Lipocortin (Annexin) I heterotetramer binds to purine RNA and pyrimidine DNA

Lipocortin I-like protein with a molecular weight of 94,000 Da as judged by Western analysis was found to bind to ssDNA rather than to dsDNA in a Ca2+-dependent manner. This protein was also bound to [P-32]poly(rA) and [P-32]poly(rG) as measured by EMSA. Poly(rG;), poly(rA), poly(dC), and poly(dT) were competitive against binding of either [P-32]poly(rA) or [P-32]poly(rG), while poly(rC), poly(rU), and poly(dA) were less effective binding competitors. The binding of this protein to poly(rA) or poly(rG) was inhibited by immunoprecipitable anti-lipocortin I (calpactin II) and anti-S100 protein antibodies, but not by an anti-Ig antibody. Phospholipids such as phosphatidylserine and phosphatidylinositol enhanced the binding of lipocortin I to poly(rA). Taken together, our present observations suggest that the lipocortin I-S100 protein heterotetramer binds to either purine RNAs or pyrimidine ssDNAs in a Ca2+- and phospholipid-dependent manner. (C) 1999 Academic Press.