Antisense Approaches to the Function of

SlOO refers to a protein fraction originally isolated from bovine brain over 25 years ago1 and termed SlOO to denote its partial solubility in 100 % saturated ammonium sulfate. The bovine brain SlOO fraction is composed primarily of two small (M, = lO,OOO), acidic, calcium binding proteins called SlOOa and These proteins share approximately 50 % identity in amino acid sequence and can form homologous and heterologous dirners of the form aa (SlOOa,), aP (SlOOa), and pp (S100b). The SlOOa and Sloop polypeptides are also characterized by the presence of regions of amino acid sequence that could form calcium binding structures: a conventional helix-loop-helix (EF-hand) calcium binding site in their COOH-terminal region and an NH2-terminal calcium binding site that resembles the site found in ~a lb ind in. ~. ~ SlOOa and Sloop are structurally conserved in different species. For example, the amino acid sequences of bovine, rat, and human Sloop differ by only 3-4 residues (see ref. 5). Less information is available about the structural conservation of the S100a polypeptide, but the bovine and rat proteins show only four amino acid differences (see ref. 6)