COMPLEMENTATION CLONING OF S2P, A GENE ENCODING A PUTATIVE METALLOPROTEASE REQUIRED FOR INTRAMEMBRANE CLEAVAGE OF SREBPS

We report the cloning of a gene, S2P, that encodes a putative metallop rotease required for intramembrane proteolysis of sterol-regulatory el ement-binding proteins (SREBPs) at Site-2, SREBPs are membrane-bound t ranscription factors that activate genes regulating cholesterol metabo lism. The active NH2-terminal domains of SREBPs are released from memb ranes by sequential cleavage at two sites: Site-1, within the lumen of the endoplasmic reticulum; and Site-5, within a transmembrane segment , The human S2P gene was cloned by complementation of mutant CHO cells that cannot cleave SREBPs at Site-2 and are cholesterol auxotrophs. S 2P defines a new family of polytopic membrane proteins that contain an HEXXH sequence characteristic of zinc metalloproteases, Mutation of t he putative zinc-binding residues abolishes S2P activity, S2P encodes an unusual metalloprotease that cleaves proteins within transmembrane segments.