Yeast signal peptidase contains a glycoprotein and the Sec11 gene product

Partially purified yeast microsomal signal peptidase appears to be a complex of four polypeptides of 13, 18, 20, and 25 kDa. The 18-kDa chain is the product of the Sec11 gene, which is necessary for signal peptidase activity. The 25-kDa subunit is a glycoprotein that binds Con A. Two related methods for purification of the enzyme are presented; the first includes removal of peripheral membrane proteins from microsomes by alkali extraction, solubilization of the enzyme by nonionic detergent and high salt, and four different chromatographic procedures. An alternative method was developed based on lectin-affinity chromatography.