Fig. 1. Composition of the Glc₃Man₉GlcNAc₂ oligosaccharide initially transferred to nascent glycoproteins. The outer box surrounds the monoglucosylated Glc₁Man₉GlcNAc₂ oligosaccharide recognized by calnexin and calreticulin. It is formed by the initial action of -glucosidase I followed by cleavage of a second glucose by -glucosidase II. The lectin sites of Cnx and Crt bind to the terminal glucose residue of the Glc₁Man₉GlcNAc₂ oligosaccharide as well as to three underlying mannose residues (dashed box). Also indicated is the terminal mannose residue cleaved by -mannosidase I to create a signal associated with rapid degradation of misfolded glycoproteins. Glc, glucose; Man, mannose; GlcNAc, N-acetylglucosamine.