Fig. 1. Mammalian glycan structures. Mammalian glycans discussed in the text are depicted using sugar symbols. (A) N-glycans; (B) mucin O-glycans; and (C) O-fucose glycans. The glycosyltransferase that initiates the transition shown is represented by its biochemical abbreviation and by its gene name (in parentheses). N-glycans (A) occur at NXS/T (where X is any amino acid) sequences, and O-glycans (B) at Ser or Thr (S/T). (C) O-FucT-1 transfers only to EGF (epidermal growth factor) repeats with a particular consensus sequence (Cys-Cys bonds, 1-6, are highlighted in yellow). A dashed line signifies that several reactions must occur before obtaining the product shown. A solid line designates a single reaction. Maternal and zygotic mutants of each glycosysyltransferase are discussed in the text. Fuc, fucose; Gal, galactose; Man, mannose; GalNAc, N-acetylgalactosamine; GlcNAc, N-acetylglucosamine. Image courtesy of Pamela Stanley.