Fig. 1. Protein structures, genomic organization and splicing of the CD34 family. (A) Schematic of protein structures. CD34, podocalyxin and endoglycan each have an extensively O-glycosylated (horizontal lines) and sialylated (horizontal lines with arrowheads) serine-, threonine- and proline-rich extracellular mucin domain (green), putative sites of N-glycosylation (lines with circles), a cysteine-containing globular domain (dark blue) and a juxtamembrane stalk region (yellow). Their single-pass transmembrane domains (light blue) are followed by short cytoplasmic tails (red) containing putative phosphorylation sites and C-terminal PDZ-domain docking sites (DTEL or DTHL). The extracellular unpaired cysteine residue of endoglycan can facilitate homodimerization; endoglycan also contains an unusual polyglutamic-acid-rich extracellular domain (pink box). (B) Genomic organizations. Each protein is encoded by eight exons, with individual exons encoding the corresponding domain in each protein. (C) Alternative splicing. CD34 and podocalyxin display identical patterns of alternative splicing, and can exist as truncated versions that lack most of the cytoplasmic tail.