Possible adhesion molecule with a role in early hematopoiesis by mediating the attachment of stem cells to the bone marrow extracellular matrix or directly to stromal cells. Could act as a scaffold for the attachment of lineage specific glycans, allowing stem cells to bind to lectins expressed by stromal cells or other marrow components. Presents carbohydrate ligands to selectins (By similarity). Selectively expressed on hematopoietic progenitor cells and vascular endothelium. On early hematopoietic progenitor cells. Highly glycosylated. Phosphorylated on serine residues by PKC. Belongs to the CD34 family.