The Colton blood group system consists of four antigens carried on a multipass membrane glycoprotein called aquaporin 1 (AQP1; aka Channel-forming integral protein). It consists of 269 amino acids and both amino and carboxyl termini are predicted to be intracellular. The LRG_808 (NG_007475.2) includes more than one gene; the AQP1 gene encoding for the CO blood group antigens is located in the range 63301 to 77124.
Reference allele CO*01.01 encodes: CO1, CO3, CO4
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