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Glycophorin A

Glycophorin A (MNS blood group), also known as GYPA, is a protein which in humans is encoded by the GYPA gene. GYPA has also recently been designated CD235a (cluster of differentiation 235a).

Glycophorins A (GYPA; this protein) and B (GYPB) are major sialoglycoproteins of the human erythrocyte membrane which bear the antigenic determinants for the MN and Ss blood groups. In addition to the M or N and S or s antigens, that commonly occur in all populations, about 40 related variant phenotypes have been identified. These variants include all the variants of the Miltenberger complex and several isoforms of Sta; also, Dantu, Sat, He, Mg, and deletion variants Ena, S-s-U- and Mk. Most of the variants are the result of gene recombinations between GYPA and GYPB.

GypA, GypB and GypE are members of the same family and are located on the long arm of chromosome 4 (chromosome 4q31). The family evolved via two separate gene duplication events. The initial duplication gave rise to two genes one of subsequently evolved into GypA and the other which give rise via a second duplication event to GypB and GypE. These events appear to have occurred within a relatively short time span. The second duplication appears to have occurred via an unequal crossing over event.

The GypA gene itself consists of 7 exons and has 97% sequence homology with GypB and GypE from the 5' untranslated transcription region (UTR) to the coding sequence encoding the first 45 amino acids. The exon at this point encodes the transmembrane domain. Within the intron downstream of this pint is an Alu repeat. The cross over event which created the genes ancestral to GypA and GypB/E occurred within this region.

GypA can be found in all primates. GypB can be found only in gorillas and some of the higher primates suggesting that the duplication events occurred only recently.

There are about one million copies of this protein per erythrocyte.

The MNS blood group was the second set of antigens discovered. M and N were identified in 1927 by Landsteiner and Levine. S and s in were described later in 1947.

The frequencies of these antigens are

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protein-coding gene in the species Homo sapiens
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