class i antigens , typified by the hla-abc antigens , are composed of a 43,000-molecular weight ( mw ) glycosylated transmembrane polypeptide with three external domains ( alpha 1 , alpha 2 and alpha 3 ) , of which the one nearest the membrane ( alpha 3 ) is associated with a 12,000-mw nonglycosylated polypeptide , beta 2-microglobulin .
C0019629
class i
C1519623
transmembrane