Apolipoprotein B: The Ag(a1/d) Immunogenetic Polymorphism Coincides with a T‐to‐C Substitution at Nucleotide 1981, Creating an Alu I Restriction Site

Short cDNA fragments covering the entire coding region for apolipoprotein (apo) B have been cloned In the pING expression vector. A monoclonal antibody specific for the Ag(d) epltope on apo B has been used, together with the expressed apo B peptldes, to locate this epltope to a stretch of 26 amlno acids. Sequencing of this region from several genomlc DNAs of known Ag(a1/d) genotype showed a single T-to- C substitution at nucleotide 1981, creating an Alu I restriction site and resulting In a val to ala residue change In the corresponding peptlde (at position 591 In the mature protein). Southern blots, using the Alu I restriction endonuclease and a short probe for this region of the cDNA, showed perfect correspondence between the restriction fragment length polymorphism and the Ag(a1/d) Immunochemlcal polymorphism In all 17 persons examined.