THE NUMBER OF KRINGLE IV REPEATS 3-10 IS INVARIABLE IN THE HUMAN APO(A) GENE

Abstract The human apolipoprotein(a) ( apo(a) ) gene is a member of a family of related genes including plasminogen , apo(a)rg-B and apo(a)rg-C , which are clustered on chromosome 6q 2,7. Apo(a) contains ten different types of plasminogen-like kringle IV repeats (K-IV 1–10) one of which (K-IV 2) varies in number resulting in a remarkable size polymorphism of the protein. Sequence analysis of human apo(a) alleles and indirect evidence have suggested that K-IV 1 and K-IV 3–10 are each present once in individual alleles and that the 3′ apo(a) region encompassing kringles IV 3–10, kringle V and the protease domain is invariable. To directly test this, we have constructed a restriction map of the apo(a) gene region from genomic DNA and from a yeast artificial chromosome (YAC) (K-IV 13) which contains the entire apo(a) gene. The presence of a 63 kb Cla I fragment encompassing kringles IV 3–10, kringle V and the protease domain and a 46 kb Swa I fragment, spanning kringles IV 5–10, kringle V and the protease domain was demonstrated by PFGE/Southern blotting in 30 unrelated subjects, who represented a range of apo(a) size alleles containing from 11 to 49 kringles. Our analysis demonstrates that the number of kringles IV 3–10 is invariable in the human apo(a) gene, suggesting that the 3′ domain of Apo(a) is functionally important.