cDNA cloning of human apoA-I: amino acid sequence of preproapoA-I.

ds-cDNA to human liver apoA-I mRNA has been cloned. Nucleic acid sequence analysis revealed that apoA-I mRNA codes for a precursor apolipoprotein, preproapoA-I, which contains 24 amino acids on the NH2-terminal end of the mature plasma apoA-I. Eighteen amino acids are contained within the hydrophobic prepeptide (Met-Lys-Ala-Ala-Val-Leu-Thr-Leu-Ala-Val-Leu-Phe-Leu-Thr-Gly-Ser-Gln-Ala) followed by a 6 amino acid propeptide (Arg-His-Phe-Trp-Gln-Gln). Our results on human apoA-I are in agreement with the partial sequence of the precursor of rat apoA-I with respect to the length of the precursor sequence, location of the prepeptide, and the presence of an unusual propeptide sequence terminating in a neutral dipeptide Gln-Gln. A detailed analysis of the primary structure of normal human apoA-I mRNA will be essential to our ultimate understanding of the processing of human apoA-I and diseases characterized by molecular defects in apoA-I structure and function.