Analysis of cDNA clones encoding the entire B-26 region of human apolipoprotein B.

We report the characterization of intestine and liver cDNA clones for human apolipoprotein B (apoB) that map to the 5' end of the mRNA. The protein sequence encoded by the 5011 nucleotides derived from sequence analysis of these clones includes 1643 amino acid residues of the mature protein of Mr 184,000. The amino acid sequence at the amino terminus of B-74 peptide was determined and mapped to residue 1298. The size (Mr 145,700) and amino acid composition of the B-26 region encoded by these clones (including amino acid residues 1-1297) closely match the values obtained from the B-26 peptide. The amino acid sequence of peptide B-100 at the junction of peptides B-26 and B-74 (Phe-Lys decreases- Ser) shows structural homology to the site on human kininogen (Phe-Arg decreases- Ser) that is cleaved by the protease plasma kallikrein. The encoded protein contains five potential N-glycosylation sites and several regions in which the hydroxyamino acids, serine and threonine, are present in high abundance. The protein sequence presented in this report represents approximately 30% of the total B-100 protein and will aid in the characterization of additional cDNA clones.