Isolation, characterization, and mapping to chromosome 19 of the human apolipoprotein E gene.

The human apo-E gene has been isolated from a X phage library using as a probe the previously reported apo-E cDNA clone pE-301.X apo-E was mapped and subcloned, and the apo-E gene was completely sequenced.The DNA sequence was compared with that of a near full length cDNA clone pE-368 and revealed three introns.The first intron was in the region that corresponds to the 5' untranslated region of apo-E mRNA.The second intron interrupted the codon specifying amino acid -4 of the apo-E signal peptide.The third intron interrupted the codon specifying amino acid 61 of the mature protein.Analysis of the DNA sequence revealed four Alu sequences.Two were in opposite orientations in the second intron, and one each occurred in the regions 5' and 3' to the apo-E gene.There were two base differences between the apo-E gene sequence and the sequence derived from the cDNA clones.At the codon for amino acid residue 112, the apo-E gene contained CGC, specifying Arg, whereas the cDNA contained TGC, specifying Cys.The other base difference was in the area corresponding to the 5' untranslated region of apo-E mRNA.Apo-E is commonly polymorphic in the population and the data suggest that the genomic clone was derived from the t4 apo-E allele, whereas the cDNA clones were derived from the €3 apo-E allele.S1 nuclease protection and primer extension experiments allowed the tentative assignment of the cap site of apo-E mRNA to the A approximately 44 base pairs upstream of the GT that begins the first intron.The sequence TATAATT was identified beginning 33 base pairs upstream of the proposed cap site and is presumably one element of the apo-E promoter.Finally, the apo-E gene was mapped in the human genome to chromosome 19 through the use of DNA probes and human-rodent somatic cell hybrids.Apo-E is one of the protein constituents of plasma lipoprotein particles (1).It mediates lipoprotein catabolism by binding to high affinity cell surface receptors (2, 3).Mature apo-E is a 299-amino acid polypeptide of known primary amino acid sequence (4).High resolution 2-dimensional polyacrylamide gel electrophoresis of human plasma apo-E reveals several isoproteins which differ in both size and/or charge (5,6).These isoproteins are the result of both common genetic * The costs of publication of this article were defrayed in part by the payment of page charges.