Structure of the human apolipoprotein B gene

Human apolipoprotein B100 cDNA is 14 kilobases in length and encodes a 4563-amino acid precursor protein. The corresponding human gene has been isolated as a series of overlapping lambda clones and extends over 43 kilobases. The gene comprises 29 exons and 28 introns. The distribution of introns is extremely asymmetrical, most of them appearing in the 5'-terminal one-third of the gene. Although most of the exons fall within the normal size limits for mammalian genes, two are unusually long: 1906 and 7572 base pairs. The latter exon is by far the longest reported for a vertebrate gene.