RNA EDITING OF THE APOLIPOPROTEIN-B GENE - A MECHANISM TO REGULATE THE ATHEROGENIC POTENTIAL OF INTESTINAL LIPOPROTEINS

Apolipoprotein B (apo B) circulates in two distinct isomorphic forms, each the product of a single gene. The larger form, referred to as apo B-100, is the major protein of plasma low-density lipoproteins (LDLs) and is synthesized by the human liver The smaller form, referred to a s apo B-48, is produced in the small intestine as a result of a site-s pecific cytidine deamination, which alters a CAA codon, encoding gluta mine in the unedited (apo B-100) mRNA to UAA, which specifies an in-fr ame stop codon. Apo B-48 lacks the domains involved in LDL receptor in teraction and in complex formation With apolipoprotein(a). DNA sequenc e analysis of the gene that mediates this site-specific cytidine deami nation suggests that apo B mRNA editing is an evolutionary adaptation to limit the atherogenic potential of intestinal lipoproteins.