APOBEC1 Background Information Post-transcriptional editing of apolipoprotein B (apoB) mRNA is regulated by APOBEC1 (also designated human (or rat) small intestinal apolipoprotein B mRNA editing protein, HEPR, or REPR) in hepatic cells to achieve a steady state proportion of edited and unedited RNA molecules (1). APOBEC1 has conserved histidine and cysteine residues, that are identified as a Zn2+ binding motif in other cytidine deaminases (2-4). APOBEC1 is predominantly expressed in the adult small intestine but is also found in the stomach, colon and testis (2,3). APOBEC1 exists as a dimer and shows structural homology to some known mammalian and bacteriophage deoxycytidylate deaminases which exist as homopolymers (4). APOBEC1 may be involved in other aspects of RNA metabolism, independent of its role as an apoB RNA-specific cytidine deaminase (5).
