Apolipoprotein B messenger RNA editing: an update.

Apolipoprotein (apo) B mRNA editing consists of a C-->U conversion of the first base of the codon CAA encoding glutamine 2153 in apoB mRNA to UAA, a stop codon. The cDNA for an apoB mRNA editing protein was recently cloned in rat and human. The human protein contains 236 amino acid residues and exists as a homodimer. The editing protein edits apoB mRNA in vitro only in the presence of tissue complementation factors. There is a leucine-rich motif spanning residues 173-210 of the protein which may be involved in homodimer formation and/or interaction with complementation factors. The requirements for these factors support the existence of an editosome involved in apoB mRNA editing.