Tissue-specific differences in the role of RNA 3' of the apolipoprotein B mRNA mooring sequence in editosome assembly

Site-specific editing of apolipoprotein B (apoB) mRNA by the cytidine deaminase, APOBEC-1 is proposed to require interactions of auxiliary protein(s) with an eleven nucleotide element, the mooring sequence, located 3' of the C --> U editing site. An analysis of the RNA sequence dependence for protein-RNA interactions and editosome assembly in rat liver and the small intestine demonstrated that the mooring sequence was a minimal requirement for these interactions. Sequences 3' of the mooring sequence either interacted with 66 kDa and 44 kDa proteins or enhanced the interactions of these proteins with the mooring sequence. The data also suggested tissue-specific differences in the relative importance of the 3' cis-acting 'enhancer' elements in the efficiency or stability of editosome assembly. We propose that the previously demonstrated differences in apoB mRNA editing efficiency and its regulation in liver and intestine may in part be due to differences in auxiliary protein interactions with apoB mRNA 3' of the mooring sequence.