In vitro reconstitution of apolipoprotein B RNA editing activity from recombinant APOBEC-1 and McArdle cell extracts.

Apolipoprotein B (apoB) RNA editing activity involves a site-specific cytidine to uridine transition catalyzed by a cytidine deaminase, APOBEC-1, in the context of a multi-protein-containing editosome. In the absence of yet to be characterized "auxiliary" proteins, APOBEC-1 lacks RNA editing capacity. Recombinant APOBEC-1 has been engineered to bind nickel resin and used in affinity chromatography of the auxiliary proteins from McArdle rat hepatoma cell extracts. We demonstrate activation of APOBEC-1 RNA editing activity under these conditions through the association of a subset of extract proteins having approximate molecular masses of 145, 87, 75, 66, 61, and 50 kDa and a heterogeneous grouping of 45- to 35-kDa proteins. These data suggest that the components of the editosome can be partially purified from extracts through APOBEC-1 affinity chromatography.