18]Mammalian RNA Editing

Abstract

This chapter focuses on the concept of mammalian RNA editing. It discusses methods for the characterization of Apolipoprotein B ( apoB) mRNA editing. ApoB mRNA editing occurs in the small intestine in all mammals that have been examined. In the liver of most mammals, including humans, apoB mRNA remains unedited. However, in a few species, notably rats and mice, editing also occurs in the liver. A sequence-specific hydrolytic deamination of cytidine-6666 appears to mediate the editing reaction. Editing requires a multiprotein component complex called an “editosome.” A catalytic component of the editing machinery has been cloned. This component has been named “apobec-1.” In characterizing apoB mRNA editing, two major questions need to be addressed: (1) within a sample of RNA (with apoB mRNA as one of its components), what proportion of the apoB mRNA is in the edited form, and (2) what is the editing activity in a particular sample (of tissue extract or cloned editing components expressed in vitro ). The experimental approaches used to answer these questions are described in the chapter. It describes the assays for measuring the degree of editing in RNA sample and in vitro assays for Apolipoprotein B mRNA editing activity.