You are studying the activities of the apolipoproteins, apoB-48 and apoB-100. Both of these proteins are encoded by the same gene; yet apoB-48 is primarily expressed in the intestine, while apoB-100 expression is restricted to the liver. Which of the following is the most likely molecular process accounting for this difference in gene expression?
A) different initiation codons
B) DNA methylation
C) gene duplication
D) reiterated sequences
E) RNA editing

Question

Quizplus · Accepted Answer

RNA editing is the process that results in the production of apoB-48 in the intestine and apoB-100 in the liver from the same gene. In the intestine, a specific cytidine to uridine change in the mRNA results in a premature stop codon, leading to the shorter apoB-48 protein.  RNA editing in mammals involves the deamination of adenine (A) to produce inosine (I) in pre-mRNAs. The process of A-to-I editing is catalyzed by ADARs (ADAs acting on RNA). In some pre-mRNAs this alters splicing; in some it alters codon(s). RNA editing also occurs to convert C to U. A C-to-U edit in the gene for apolipoprotein B leads to tissue-specific generation of apoB- 48 in intestines, whereas, the nonedited mRNA makes apoB-100 in liver.

You Are Studying the Activities of the Apolipoproteins, ApoB-48 and ApoB-100