Intestinal apolipoprotein B differs from hepatic apolipoprotein B because the intestinal transcript undergoes a post-transcriptional change that creates a UAA stop codon, producing the truncated apoB-48 protein. What is this change?

• A Skipping of an exon containing the full-length coding region
• B Alternative use of a downstream polyadenylation signal
• C Enzymatic deamination of a specific cytidine to uridine within the coding sequence ✓
• D Proteolytic cleavage of the full-length protein by a luminal peptidase

Explanation

ApoB mRNA editing in the intestine is carried out by the APOBEC1 deaminase complex, which converts a single cytidine at codon 2153 to uridine. The CAA glutamine codon becomes UAA, a stop codon, yielding apoB-48 (48 percent of full length) without any alteration of the gene or the primary transcript pattern. ApoB-48 is a translational product of edited mRNA, not a proteolytic fragment, which distinguishes it from other truncated plasma proteins.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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