C-to-U editing has only been identified in one protein. What is that protein called?
The correct answer and explanation is:
The protein in which C-to-U editing has been identified is apolipoprotein B (ApoB). This is an important protein that plays a central role in lipid metabolism and the formation of lipoproteins, which transport cholesterol and triglycerides in the bloodstream.
Explanation:
C-to-U editing refers to a specific form of RNA editing where a cytosine (C) nucleotide is changed into a uracil (U) in the RNA sequence. This process is catalyzed by enzymes known as ADARs (adenosine deaminases acting on RNA).
In the case of ApoB, the C-to-U editing occurs in the mRNA transcript of the ApoB gene. The modification of a single cytosine to uracil leads to a change in the encoded protein. Specifically, this editing occurs at a particular site in the ApoB mRNA, which results in the creation of two different forms of the protein: ApoB-100 and ApoB-48.
- ApoB-100 is a full-length protein, composed of 100% of the amino acid sequence encoded by the mRNA.
- ApoB-48 is a truncated version, produced because of the C-to-U editing event. The mRNA editing leads to a premature stop codon, which causes the translation machinery to halt early, producing a shorter version of the protein.
This editing event is crucial for regulating the function of lipoproteins, particularly in the liver and intestines. ApoB-48, for example, is primarily found in chylomicrons in the intestines, while ApoB-100 is involved in the formation of very low-density lipoproteins (VLDL) in the liver.
The discovery of C-to-U editing in ApoB highlights its importance in post-transcriptional regulation and protein diversity, showing how RNA modifications can control the function and structure of proteins without altering the DNA sequence.