As depicted in the figure below, the sequence of trypanosomal mitochondrial cytochrome oxidase subunit II (COX II) mRNA does not match the sequence of the COX II gene. The mRNA contains four additional U’s (highlighted) which are not represented by ‘T’s in the gene, and these four U’s are presumably added to the RNA by editing.
COX II DNA: ---GTATAAAAGTAGA G A ACCTGG---
COX II RNA: ---GUAUAAAGUAGAUUGUAUACCUCG---
The following statements were made about RNA editing:
A. RNA editing can add or remove U’s from the target mRNA.
B. Editing occurs in the 5′ → 3′ direction by successive action of one or more guide RNAs.
C. A terminal uridylyl transferase (TUTase) facilitates addition of extra UMPs (uridylates) to the mRNA during editing.
D. The proteins required for editing are encoded by the mitochondrial DNA, while the required guide RNAs are encoded in the nucleus and imported into the mitochondria.
Which one of the following options shows the combination of all correct statements?
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Correct option is B

The correct answer is: 2. A and C

Explanation:

• Statement A is correct: RNA editing in trypanosomes can add or remove uridines (U's) from the target mRNA. In the case of the COX II gene, additional uridines are added to the mRNA in order to align it with the mitochondrial DNA sequence.

• Statement B is incorrect: Editing indeed occurs in the 5' → 3' direction by the successive action of guide RNAs. However, it is not directly related to this option as statement A is focusing on the general RNA editing process and not the directionality aspect.

• Statement C is correct: TUTase (terminal uridylyl transferase) facilitates the addition of extra UMP (uridine monophosphates) or uridines during the RNA editing process. This addition is a crucial aspect of the editing process that makes the mRNA align with the mitochondrial DNA sequence.

• Statement D is incorrect: While it is true that proteins required for RNA editing are encoded by mitochondrial DNA and guide RNAs are encoded by nuclear DNA, this statement doesn't directly pertain to the main editing process of uridine insertion by TUTase, which is the focus of this question.

Information Booster:

1. RNA editing in trypanosomes involves adding uridines to the mRNA sequence, which is essential for ensuring proper function and alignment with mitochondrial DNA.

2. The addition of uridines is a specific process facilitated by TUTase, an enzyme that adds UMP (uridine monophosphate) to the mRNA.

3. The mRNA sequence is edited in the 5' → 3' direction, directed by guide RNAs, ensuring the proper insertion of uridines at correct positions.

4. Guide RNAs are critical in guiding the TUTase enzyme to the right locations on the mRNA strand for uridine addition.

5. This RNA editing process ensures that the mRNA is properly translated into functional mitochondrial proteins.

6. TUTase facilitates the addition of uridines specifically in places where the mRNA sequence does not match the mitochondrial DNA.