In tailing, adenylate residues are added at 3 end

Options

A. With the help of gyanyl transferase
B. In a template independent manner
C. With the help of methyl transferase
D. Of hn- RNA of E.coil

Answer

### Step-by-Step Solution:

1. **Understanding Tailing**:
- Tailing refers to the addition of adenylate (A) residues at the 3' end of the precursor heterogeneous RNA (HnRNA) during the processing of mRNA.

2. **Identifying the Ends of HnRNA**:
- The HnRNA has a 5' end and a 3' end. Tailing specifically involves modifications at the 3' end.

3. **Role of Enzymes**:
- Tailing does not involve a template; it is a template-independent process. This means that the addition of adenylate residues does not require a complementary strand of RNA or DNA.

4. **Amount of Adenylate Residues**:
- Typically, 200 to 300 adenylate residues are added to the 3' end of the HnRNA during the tailing process.

5. **Distinguishing from Capping**:
- Capping is a different process where unusual nucleotides (specifically a guanosine monophosphate) are added to the 5' end of the HnRNA, facilitated by the enzyme guanyltransferase.

6. **Evaluating Options**:
- The first option incorrectly states that guanyltransferase is involved in tailing.
- The second option correctly states that adenylate residues are added in a template-independent manner, making it the correct answer.
- The third option incorrectly mentions methyl transferase, which is involved in capping, not tailing.
- The fourth option incorrectly refers to HnRNA of E. coli, which is not relevant to the question.

7. **Conclusion**:
- The correct answer is option 2, as it accurately describes the process of tailing.