Two enzymes responsible for restricting the growth of
bacteriophage in E . Coli were isolated . One was methylase and
other was a restriction endonuclease. What is the significance of methylase ?

Options

A. Able to cut the DNA of bacteriophage at specific site
B. Able to of remove the methyl group and hence prevent the action of restriction of endonuclease on host DNA
C. Protection of host DNA from the action of restriction endonuclease
by adding methyl group to one or two bases usually within the sequences recognized by restriction enzyme
D. Able to ligate the two cohesive ends of DNA molecule

Answer

To answer the question regarding the significance of methylase in the context of E. coli and its interaction with bacteriophages, we can break down the solution as follows:

### Step-by-Step Solution:

1. **Understanding the Role of Methylase**:
- Methylase is an enzyme that adds methyl groups to specific sites on DNA. This process is known as methylation.

2. **Distinguishing Between Methylase and Restriction Endonuclease**:
- It is important to differentiate between the roles of methylase and restriction endonuclease. While restriction endonucleases cut DNA at specific sequences, methylases do not cut DNA; instead, they modify it by adding methyl groups.

3. **Protection of Host DNA**:
- The primary significance of methylase in E. coli is to protect the host DNA from being degraded by restriction endonucleases. By adding methyl groups to specific bases in the DNA, methylase prevents the restriction endonucleases from recognizing and cutting the host DNA.

4. **Mechanism of Action**:
- Methylation typically occurs at specific sequences recognized by restriction enzymes. When the host DNA is methylated, the restriction enzymes cannot bind to or cut the DNA, thereby providing a protective mechanism against foreign DNA, such as that from bacteriophages.

5. **Conclusion**:
- The correct statement regarding the significance of methylase is that it protects the host DNA from the action of restriction endonucleases by adding methyl groups to one or two bases within the sequences recognized by these enzymes.

### Final Answer:
The significance of methylase is that it protects the host DNA from the action of restriction endonucleases by adding methyl groups to specific bases, thereby preventing the enzymes from recognizing and cutting the DNA.