Question

What does I in restriction enzyme Hind \( \mathrm{S_2} \)I indicate?

• A. It cuts after the first nucleotide in the restriction site.
• B. It is the first enzyme isolated from strain \( \mathrm{S_2} \) of bacterium.
• C. Only one enzyme can be used to digest a plasmid from \( \mathrm{S_2} \) strain.
• D. Only one restriction enzyme has been isolated from this bacteria.

Hint:

The Roman numeral gives the order in which the enzyme was isolated from that strain.

Answer 1

The Correct Option is B

Step 1: Recall the naming rule:
A restriction enzyme name has parts. The first capital letter is the genus, the next two letters are the species, the next letter is the strain, and the Roman numeral shows the order of isolation.
For EcoRI: E for Escherichia, co for coli, R for strain RY13 and I for the first enzyme isolated from that strain.

Step 2: Apply to the given name:
In Hind \( \mathrm{S_2} \)I, the Roman numeral I means it was the first enzyme isolated from strain \( \mathrm{S_2} \) of the bacterium. So (B) is TRUE.

Step 3: Check the others:
(A) is FALSE. The numeral has nothing to do with the cut position. The enzyme cuts at a specific palindromic site.
(C) is FALSE. Many different enzymes can digest a plasmid.
(D) is FALSE. A strain can give several enzymes, which are numbered I, II, III and so on.

Final Answer:
I tells that it was the first enzyme isolated from strain \( \mathrm{S_2} \), which is option (B).