Question

In the nomenclature of RENs (restriction endonuclease) Hind III, III stands for
A. Genus name
B. Species name
C. Order of discovery
D. Strain of the organism

Answer 1

Hint: Hind III is a type II site-specific deoxyribonuclease restriction enzyme isolated from Hemophilus influenzae that cleaves the DNA palindromic sequence AAGCTT in the presence of the cofactor Mg2+ via hydrolysis.
Hind III restrictions process results in the formation of overhanging palindromic sticky ends.

Complete answer: Restriction enzymes are named based on the organism in which they were discovered.
1. The enzyme Hind III has isolated from Haemophilus influenzae, strain Rd.
2. The first three letters of the name are italicized because they abbreviate the genus and species names of the organism.
3. The fourth letter typically comes from the bacterial strain designation.
4. The Roman numerals are used to identify specific enzymes from bacteria that contain multiple restriction enzymes.

Additional information: There are three classes of restriction enzymes.
They are type I II, and III.
1. Type I restriction systems consist of a single enzyme that performs both modification (methylation) and restriction activities.
2. Type III restriction systems have separate enzymes for restriction and methylation, but these enzymes share a common subunit. These enzymes recognize specific DNA sequences, but cleave DNA at random sequences approximately twenty-five bp from the recognition sequence.
3. Type I nor type III restriction systems have not found much application in recombinant DNA techniques.
4. Type II restriction enzymes, in contrast, are heavily used in recombinant DNA techniques. Type II enzymes consist of single, separate proteins for restriction and modification.
One enzyme recognizes and cuts DNA, the other enzyme recognizes and methylates the DNA.
5. Type II restriction enzymes cleave the DNA sequence at the same site at which they recognize it. Cleaving a single piece of DNA with multiple restriction enzymes creates a "DNA fingerprint."

So, the answer is C. Order of discovery.

Note: The Roman numeral indicates the order in which restriction enzymes were discovered in a particular strain.