Question

The biochemical nature of Nuclear Localization Signal is?

• A. Sequence of amino acids
• B. Sequence of nucleotides similar to DNA
• C. Sequence of nucleotides similar to RNA
• D. Sequence of nucleosides

Hint:

An NLS is a peptide "ZIP code" on a protein, consisting of basic amino acids (Lysine and Arginine). This sequence is recognized by importins to allow passage through the nuclear pore.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Proteins synthesized in the cytoplasm that are destined for the nucleus must be actively transported across the nuclear envelope.
This targeted transport is directed by a specific signal sequence within the protein's primary structure.

Step 2: Detailed Explanation:
The Nuclear Localization Signal (NLS) is a short stretch of amino acids within a protein that serves as a molecular address tag.
It is recognized by cytosolic receptor proteins called importins, which guide the target protein through the nuclear pore complex into the nucleus.
Characteristics of NLS:
1. It is composed entirely of amino acids, usually rich in basic, positively charged residues like lysine and arginine (such as the classic PKKKRKV sequence of the SV40 large T-antigen NLS).
2. Unlike mitochondrial targeting signals, the NLS is not cleaved after transport, allowing the protein to re-enter the nucleus if it is exported or if the nuclear envelope breaks down during mitosis.
Because it is a peptide segment of the nuclear protein itself, its biochemical nature is a sequence of amino acids, not nucleotides or nucleosides.

Step 3: Final Answer:
The biochemical nature of the Nuclear Localization Signal is a sequence of amino acids, corresponding to option (A).