Correct option is A
Explanation -
This is about nuclear localization signals (NLS), which are short stretches of amino acids that help proteins enter the nucleus via nuclear pore complexes.
Option a: -Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val-
This sequence is rich in basic amino acids: Lysine (Lys, K) and Arginine (Arg, R). Such sequences are known as classical nuclear localization signals (cNLS). Specifically, this sequence resembles the SV40 large T-antigen NLS, a well-studied monopartite NLS:
PKKKRKV → equivalent to Lys-Lys-Lys-Arg-Lys-Val.
These are recognized by importin-α which transports the protein into the nucleus.
So, correct answer for nuclear import.
Incorrect Options-
Option b: -Leu-Ala-Leu-Lys-Leu-Ala-Gly-Leu-Asp-Ile-
This sequence has mostly hydrophobic and neutral amino acids. It resembles signal sequences that target proteins to the endoplasmic reticulum (ER) or other organelles. So, not typically involved in nuclear import.
Option c: -Ser-Lys-Leu-COO-
A short tripeptide ending with Leu, resembling the peroxisomal targeting signal type 1 (PTS1).
Common PTS1: Ser-Lys-Leu (SKL) at the C-terminus directs proteins to peroxisomes, not the nucleus.
Option d: -Lys-Asp-Glu-Leu-COO-
This sequence matches the KDEL signal: Lys-Asp-Glu-Leu, found at the C-terminus of ER-resident proteins. The KDEL sequence ensures retention in the endoplasmic reticulum, not nuclear import.
Final Answer- Option a - Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val-
