Question

Which of the following is NOT a likely ER signal sequence recognized by the signal-recognition particle? All sequences are written with their N-terminus on the left.

A. Met-Lys-Leu-Ser-Leu-Val-Ala-Ala-Met-Leu-Leu-Leu-Leu-Ser-Ala-Ala-Arg-Ala
B. Met-Glu-Met-Phe-Gln-Gly-Leu-Leu-Leu-Leu-Leu-Leu-Leu-Leu-Ser-Met-Gly-Gly-Thr-Trp-Ala
C. Met-Lys-Ala-Lys-Leu-Leu-Val-Leu-Leu-Tyr-Ala-Phe-Val-Ala-Gly-Asn
D. Met-Met-Ala-Ala-Gly-Pro-Arg-Thr-Ser-Leu-Leu-Leu-Ala-Phe-Ala-Leu-Leu-Cys-Leu-Pro-Trp-Thr-Gln-Val-Val
E. Met-Leu-Ser-Leu-Arg-Gln-Ser-Ile-Arg-Phe-Phe-Lys-Pro-Ala-Thr-Arg-Thr-Leu-Ser-Ser-Arg-Tyr-Leu

Answer 1

Sequence E lacks the typical length and hydrophobic characteristics of an ER signal sequence, making it the least likely to be recognized by the signal recognition particle for targeting to the RER.

Step-by-step explanation:

In the process of protein folding, modification, and targeting, a signal sequence, typically at the N-terminus of a protein, is critical for determining the protein's cellular destination. Signal sequences are recognized by the signal recognition particle (SRP) that directs the ribosome to the rough endoplasmic reticulum (RER) for proteins destined for secretion or for incorporation into the endomembrane system.

The signal sequences are usually composed of a core of hydrophobic amino acids which are recognized by the SRP. After the synthesis is complete or as the protein is being synthesized, these sequences are removed. Based on the sequences provided, we need to identify the one which is least likely to be an ER signal sequence. Sequence E, Met-Leu-Ser-Leu-Arg-Gln-Ser-Ile-Arg-Phe-Phe-Lys-Pro-Ala-Thr-Arg-Thr-Leu-Ser-Ser-Arg-Tyr-Leu, appears to be less hydrophobic compared to the others and lacks the essential length and characteristics typically required for an ER signal sequence, making it the least likely to be recognized by the SRP.