Which of following could be a description for HRIET1?
(A) A protein found in the blood that plays a role in the immune system
(B) A protein found in the Golgi apparatus that helps tether vesicles
(C) A protein found in the nucleolus aiding in ribosome assembly
(D) A protein found in the cytosol serving as a cytoskeletal anchor

Proteins often need the equivalent of a shipping label so that they can be sent intracellularly or extracellularly to the correct location. These labels are typically found in three forms: signal sequences, target signals, or localization signals. A signal sequence is a stretch of hydrophobic amino acid residue that is only located within polypeptides destined to fold into EITHER extracellular proteins, intermembrane proteins that will anchor to the cell surface, or proteins that will be members of the secretory pathway that packs and ships things towards the cell surface. A targeting signal is a sequence that identifies the proteins of the secretory pathway. A localization signal is a sequence that labels proteins that are destined to go to specific organelles (that are not part of the secretory pathway). The table below shows seven eukaryotic proteins, and the sequences have been identified in each.

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Protein HRIET1 HAZL2 NUH8 K8TE TELEE TMSDG LNACT Signal Sequence X X X X Targeting Signal X X X Localization Sequence X X