Summary

• Targeting of newly synthesized proteins is an integral component of protein synthesis.

• In prokaryotes, targeting is usually achieved by an N-terminal signal sequence of about 20 mostly hydrophobic amino acids.

• In eukaryotes, targeting is more complex due to the large number of different cellular compartments:
• Nuclear targeting via the nuclear pore using a nuclear localization signal.
• ER targeting (secretory pathway) via N-terminal signal sequences using SRPs with subsequent attachment to the ER,
• Followed by transport to the Golgi complex

• Protein degradation of damaged or obsolete proteins is carried out
• by lysosomes, vesicles filled with degradating enzymes
• in a ubiqutin-dependent process by specific proteases in a large cytosolic complex called the proteasome.

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