A sequence of 16 to 20 amino acids at the N-terminus of some eukaryotic proteins that determines their ultimate destination. Proteins that are made and function in the cytosol lack leader sequences. Proteins destined for specific organelles require signal sequences appropriate for each organelle. The leader sequence for a protein destined to enter the endoplasmic reticulum always contains hydrophobic amino acids that become embedded in the lipid bilayer membrane, and it functions to guide the nascent protein to a receptor protein that marks the position of a pore in the membrane. Once the protein passes into the cysternal lumen through the pore, the leader segment is cleaved from the protein. For example, the leader sequence peptide of an interferon protein allows the cell to secrete the interferon, but is removed from the mature molecule during the secretion process. All of the leader sequences of mitochondrial proteins investigated thus far are strikingly basic, but otherwise have no similarities. The leader sequence peptide is also known as the signal peptide (q.v.). See antihemophilic factor, receptor-mediated translocation.
Subjects: Genetics and Genomics.