Topogenic sequence
A topogenic sequence is a collective term used for a peptide sequence present at nascent proteins essential for their insertion and orienting in cellular membranes. The sequences are also used to translocate proteins across various intracellular membranes,<ref name="robinson_role">Template:Cite journal</ref> and ensure they are transported to the correct organelle after synthesis.<ref name="gould_plastid">Template:Cite journal</ref> The position of the sequence may be at the end, e.g. N-terminal signal sequence, or in mid parts of the nascent protein, e.g. stop-transfer anchor sequences and signal-anchor sequences.<ref>Template:Cite book</ref> If the sequence is at the end of the polypeptide, it is cleaved off after entering the ER-lumen (via a translocon) by a signal peptidase, and subsequently degraded.
As an example, the vast majority of all known complex plastid preproteins (an 'unactivated' protein) encoded in the nucleus possess a topogenic sequence.<ref name=gould_plastid />