Editing Protein targeting (section)

===Post-translational translocation===
Even though most secretory proteins are co-translationally translocated, some are translated in the [[cytosol]] and later transported to the ER/plasma membrane by a post-translational system. In prokaryotes this process requires certain cofactors such as [[SecA]] and SecB and is facilitated by Sec62 and Sec63, two membrane-bound proteins.<ref>{{cite journal | vauthors = Rapoport TA | title = Protein translocation across the eukaryotic endoplasmic reticulum and bacterial plasma membranes | journal = Nature | volume = 450 | issue = 7170 | pages = 663–9 | date = November 2007 | pmid = 18046402 | doi = 10.1038/nature06384 | bibcode = 2007Natur.450..663R | s2cid = 2497138 }}</ref> The Sec63 complex, which is embedded in the ER membrane, causes hydrolysis of ATP, allowing chaperone proteins to bind to an exposed peptide chain and slide the polypeptide into the ER lumen. Once in the lumen the polypeptide chain can be folded properly. This process only occurs in unfolded proteins located in the cytosol.<ref name="Lodish-2008">{{cite book| vauthors = Lodish H, Berk A, Kaiser C, Krieger M, Bretscher A, Ploegh H, Amon A, Martin K |title=Molecular Cell Biology|date=2008|publisher=W.H. Freeman and Company|isbn=978-1-4641-8339-3|edition=8th|location=New York|pages=591–592}}</ref>

In addition, proteins targeted to other cellular destinations, such as [[mitochondria]], [[chloroplasts]], or [[peroxisomes]], use specialized post-translational pathways. Proteins targeted for the nucleus are also translocated post-translationally through the addition of a [[Nuclear localization signal|nuclear localization sequence]] (NLS) that promotes passage through the [[nuclear envelope]] via [[nuclear pore]]s.<ref>{{cite journal | vauthors = Lange A, Mills RE, Lange CJ, Stewart M, Devine SE, Corbett AH | title = Classical nuclear localization signals: definition, function, and interaction with importin alpha | journal = The Journal of Biological Chemistry | volume = 282 | issue = 8 | pages = 5101–5 | date = February 2007 | pmid = 17170104 | pmc = 4502416 | doi = 10.1074/jbc.R600026200 | doi-access = free }}</ref>