Editing Proteolysis (section)

==== Removal of N-terminal methionine ====
The initiating methionine (and, in bacteria, [[fMet]]) may be removed during translation of the nascent protein. For ''[[Escherichia coli|E. coli]]'', fMet is efficiently removed if the second residue is small and uncharged, but not if the second residue is bulky and charged.<ref>{{cite journal |author1=P H Hirel |author2=M J Schmitter |author3=P Dessen |author4=G Fayat |author5=S Blanquet |title=Extent of N-terminal methionine excision from Escherichia coli proteins is governed by the side-chain length of the penultimate amino acid |journal=Proc Natl Acad Sci U S A |volume=86|issue=21 |pages=8247–51 |year=1989 |pmid=2682640 |pmc=298257 |doi=10.1073/pnas.86.21.8247|bibcode=1989PNAS...86.8247H |doi-access=free }}</ref> In both [[prokaryotes]] and [[eukaryotes]], the exposed N-terminal residue may determine the half-life of the protein according to the [[N-end rule]].