Targeting sequences at the N-terminus of proteins direct translation across the ER, and act as signals for import to the nucleus, mitochondrion and chloroplasts. Sequences at the C-terminus control traffic through the ER and the Golgi and to peroxisomes.
Glycosylation is directed by signal sequences that act as targets for N-linked glycosylation in the ER and O-linked glycosylation in the Golgi apparatus. Glycosylation and remodelling of polysaccharides is important in controlling protein folding and release from the ER, and in affecting the stability and function of the completed glycoprotein.
Lipidation affects the ways in which proteins attach or partition to membranes, and may also contribute to sorting.