<Li> Manufacture of secreted proteins, either secreted constitutively with no tag or secreted in a regulatory manner involving clathrin and paired basic amino acids in the signal peptide . </Li> <Li> Integral membrane proteins that stay embedded in the membrane as vesicles exit and bind to new membranes . Rab proteins are key in targeting the membrane; SNAP and SNARE proteins are key in the fusion event . </Li> <Li> Initial glycosylation as assembly continues . This is N - linked (O - linking occurs in the Golgi). <Ul> <Li> N - linked glycosylation: If the protein is properly folded, Oligosaccharyltransferase recognizes the AA sequence N X S or N X T (with the S / T residue phosphorylated) and adds a 14 - sugar backbone (2 - N - acetylglucosamine, 9 - branching mannose, and 3 - glucose at the end) to the side - chain nitrogen of Asn . </Li> </Ul> </Li> <Ul> <Li> N - linked glycosylation: If the protein is properly folded, Oligosaccharyltransferase recognizes the AA sequence N X S or N X T (with the S / T residue phosphorylated) and adds a 14 - sugar backbone (2 - N - acetylglucosamine, 9 - branching mannose, and 3 - glucose at the end) to the side - chain nitrogen of Asn . </Li> </Ul>

Which of the following are sometimes found attached to the endoplasmic reticulum