Ribosomes targeted to ER by signal sequence at
NH2-terminus of polypeptide
• Protein synthesis starts on free ribosomes
Cotranslational translocation:
• Proteins translocated into ER during synthesis on
membrane-bound ribosomes.
Posttranslational translocation:
• proteins are translocated into ER after translation completed
on free ribosomes; Hsp70 Chaperone proteins
Figs. 8.22,27