7.4.3 Soluble proteins destined for secretion or residence within the lysosomal and other EMs vacuolate lumens They are synthesized on membrane-bound ribosomes and across the er membrane and released into the er lumen 1. Signal hypothesis 1971, it was first suggested by Gunter Blobel and David Sabatini and 1975 was conformed by a serious of experiments about the study of secreted protein Ig light chain by Blobel and Doberstein. The signal hypothesis proposed that 1) mRna to be translated on membrane-bound ribosomes contain a unique set of codons just 3end of initiation site(2)the translation of these codons yields a unique sequence at the N-terminus of the growing polypeptide chain (called signal sequence)(3)the signal sequence triggers attachment of the ribosome to the membrane of rer and the movement of the nascent polypeptide into the cisternal space o of ER through a protein-lined, aqueous channel in ER membrane as it is being synthsized. that is, cotranslationally7.4.3 Soluble proteins destined for secretion or residence within the lysosomal and other EMS vacuolate lumens They are synthesized on membrane-bound ribosomes and across the ER membrane and released into the ER lumen. 1. Signal hypothesis 1971, it was first suggested by Günter Blobel and David Sabatini and 1975 was conformed by a serious of experiments about the study of secreted protein Ig light chain by Blobel and Doberstein. The signal hypothesis proposed that: (1) mRNA to be translated on membrane-bound ribosomes contain a unique set of codons just 3’end of initiation site (2) the translation of these codons yields a unique sequence at the N-terminus of the growing polypeptide chain (called signal sequence) (3) the signal sequence triggers attachment of the ribosome to the membrane of RER and the movement of the nascent polypeptide into the cisternal space of ER through a protein-lined, aqueous channel in ER membrane as it is being synthsized, that is, cotranslationally