Editing Microsome (section)

== Signal Hypothesis ==
The Signal Hypothesis was postulated by [[Günter Blobel]] and [[David D. Sabatini|David Sabatini]] in 1971, stating that a unique peptide sequence is encoded by mRNA specific for proteins destined for translocation across the ER membrane. This peptide signal directs the active ribosome to the membrane surface and creates the conditions for transfer of the nascent polypeptide across the membrane. The generalization of the Signal Hypothesis to include signals for every organelle and location within the cell had an impact far beyond illuminating  the targeting of secretory proteins, as it introduced the concept of 'topogenic' signals for the first time. Before the Signal Hypothesis, it was almost inconceivable that information encoded in the polypeptide chain could determine the localization of proteins in the cell.<ref name="matlin">{{cite journal |last1=Matlin |first1=S. Karl |title=Spatial expression of the genome: the signal hypothesis at forty |journal=Nature Reviews Molecular Cell Biology |date=13 April 2011 |volume=12 |issue=5 |pages=333–340 |doi=10.1038/nrm3105 |pmid=21487438 |s2cid=37896698 }}</ref>