rough endoplasmic reticulum lecture 19 bsci 420/421oct 16, 2002 “if you want the rainbow, you...
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Rough Endoplasmic Reticulum
Lecture 19 BSCI 420/421 Oct 16, 2002
“If you want the rainbow, you gotta put up with the rain”-Dolly Parton
Evidence for the signal hypothesis:
1. Without signal sequences, proteins are not imported into RER.(Protease protection assay)
2. When signal sequences are added to a gene coding for a normally cytosolic protein, the polypeptide it makes is incorporated into RER.
3. A different sized (smaller) polypeptide is made in RER than when the same mRNA is translated on free polysomes in anin vitro system (reticulocyte lysate wo RER).
The ER Signal is a sequence of about 10 hydrophobic AAsThat becomes anchored in the membrane by hydrophylic AAsOn either side. E.g.:Ser-leu-leu-leu-val-gly-Ile-leu-phe-trp-ala-thr near the NH2 terminal
The signal sequence initially binds to a RNP particle called theSignal Recognition Particle (SRP).