1. Rough Endoplasmic Reticulum Lecture 19 BSCI 420/421Oct 16, 2002 “If you want the rainbow, you gotta put up with the rain” -Dolly Parton

2. Fluorescent Micrographs of ER

3. TEMs of RER

6. F37 Free And Membrane- Bound R-somes

7. The signal hypothesis: That an ER signal sequence in the nacent Polypeptide chain directs

8. 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 an in vitro system (reticulocyte lysate wo RER).

9. The ER Signal is a sequence of about 10 hydrophobic AAs That becomes anchored in the membrane by hydrophylic AAs On 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 the Signal Recognition Particle (SRP).

10. How the SRP directs ribosomes to the RER

12. Evidence for an aqueous pore thru which the polypeptide Passes into the ER

13. A soluble protein released into the ER lumen to be secreted

14. A single-pass membrane protein

15. Hydrophobicity plot of rhodopsin, a 7-pass transmembrane protein