Lecture 2

Forms from rough ER (when disrupted) -can be used to be studied in vitro -ER can’t be isolated as they turn into microsomes when they’re disrupted

-Exploits

Rabbit reticulocyte has high concentration machineriy

-be used to confirm mobility of protein -bind particular antibody -study co-translation translocation to ER

-Hydrophobic Stretch with 1 or so basic residue (Arg or Lys) -Ala-X-Ala|Y cleavage site of small uncharged residue

-Drives co-translation translocation of protein into ER lumen -SRP helps stop translation and target to ER -recognize by Sec61 which is part of the translocon

-recognizes ER signal sequence -Is recognized by SRP Receptor on surface of ER -stops translation -requires Ras-like GTPase to recognize SRP and SR

-drives POST-translational translocation into ER -normally in ATP form but becomes hydrolyzed to ADP as peptide becomes incorporated ADP -pulls peptide out of translocon ratchet motion -ADP to ATP releases the peptide

-hydrophobic anchor that acts as stop-transfer sequence -uncleaved signal sequence would lead to continuous growth and just end up out to the cytosol

acts as both as signal and anchor sequence

has a plug and lateral gate which allows transmembrane proteins to fold laterally into the membrane