Endoplasmic Reticulum

ID #1988

I have question about the signals that get proteins encorporated into the mebranes. If it is an amino terminal signal then it requires that the signal sequence be cleaved. Is it relevant as to which what protein cleaves the peptide? Also, if it is an internal signal sequence, the signal sequence is not cleaved. Is this correct?

There's only one enzyme in the ER that removes amino terminal signal sequences, and that's Signal Peptidase. And yes, if it's an internal signal sequence, it remains part of the protein and becomes a membrane-spanning region.


    Also, I know that in order to get to ER membrane and be translated there by ribosomes there must be a peptide signal sequence that binds to SRP. This signal must still be present. Does it precede either the amino terminal or internal signal sequence and then get cleaved off or are the amino terminal and internal signal sequences themselves the signal sequence that binds to SRP and causes translation to occur at the ER?


Definitely the latter. It's the signal peptide itself, whether at the amino terminus or elsewhere, that gets bound by SRP and directed to a translocon.

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