Question

4. Predict the membrane orientation of a protein that is synthesized with an N-terminal (cleaved) signal sequence, followed by a stop-transfer sequence.

• The protein spans the membrane once, with the N-terminus in the cytosol, and the C-terminus in the ER lumen

• The protein spans the membrane once, with the C-terminus in the cytosol, and the N-terminus in the ER lumen.

Answer 1

Answer: The protein spans the membrane once, with the C terminus in the cytosol, and the N terminus in the ER lumen

A stop transfer sequence in an internal peptide sequence within a protein that stops the process of translocation into the ER, makes the protein slip through a side opening of the translocon and get inserted into the ER membrane. So the protein spans the membrane once. Since translocation had begun with the N terminus, hence N terminus remains inside the ER whereas the C terminus remains in the cytosol.

answered by: anonymous