Question

3. You modify GDP (green fluorescent protein) to contain a signal sequence you believe is a novel ER import signal at the N-terminus and a stop transfer sequence 43 amino acids from the N terminal import signal. When this protein is expressed in cells, you see 70% GFP in the cytoplasm and the remainder in the ER. You assume GFP import is occurring. However you cannot rule out some GFP might not fold properly even though it is fluorescent, perhaps providing the 30% GFP "glow" in the cytoplasm.

1. Would cytoplasmic injection of an antibody that binds tightly to the GFP resolve how much GFP is really in the ER? Briefly explain why or why not.
2. Instead of a., you injected an antibody that binds tightly only to the ER signal sequence on the GFP protein. Would this experiment’s results resolve how much GFP is really in ER and/or cytoplasm? Briefly explain why or why not.