You have genetically engineered green fluorescent protein (GFP) containing a KDEL sequence (GFP-KDEL).

Question

You have genetically engineered green fluorescent protein (GFP) containing a KDEL sequence (GFP-KDEL). When GFP-KDEL is expressed in normal human fibroblasts and examined using fluorescence microscopy, the fluorescence appears diffuse across the cytoplasm. How would you explain this observations given that KDEL is supposed to be an ER-specific sorting sequence? 

	A. This engineered GFP would not have a hydrophobic signal sequence to get it into the RER in the first place.
	B. The KDEL sequence would not be recognized because the protein is not in the right compartment.
	C. This engineered GFP would be synthesized on cytosolic ribosomes.
	Both A and B.
	A, B and C.

Answer 1

I think the answer is C. KDEL is suppose to be in the ER, however, since the question says a GFP incorporates the sequence, the cell would not be able to read the sequence, thereby synthesizing the GFP in cytosolic ribosomes.

I don't think A is the correct answer because the protein would not need hydrophobic signal sequence. Instead it would need a compatible sequence to associate with the receptor.

I don't think B is correct because the protein would be in the right compartment of the cell but would not be able to be recognized.