You want to better understand protein disulfide isomerase (PDI) localization and function for generating protein disulfide bonds. You create two different GFP-fusion constructs to express and monitor tagged PDI in the cell, PDI:GFP and GFP:PDI, where GFP sequence has been added to either the C-term or N-term of PDI, respectively. After you transfect different cell populations with the two constructs, you test for PDI transgene protein expression by anti-GFP Western Blot and then examine localization by microscopy. You know that PDI encodes for a 57 kDa protein and GFP expresses at 27 kDa. You are surprised to see that while both protein fusion constructs are expressed at the expected molecular weight and at similar levels, you get different results in localization…!?

Explain what you observe, and why you recovered similar protein expression but distinct localization for the two PDI constructs.