Suppose you are studying a mutant that you know is impaired in secretion, but you do not know the exact nature of the defect. You analyze the sugar content of some of the proteins purified from the mutant that you know should be N-glycosylated and find that fucose, galactose, and sialic acid residues are absent. Instead, only N-acetylglucosamine and mannose residues are evident. Where do you think the defect in secretion lies?