HeLa cells were mock-transfected or transfected with siRNA to COG2 or COG4. 96 hours after transfection, HeLa cells, and CHO cells for control staining, were fixed, stained with GS-II-Alexa 594 or GNL-Alexa 647 lectins for 30 minutes and analyzed by wide-field fluorescent microscopy. The control HeLa cells and control CHO cells were negative for both lectins, indicating that plasma membrane localized glycoconjugates’ polysaccharide chains are completely mature. In cells depleted of either COG2 or COG4, the plasma membrane was extensively labelled with both GNL and GS-II lectins. Likewise, the plasma membranes of both ldlB and ldlC cells were also distinctly stained with GNL and GS-II. This indicates that the COG subunit knockdown cells express plasma membrane-localized glycoconjugates with an increased amount of terminal mannoses and GlcNAc.