Amplification of the Gene for N-Acetylglucosaminyl Phosphate Transferase, an Enzyme Catalyzing an Early Step in Asn-Linked Glycosylation, in Chinese Hamster Ovary Cells Resistant to Tunicamycin

The observed increase in N-acetylglucosaminyl phosphate transferase activity in tunicamycin (TM)-resistant cells appeared to be specific for that enzyme. In the synthesis of asparaginyl glycoproteins by eukaryotic cells, the initial transfer of carbohydrate to asparagine residues of newly synthesized polypeptide chains occurs in the endoplasmic reticulum. TM-resistant cells were cultured in the presence of TM except for the last 14 days before membrane preparation. A summary of the glycosylation phenotype of TM-resistant cells grown without TM compared to wild-type and TM-resistant cells grown in TM is presented. Gene amplification has been demonstrated as a mechanism of overproduction of target enzymes in drug-resistant cells. The purification of these enzymes from normal cells has been tedious, and in most cases isolation of homogeneous enzyme has thus far been impossible. TM-resistant cells were cultured in the presence of TM except for the last 14 days before membrane preparation.