In the search for the biochemical basis of the control of glycosylation of cell surface carbohydrates, revertant clones were isolated from previously characterized wheat germ agglutinin-resistant clones of B16 mouse melanoma cells by selection for resistance to Lotus tetragonolobus lectin or to ricin. Comparison of the wheat germ agglutinin-resistant clones with the parent and revertant clones indicated that this phenotype was correlated with an increased sensitivity to the Lotus lectin, a 60- to 70-fold increase in alpha 1 leads to 3 fucosyltransferase activity and a decreased sialic acid content of the N-glycosidic chains of glycoproteins. The results suggest a novel type of control mechanism for lectin resistance, an increase in a glycosyltransferase activity. The presence of alpha 1 leads to 3 bound fucose on N-acetylglucosamine residues would interfere with the addition of sialic acid by alpha 2 leads to 3 linkages to galactose residues in the carbohydrate units, and this change could explain the resistance to wheat germ agglutinin and the increased sensitivity to the Lotus lectin. A change in a regulatory gene for the fucosyltransferase as a possible primary cause for the changed phenotype is discussed.

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