Anchoring of membrane proteins via phosphatidylinositol is deficient in two classes of Thy-1 negative mutant lymphoma cells.

Recent evidence shows that mature Thy-1 glycoprotein lacks amino acids 113-143 predicted from the cDNA sequence and is anchored to the plasma membrane by a phosphatidylinositol-containing glycolipid attached to amino acid 112. Previously characterized Thy-1-deficient mutant lymphoma lines of complementation classes A and E were analysed. They make detergent binding Thy-1 precursors but, in contrast to wild-type, the detergent binding moiety cannot be removed by phospholipase C. Moreover, tryptophan which only occurs at position 124 is incorporated into mutant but not parental Thy-1. This suggests that the mutants make a Thy-1 precursor of 143 amino acids but fail to replace its C-terminal end by a glycolipid anchor.