MATERIALS AND METHODS Materials

tributing to a dual acylation motif. The Src family PTKs Yes, Fyn and Lck are both myristoylated and S-acylated whereas strate that the 10 amino acid N-terminal sequence of Lck is sufficient to confer localisation to the plasma membrane whenSrc itself, which does not contain a cysteine residue near the N terminus, is only myristoylated (Koegl et al., 1994; Shenoy-Scaria et al., 1993). S-acylation is dependent on prior co-trans-lational myristoylation of Lck and Fyn and is required for membrane attachment (Turner et al., 1990), reminiscent of the situation for Ras proteins (Hancock et al., 1989, 1990). The targeting of Src family PTKs to specific membrane compartments by attached lipid groups may play an important role during T cell activation by facilitating lipid-protein or protein-protein interactions. Glycosyl phosphatidylinositol (GPI)-anchored membrane proteins and the PTKs Lck and Fyn independently associate with a cold Triton X-100-insoluble fused to cytosolic proteins. The chimaeras also enter a Triton X-100-insoluble fraction which is promoted by S-acylation. The dual acylation motif can therefore be used as a general targeting signal to take proteins to these plasma membrane domains specialised for signalling (Lisanti et al., 1994)