Amino-Terminal Palmitate or Polybasic Domain Can Provide Required Second Signal to Myristate for Membrane Binding of P56 lck

Recent work has shown that several members of the src family of protein tyrosine kinases (PTKs) are modified by palmitoylation, including p56 lck and p59 fyn but not p60 src. Mapping of the sites of palmitoylation in p56 lck identified cys 3 as the major site and cys 5 as a minor site of palmitoylation. A non-palmitoylated p56 lck(cys 3,5→ser) mutant was localized exclusively in the cytoplasm despite the presence of amino-terminal myristoylation, thus indicating that palmitoylation of p56 lck was necessary for membrane binding. The addition of a domain of six lysine residues to a non-palmitoylated p56 lck mutant was sufficient to re-establish membrane binding but not to target the non-palmitoylated p56 lck to caveolae. These results establish that two signals, myristoylation plus either palmitoylation or a polybasic domain, are necessary for membrane binding of scr family PTKs.