Characterisation of phosphoprotein complexes associated with rat thymocyte Thy-1.

We have previously demonstrated the non-covalent association of the protein tyrosine kinases p56lck and p60fyn together with a number of substrates for phosphorylation with rat thymocyte Thy-1. Here we present evidence that one of these associated phosphoproteins, p85, is associated by disulphide bridging with another polypeptide, demonstrating that it is an integral membrane protein with an extracellular domain. We also show that phosphatidylinositol 3 kinase activity may be coprecipitated with Thy-1 in Brij 96 thymocyte lysates.