The SH3 domain of Mouse p130cas (CRK-associated substrate) or Bcar1 binds to a proline-rich sequence present in the C terminus of Mouse pp125FAK/ Focal adhesion kinase 1 (Fak1)/ Protein-tyrosine kinase 2 (Ptk2), a kinase which is activated upon cell adhesion, and this interaction is likely to be functionally important in integrin mediated signal transduction