Structure of signalling intermediates that exhibit aberrant expression in human breast cancer. (a) Schematic representation of the structures of c-Src and PLC-γ1 (class 1 SH2 domain-containing proteins) and Grb2 (a class II protein). PLC-γ1 has two regions (designated PLC in the figure) that constitute its catalytic domain, and the second pleckstrin homology (PH) domain is interrupted by SH2 and SH3 modules. The different proteins and their domains are not drawn to scale; for details refer to text. (b) Comparison of the molecular architectures of Grb7 and Caenorhabditis elegans mig10. These two proteins possess a homologous central region (termed the Grb-Mig or GM domain), which contains a PH domain. Other than the presence of proline-rich regions, however, the remainder of their structures are dissimilar. (c) Schematic representation of EMS1/cortactin. The filamentous actin-binding repeat region is separated from the carboxyl-terminal SH3 module by a predicted helical domain followed by a stretch of amino acids rich in serine, threonine and proline residues (together designated HP in the figure).