sentences:  The SH3 domain of certain tyrosine kinases, such as the oncogene Src kinase, binds to cortactin's proline-rich region and phosphorylates it on Tyr421, Tyr466, and Tyr482.Once activated in this way, it can bind to filamentous actin (F-actin) with the fourth of its cortactin repeats.As the concentration of phosphorylated cortactin increases in specific regions within the cell, the monomers each begin to recruit an Arp2/3 complex to F-actin.