Members of the Src family of protein tyrosine kinases are thought to be involved in signal transduction pathways that control growth and cellular architecture. In recent years it has been shown that they interact with receptor tyrosine kinases (such as the platelet-derived growth factor receptor) and with receptors that themselves lack intrinsic tyrosine kinase activity (such as the interleukin-2 receptor). In some cases they are required for mitogenic signalling by these receptors. They are also activated in response to stress and during mitosis.