In contrast to receptor tyrosine kinases (RTKS), non-receptor tyrosine kinases (NRTKs) do not have an extracellular and transmembrane domain. The majority of them are found within the cytoplasm of cells, including in immune cells. However, some NRTKS can also be anchored to the plasma membrane due to their differing N-terminus modifications. All of the nine families of NRTKs have Src homology (SH2) and 3 (SH3) domains.