TYRO3, also known as Axl (Ufo, Ark), Dtk (Sky, Tyro3, Rse, Brt) and Mer (human and mouse homologues of chicken c-Eyk) constitute a new receptor tyrosine kinase subfamily. TYRO3 protein is activated by the products of the growth arrest-specific gene 6 and protein S genes and is involved in controlling cell survival and proliferation, spermatogenesis, immunoregulation and phagocytosis. TYRO3 has also been identified as a cell entry factor for Ebola and Marburg viruses.