Vascular endothelial growth factor receptor 1 (FLT1) is a protein that in humans is encoded by the FLT1 gene. Oncogene FLT belongs to the src gene family. It is mapped to 13q12. The deduced 1,338-amino acid protein has a calculated molecular mass of 150.6 kD. It has a 758-amino acid extracellular domain, followed by a 22-amino acid transmembrane region and a 558-amino acid cytoplasmic region containing a cluster of basic amino acids and a tyrosine kinase domain. sFLT-1 was identified in placenta, adult lung, kidney, liver and uterus. Like other members of this family, it shows tyrosine protein kinase activity that is important for the control of cell proliferation and differentiation.